| Message ID | 20200821194310.3089815-14-keescook@chromium.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Warn on orphan section placement | expand |
Hi Kees, On Fri, Aug 21, 2020 at 9:56 PM Kees Cook <keescook@chromium.org> wrote: > In preparation for warning on orphan sections, discard > unwanted non-zero-sized generated sections, and enforce other > expected-to-be-zero-sized sections (since discarding them might hide > problems with them suddenly gaining unexpected entries). > > Suggested-by: Ard Biesheuvel <ardb@kernel.org> > Signed-off-by: Kees Cook <keescook@chromium.org> This is now commit be2881824ae9eb92 ("arm64/build: Assert for unwanted sections") in v5.10-rc1, and is causing the following error with renesas_defconfig[1]: aarch64-linux-gnu-ld: warning: orphan section `.eh_frame' from `kernel/bpf/core.o' being placed in section `.eh_frame' aarch64-linux-gnu-ld: Unexpected GOT/PLT entries detected! aarch64-linux-gnu-ld: Unexpected run-time procedure linkages detected! I cannot reproduce this with the standard arm64 defconfig. I bisected the error to the aforementioned commit, but understand this is not the real reason. If I revert this commit, I still get: aarch64-linux-gnu-ld: warning: orphan section `.got.plt' from `arch/arm64/kernel/head.o' being placed in section `.got.plt' aarch64-linux-gnu-ld: warning: orphan section `.plt' from `arch/arm64/kernel/head.o' being placed in section `.plt' aarch64-linux-gnu-ld: warning: orphan section `.data.rel.ro' from `arch/arm64/kernel/head.o' being placed in section `.data.rel.ro' aarch64-linux-gnu-ld: warning: orphan section `.eh_frame' from `kernel/bpf/core.o' being placed in section `.eh_frame' I.e. including the ".eh_frame" warning. I have tried bisecting that warning (i.e. with be2881824ae9eb92 reverted), but that leads me to commit b3e5d80d0c48c0cc ("arm64/build: Warn on orphan section placement"), which is another red herring. Note that even on plain be2881824ae9eb92, I get: aarch64-linux-gnu-ld: Unexpected GOT/PLT entries detected! aarch64-linux-gnu-ld: Unexpected run-time procedure linkages detected! The parent commit obviously doesn't show that (but probably still has the problem). Do you have a clue! Thanks! > --- a/arch/arm64/kernel/vmlinux.lds.S > +++ b/arch/arm64/kernel/vmlinux.lds.S > @@ -121,6 +121,14 @@ SECTIONS > *(.got) /* Global offset table */ > } > > + /* > + * Make sure that the .got.plt is either completely empty or it > + * contains only the lazy dispatch entries. > + */ > + .got.plt : { *(.got.plt) } > + ASSERT(SIZEOF(.got.plt) == 0 || SIZEOF(.got.plt) == 0x18, > + "Unexpected GOT/PLT entries detected!") > + > . = ALIGN(SEGMENT_ALIGN); > _etext = .; /* End of text section */ > > @@ -243,6 +251,18 @@ SECTIONS > ELF_DETAILS > > HEAD_SYMBOLS > + > + /* > + * Sections that should stay zero sized, which is safer to > + * explicitly check instead of blindly discarding. > + */ > + .plt : { > + *(.plt) *(.plt.*) *(.iplt) *(.igot) > + } > + ASSERT(SIZEOF(.plt) == 0, "Unexpected run-time procedure linkages detected!") > + > + .data.rel.ro : { *(.data.rel.ro) } > + ASSERT(SIZEOF(.data.rel.ro) == 0, "Unexpected RELRO detected!") > } > > #include "image-vars.h" [1] https://git.kernel.org/pub/scm/linux/kernel/git/geert/renesas-devel.git/log/?h=topic/renesas-defconfig Gr{oetje,eeting}s, Geert -- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like that. -- Linus Torvalds
Hi Kees, On Mon, Oct 26, 2020 at 1:29 PM Geert Uytterhoeven <geert@linux-m68k.org> wrote: > On Fri, Aug 21, 2020 at 9:56 PM Kees Cook <keescook@chromium.org> wrote: > > In preparation for warning on orphan sections, discard > > unwanted non-zero-sized generated sections, and enforce other > > expected-to-be-zero-sized sections (since discarding them might hide > > problems with them suddenly gaining unexpected entries). > > > > Suggested-by: Ard Biesheuvel <ardb@kernel.org> > > Signed-off-by: Kees Cook <keescook@chromium.org> > > This is now commit be2881824ae9eb92 ("arm64/build: Assert for unwanted > sections") in v5.10-rc1, and is causing the following error with > renesas_defconfig[1]: > > aarch64-linux-gnu-ld: warning: orphan section `.eh_frame' from > `kernel/bpf/core.o' being placed in section `.eh_frame' > aarch64-linux-gnu-ld: Unexpected GOT/PLT entries detected! > aarch64-linux-gnu-ld: Unexpected run-time procedure linkages detected! > > I cannot reproduce this with the standard arm64 defconfig. > > I bisected the error to the aforementioned commit, but understand this > is not the real reason. If I revert this commit, I still get: > > aarch64-linux-gnu-ld: warning: orphan section `.got.plt' from > `arch/arm64/kernel/head.o' being placed in section `.got.plt' > aarch64-linux-gnu-ld: warning: orphan section `.plt' from > `arch/arm64/kernel/head.o' being placed in section `.plt' > aarch64-linux-gnu-ld: warning: orphan section `.data.rel.ro' from > `arch/arm64/kernel/head.o' being placed in section `.data.rel.ro' > aarch64-linux-gnu-ld: warning: orphan section `.eh_frame' from > `kernel/bpf/core.o' being placed in section `.eh_frame' > > I.e. including the ".eh_frame" warning. I have tried bisecting that > warning (i.e. with be2881824ae9eb92 reverted), but that leads me to > commit b3e5d80d0c48c0cc ("arm64/build: Warn on orphan section > placement"), which is another red herring. kernel/bpf/core.o is the only file containing an eh_frame section, causing the warning. If I compile core.c with "-g" added, like arm64 defconfig does, the eh_frame section is no longer emitted. Hence setting CONFIG_DEBUG_INFO=y, cfr. arm64 defconfig, the warning is gone, but I'm back to the the "Unexpected GOT/PLT entries" below... > Note that even on plain be2881824ae9eb92, I get: > > aarch64-linux-gnu-ld: Unexpected GOT/PLT entries detected! > aarch64-linux-gnu-ld: Unexpected run-time procedure linkages detected! > > The parent commit obviously doesn't show that (but probably still has > the problem). Gr{oetje,eeting}s, Geert
On Mon, Oct 26, 2020 at 2:29 PM Geert Uytterhoeven <geert@linux-m68k.org> wrote: > On Mon, Oct 26, 2020 at 1:29 PM Geert Uytterhoeven <geert@linux-m68k.org> wrote: > > On Fri, Aug 21, 2020 at 9:56 PM Kees Cook <keescook@chromium.org> wrote: > > > In preparation for warning on orphan sections, discard > > > unwanted non-zero-sized generated sections, and enforce other > > > expected-to-be-zero-sized sections (since discarding them might hide > > > problems with them suddenly gaining unexpected entries). > > > > > > Suggested-by: Ard Biesheuvel <ardb@kernel.org> > > > Signed-off-by: Kees Cook <keescook@chromium.org> > > > > This is now commit be2881824ae9eb92 ("arm64/build: Assert for unwanted > > sections") in v5.10-rc1, and is causing the following error with > > renesas_defconfig[1]: > > > > aarch64-linux-gnu-ld: warning: orphan section `.eh_frame' from > > `kernel/bpf/core.o' being placed in section `.eh_frame' > > aarch64-linux-gnu-ld: Unexpected GOT/PLT entries detected! > > aarch64-linux-gnu-ld: Unexpected run-time procedure linkages detected! > > > > I cannot reproduce this with the standard arm64 defconfig. > > > > I bisected the error to the aforementioned commit, but understand this > > is not the real reason. If I revert this commit, I still get: > > > > aarch64-linux-gnu-ld: warning: orphan section `.got.plt' from > > `arch/arm64/kernel/head.o' being placed in section `.got.plt' > > aarch64-linux-gnu-ld: warning: orphan section `.plt' from > > `arch/arm64/kernel/head.o' being placed in section `.plt' > > aarch64-linux-gnu-ld: warning: orphan section `.data.rel.ro' from > > `arch/arm64/kernel/head.o' being placed in section `.data.rel.ro' > > aarch64-linux-gnu-ld: warning: orphan section `.eh_frame' from > > `kernel/bpf/core.o' being placed in section `.eh_frame' > > > > I.e. including the ".eh_frame" warning. I have tried bisecting that > > warning (i.e. with be2881824ae9eb92 reverted), but that leads me to > > commit b3e5d80d0c48c0cc ("arm64/build: Warn on orphan section > > placement"), which is another red herring. > > kernel/bpf/core.o is the only file containing an eh_frame section, > causing the warning. > If I compile core.c with "-g" added, like arm64 defconfig does, the > eh_frame section is no longer emitted. > > Hence setting CONFIG_DEBUG_INFO=y, cfr. arm64 defconfig, the warning > is gone, but I'm back to the the "Unexpected GOT/PLT entries" below... > > > Note that even on plain be2881824ae9eb92, I get: > > > > aarch64-linux-gnu-ld: Unexpected GOT/PLT entries detected! > > aarch64-linux-gnu-ld: Unexpected run-time procedure linkages detected! > > > > The parent commit obviously doesn't show that (but probably still has > > the problem). Reverting both b3e5d80d0c48c0cc ("arm64/build: Warn on orphan section placement") be2881824ae9eb92 ("arm64/build: Assert for unwanted sections") seems to solve my problems, without any ill effects? Gr{oetje,eeting}s, Geert
On Mon, 26 Oct 2020 at 17:01, Geert Uytterhoeven <geert@linux-m68k.org> wrote: > > On Mon, Oct 26, 2020 at 2:29 PM Geert Uytterhoeven <geert@linux-m68k.org> wrote: > > On Mon, Oct 26, 2020 at 1:29 PM Geert Uytterhoeven <geert@linux-m68k.org> wrote: > > > On Fri, Aug 21, 2020 at 9:56 PM Kees Cook <keescook@chromium.org> wrote: > > > > In preparation for warning on orphan sections, discard > > > > unwanted non-zero-sized generated sections, and enforce other > > > > expected-to-be-zero-sized sections (since discarding them might hide > > > > problems with them suddenly gaining unexpected entries). > > > > > > > > Suggested-by: Ard Biesheuvel <ardb@kernel.org> > > > > Signed-off-by: Kees Cook <keescook@chromium.org> > > > > > > This is now commit be2881824ae9eb92 ("arm64/build: Assert for unwanted > > > sections") in v5.10-rc1, and is causing the following error with > > > renesas_defconfig[1]: > > > > > > aarch64-linux-gnu-ld: warning: orphan section `.eh_frame' from > > > `kernel/bpf/core.o' being placed in section `.eh_frame' > > > aarch64-linux-gnu-ld: Unexpected GOT/PLT entries detected! > > > aarch64-linux-gnu-ld: Unexpected run-time procedure linkages detected! > > > > > > I cannot reproduce this with the standard arm64 defconfig. > > > > > > I bisected the error to the aforementioned commit, but understand this > > > is not the real reason. If I revert this commit, I still get: > > > > > > aarch64-linux-gnu-ld: warning: orphan section `.got.plt' from > > > `arch/arm64/kernel/head.o' being placed in section `.got.plt' > > > aarch64-linux-gnu-ld: warning: orphan section `.plt' from > > > `arch/arm64/kernel/head.o' being placed in section `.plt' > > > aarch64-linux-gnu-ld: warning: orphan section `.data.rel.ro' from > > > `arch/arm64/kernel/head.o' being placed in section `.data.rel.ro' > > > aarch64-linux-gnu-ld: warning: orphan section `.eh_frame' from > > > `kernel/bpf/core.o' being placed in section `.eh_frame' > > > > > > I.e. including the ".eh_frame" warning. I have tried bisecting that > > > warning (i.e. with be2881824ae9eb92 reverted), but that leads me to > > > commit b3e5d80d0c48c0cc ("arm64/build: Warn on orphan section > > > placement"), which is another red herring. > > > > kernel/bpf/core.o is the only file containing an eh_frame section, > > causing the warning. > > If I compile core.c with "-g" added, like arm64 defconfig does, the > > eh_frame section is no longer emitted. > > > > Hence setting CONFIG_DEBUG_INFO=y, cfr. arm64 defconfig, the warning > > is gone, but I'm back to the the "Unexpected GOT/PLT entries" below... > > > > > Note that even on plain be2881824ae9eb92, I get: > > > > > > aarch64-linux-gnu-ld: Unexpected GOT/PLT entries detected! > > > aarch64-linux-gnu-ld: Unexpected run-time procedure linkages detected! > > > > > > The parent commit obviously doesn't show that (but probably still has > > > the problem). > > Reverting both > b3e5d80d0c48c0cc ("arm64/build: Warn on orphan section placement") > be2881824ae9eb92 ("arm64/build: Assert for unwanted sections") > seems to solve my problems, without any ill effects? > I cannot reproduce the issue here with my distro GCC+binutils (Debian 8.3.0) The presence of .data.rel.ro and .got.plt sections suggests that the toolchain is using -fpie and/or -z relro to build shared objects rather than a fully linked bare metal binary. Which toolchain are you using? Does adding -fno-pie to the compiler command line and/or adding -z norelro to the linker command line make any difference?
Hi Ard, On Mon, Oct 26, 2020 at 6:39 PM Ard Biesheuvel <ardb@kernel.org> wrote: > On Mon, 26 Oct 2020 at 17:01, Geert Uytterhoeven <geert@linux-m68k.org> wrote: > > On Mon, Oct 26, 2020 at 2:29 PM Geert Uytterhoeven <geert@linux-m68k.org> wrote: > > > On Mon, Oct 26, 2020 at 1:29 PM Geert Uytterhoeven <geert@linux-m68k.org> wrote: > > > > On Fri, Aug 21, 2020 at 9:56 PM Kees Cook <keescook@chromium.org> wrote: > > > > > In preparation for warning on orphan sections, discard > > > > > unwanted non-zero-sized generated sections, and enforce other > > > > > expected-to-be-zero-sized sections (since discarding them might hide > > > > > problems with them suddenly gaining unexpected entries). > > > > > > > > > > Suggested-by: Ard Biesheuvel <ardb@kernel.org> > > > > > Signed-off-by: Kees Cook <keescook@chromium.org> > > > > > > > > This is now commit be2881824ae9eb92 ("arm64/build: Assert for unwanted > > > > sections") in v5.10-rc1, and is causing the following error with > > > > renesas_defconfig[1]: > > > > > > > > aarch64-linux-gnu-ld: warning: orphan section `.eh_frame' from > > > > `kernel/bpf/core.o' being placed in section `.eh_frame' > > > > aarch64-linux-gnu-ld: Unexpected GOT/PLT entries detected! > > > > aarch64-linux-gnu-ld: Unexpected run-time procedure linkages detected! > > > > > > > > I cannot reproduce this with the standard arm64 defconfig. > > > > > > > > I bisected the error to the aforementioned commit, but understand this > > > > is not the real reason. If I revert this commit, I still get: > > > > > > > > aarch64-linux-gnu-ld: warning: orphan section `.got.plt' from > > > > `arch/arm64/kernel/head.o' being placed in section `.got.plt' > > > > aarch64-linux-gnu-ld: warning: orphan section `.plt' from > > > > `arch/arm64/kernel/head.o' being placed in section `.plt' > > > > aarch64-linux-gnu-ld: warning: orphan section `.data.rel.ro' from > > > > `arch/arm64/kernel/head.o' being placed in section `.data.rel.ro' > > > > aarch64-linux-gnu-ld: warning: orphan section `.eh_frame' from > > > > `kernel/bpf/core.o' being placed in section `.eh_frame' > > > > > > > > I.e. including the ".eh_frame" warning. I have tried bisecting that > > > > warning (i.e. with be2881824ae9eb92 reverted), but that leads me to > > > > commit b3e5d80d0c48c0cc ("arm64/build: Warn on orphan section > > > > placement"), which is another red herring. > > > > > > kernel/bpf/core.o is the only file containing an eh_frame section, > > > causing the warning. > > > If I compile core.c with "-g" added, like arm64 defconfig does, the > > > eh_frame section is no longer emitted. > > > > > > Hence setting CONFIG_DEBUG_INFO=y, cfr. arm64 defconfig, the warning > > > is gone, but I'm back to the the "Unexpected GOT/PLT entries" below... > > > > > > > Note that even on plain be2881824ae9eb92, I get: > > > > > > > > aarch64-linux-gnu-ld: Unexpected GOT/PLT entries detected! > > > > aarch64-linux-gnu-ld: Unexpected run-time procedure linkages detected! > > > > > > > > The parent commit obviously doesn't show that (but probably still has > > > > the problem). > > > > Reverting both > > b3e5d80d0c48c0cc ("arm64/build: Warn on orphan section placement") > > be2881824ae9eb92 ("arm64/build: Assert for unwanted sections") > > seems to solve my problems, without any ill effects? > > > > I cannot reproduce the issue here with my distro GCC+binutils (Debian 8.3.0) > > The presence of .data.rel.ro and .got.plt sections suggests that the > toolchain is using -fpie and/or -z relro to build shared objects > rather than a fully linked bare metal binary. > > Which toolchain are you using? Does adding -fno-pie to the compiler gcc version 9.3.0 (Ubuntu 9.3.0-17ubuntu1~20.04) from Ubuntu 20.04LTS. > command line and/or adding -z norelro to the linker command line make > any difference? I'll give that a try later... Gr{oetje,eeting}s, Geert
On Mon, Oct 26, 2020 at 10:44 AM Geert Uytterhoeven <geert@linux-m68k.org> wrote: > > Hi Ard, > > On Mon, Oct 26, 2020 at 6:39 PM Ard Biesheuvel <ardb@kernel.org> wrote: > > On Mon, 26 Oct 2020 at 17:01, Geert Uytterhoeven <geert@linux-m68k.org> wrote: > > > On Mon, Oct 26, 2020 at 2:29 PM Geert Uytterhoeven <geert@linux-m68k.org> wrote: > > > > On Mon, Oct 26, 2020 at 1:29 PM Geert Uytterhoeven <geert@linux-m68k.org> wrote: > > > > > On Fri, Aug 21, 2020 at 9:56 PM Kees Cook <keescook@chromium.org> wrote: > > > > > > In preparation for warning on orphan sections, discard > > > > > > unwanted non-zero-sized generated sections, and enforce other > > > > > > expected-to-be-zero-sized sections (since discarding them might hide > > > > > > problems with them suddenly gaining unexpected entries). > > > > > > > > > > > > Suggested-by: Ard Biesheuvel <ardb@kernel.org> > > > > > > Signed-off-by: Kees Cook <keescook@chromium.org> > > > > > > > > > > This is now commit be2881824ae9eb92 ("arm64/build: Assert for unwanted > > > > > sections") in v5.10-rc1, and is causing the following error with > > > > > renesas_defconfig[1]: > > > > > > > > > > aarch64-linux-gnu-ld: warning: orphan section `.eh_frame' from > > > > > `kernel/bpf/core.o' being placed in section `.eh_frame' > > > > > aarch64-linux-gnu-ld: Unexpected GOT/PLT entries detected! > > > > > aarch64-linux-gnu-ld: Unexpected run-time procedure linkages detected! > > > > > > > > > > I cannot reproduce this with the standard arm64 defconfig. > > > > > > > > > > I bisected the error to the aforementioned commit, but understand this > > > > > is not the real reason. If I revert this commit, I still get: > > > > > > > > > > aarch64-linux-gnu-ld: warning: orphan section `.got.plt' from > > > > > `arch/arm64/kernel/head.o' being placed in section `.got.plt' > > > > > aarch64-linux-gnu-ld: warning: orphan section `.plt' from > > > > > `arch/arm64/kernel/head.o' being placed in section `.plt' > > > > > aarch64-linux-gnu-ld: warning: orphan section `.data.rel.ro' from > > > > > `arch/arm64/kernel/head.o' being placed in section `.data.rel.ro' > > > > > aarch64-linux-gnu-ld: warning: orphan section `.eh_frame' from > > > > > `kernel/bpf/core.o' being placed in section `.eh_frame' > > > > > > > > > > I.e. including the ".eh_frame" warning. I have tried bisecting that > > > > > warning (i.e. with be2881824ae9eb92 reverted), but that leads me to > > > > > commit b3e5d80d0c48c0cc ("arm64/build: Warn on orphan section > > > > > placement"), which is another red herring. > > > > > > > > kernel/bpf/core.o is the only file containing an eh_frame section, > > > > causing the warning. When I see .eh_frame, I think -fno-asynchronous-unwind-tables is missing from someone's KBUILD_CFLAGS. But I don't see anything curious in kernel/bpf/Makefile, unless cc-disable-warning is somehow broken. > > > > If I compile core.c with "-g" added, like arm64 defconfig does, the > > > > eh_frame section is no longer emitted. > > > > > > > > Hence setting CONFIG_DEBUG_INFO=y, cfr. arm64 defconfig, the warning > > > > is gone, but I'm back to the the "Unexpected GOT/PLT entries" below... > > > > > > > > > Note that even on plain be2881824ae9eb92, I get: > > > > > > > > > > aarch64-linux-gnu-ld: Unexpected GOT/PLT entries detected! > > > > > aarch64-linux-gnu-ld: Unexpected run-time procedure linkages detected! > > > > > > > > > > The parent commit obviously doesn't show that (but probably still has > > > > > the problem). > > > > > > Reverting both > > > b3e5d80d0c48c0cc ("arm64/build: Warn on orphan section placement") > > > be2881824ae9eb92 ("arm64/build: Assert for unwanted sections") > > > seems to solve my problems, without any ill effects? > > > > > > > I cannot reproduce the issue here with my distro GCC+binutils (Debian 8.3.0) > > > > The presence of .data.rel.ro and .got.plt sections suggests that the > > toolchain is using -fpie and/or -z relro to build shared objects > > rather than a fully linked bare metal binary. > > > > Which toolchain are you using? Does adding -fno-pie to the compiler > > gcc version 9.3.0 (Ubuntu 9.3.0-17ubuntu1~20.04) from Ubuntu 20.04LTS. > > > command line and/or adding -z norelro to the linker command line make > > any difference? > > I'll give that a try later... This patch just got picked up into the for-next branch of the arm64 tree; it enables `-z norelro` regardless of configs. https://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git/commit/?h=for-next/core&id=3b92fa7485eba16b05166fddf38ab42f2ff6ab95 If you apply that, that should help you test `-z norelro` quickly.
Hi Nick, On Mon, Oct 26, 2020 at 6:49 PM Nick Desaulniers <ndesaulniers@google.com> wrote: > On Mon, Oct 26, 2020 at 10:44 AM Geert Uytterhoeven > <geert@linux-m68k.org> wrote: > > On Mon, Oct 26, 2020 at 6:39 PM Ard Biesheuvel <ardb@kernel.org> wrote: > > > On Mon, 26 Oct 2020 at 17:01, Geert Uytterhoeven <geert@linux-m68k.org> wrote: > > > > On Mon, Oct 26, 2020 at 2:29 PM Geert Uytterhoeven <geert@linux-m68k.org> wrote: > > > > > On Mon, Oct 26, 2020 at 1:29 PM Geert Uytterhoeven <geert@linux-m68k.org> wrote: > > > > > > On Fri, Aug 21, 2020 at 9:56 PM Kees Cook <keescook@chromium.org> wrote: > > > > > > > In preparation for warning on orphan sections, discard > > > > > > > unwanted non-zero-sized generated sections, and enforce other > > > > > > > expected-to-be-zero-sized sections (since discarding them might hide > > > > > > > problems with them suddenly gaining unexpected entries). > > > > > > > > > > > > > > Suggested-by: Ard Biesheuvel <ardb@kernel.org> > > > > > > > Signed-off-by: Kees Cook <keescook@chromium.org> > > > > > > > > > > > > This is now commit be2881824ae9eb92 ("arm64/build: Assert for unwanted > > > > > > sections") in v5.10-rc1, and is causing the following error with > > > > > > renesas_defconfig[1]: > > > > > > > > > > > > aarch64-linux-gnu-ld: warning: orphan section `.eh_frame' from > > > > > > `kernel/bpf/core.o' being placed in section `.eh_frame' > > > > > > aarch64-linux-gnu-ld: Unexpected GOT/PLT entries detected! > > > > > > aarch64-linux-gnu-ld: Unexpected run-time procedure linkages detected! > > > > > > > > > > > > I cannot reproduce this with the standard arm64 defconfig. > > > > > > > > > > > > I bisected the error to the aforementioned commit, but understand this > > > > > > is not the real reason. If I revert this commit, I still get: > > > > > > > > > > > > aarch64-linux-gnu-ld: warning: orphan section `.got.plt' from > > > > > > `arch/arm64/kernel/head.o' being placed in section `.got.plt' > > > > > > aarch64-linux-gnu-ld: warning: orphan section `.plt' from > > > > > > `arch/arm64/kernel/head.o' being placed in section `.plt' > > > > > > aarch64-linux-gnu-ld: warning: orphan section `.data.rel.ro' from > > > > > > `arch/arm64/kernel/head.o' being placed in section `.data.rel.ro' > > > > > > aarch64-linux-gnu-ld: warning: orphan section `.eh_frame' from > > > > > > `kernel/bpf/core.o' being placed in section `.eh_frame' > > > > > > > > > > > > I.e. including the ".eh_frame" warning. I have tried bisecting that > > > > > > warning (i.e. with be2881824ae9eb92 reverted), but that leads me to > > > > > > commit b3e5d80d0c48c0cc ("arm64/build: Warn on orphan section > > > > > > placement"), which is another red herring. > > > > > > > > > > kernel/bpf/core.o is the only file containing an eh_frame section, > > > > > causing the warning. > > When I see .eh_frame, I think -fno-asynchronous-unwind-tables is > missing from someone's KBUILD_CFLAGS. > But I don't see anything curious in kernel/bpf/Makefile, unless > cc-disable-warning is somehow broken. Yeah, I noticed it's added in arch/arm64/Makefile, and verified that it is actually passed when building kernel/bpf/core.o. > > > > > If I compile core.c with "-g" added, like arm64 defconfig does, the > > > > > eh_frame section is no longer emitted. > > > > > > > > > > Hence setting CONFIG_DEBUG_INFO=y, cfr. arm64 defconfig, the warning > > > > > is gone, but I'm back to the the "Unexpected GOT/PLT entries" below... > > > > > > > > > > > Note that even on plain be2881824ae9eb92, I get: > > > > > > > > > > > > aarch64-linux-gnu-ld: Unexpected GOT/PLT entries detected! > > > > > > aarch64-linux-gnu-ld: Unexpected run-time procedure linkages detected! > > > > > > > > > > > > The parent commit obviously doesn't show that (but probably still has > > > > > > the problem). > > > > > > > > Reverting both > > > > b3e5d80d0c48c0cc ("arm64/build: Warn on orphan section placement") > > > > be2881824ae9eb92 ("arm64/build: Assert for unwanted sections") > > > > seems to solve my problems, without any ill effects? > > > > > > > > > > I cannot reproduce the issue here with my distro GCC+binutils (Debian 8.3.0) > > > > > > The presence of .data.rel.ro and .got.plt sections suggests that the > > > toolchain is using -fpie and/or -z relro to build shared objects > > > rather than a fully linked bare metal binary. > > > > > > Which toolchain are you using? Does adding -fno-pie to the compiler > > > > gcc version 9.3.0 (Ubuntu 9.3.0-17ubuntu1~20.04) from Ubuntu 20.04LTS. > > > > > command line and/or adding -z norelro to the linker command line make > > > any difference? > > > > I'll give that a try later... > > This patch just got picked up into the for-next branch of the arm64 > tree; it enables `-z norelro` regardless of configs. > https://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git/commit/?h=for-next/core&id=3b92fa7485eba16b05166fddf38ab42f2ff6ab95 > If you apply that, that should help you test `-z norelro` quickly. Thanks, will give that a try, too. Gr{oetje,eeting}s, Geert
Hi Nick, On Mon, Oct 26, 2020 at 6:53 PM Geert Uytterhoeven <geert@linux-m68k.org> wrote: > On Mon, Oct 26, 2020 at 6:49 PM Nick Desaulniers > <ndesaulniers@google.com> wrote: > > On Mon, Oct 26, 2020 at 10:44 AM Geert Uytterhoeven > > <geert@linux-m68k.org> wrote: > > > On Mon, Oct 26, 2020 at 6:39 PM Ard Biesheuvel <ardb@kernel.org> wrote: > > > > On Mon, 26 Oct 2020 at 17:01, Geert Uytterhoeven <geert@linux-m68k.org> wrote: > > > > > On Mon, Oct 26, 2020 at 2:29 PM Geert Uytterhoeven <geert@linux-m68k.org> wrote: > > > > > > On Mon, Oct 26, 2020 at 1:29 PM Geert Uytterhoeven <geert@linux-m68k.org> wrote: > > > > > > > On Fri, Aug 21, 2020 at 9:56 PM Kees Cook <keescook@chromium.org> wrote: > > > > > > > > In preparation for warning on orphan sections, discard > > > > > > > > unwanted non-zero-sized generated sections, and enforce other > > > > > > > > expected-to-be-zero-sized sections (since discarding them might hide > > > > > > > > problems with them suddenly gaining unexpected entries). > > > > > > > > > > > > > > > > Suggested-by: Ard Biesheuvel <ardb@kernel.org> > > > > > > > > Signed-off-by: Kees Cook <keescook@chromium.org> > > > > > > > > > > > > > > This is now commit be2881824ae9eb92 ("arm64/build: Assert for unwanted > > > > > > > sections") in v5.10-rc1, and is causing the following error with > > > > > > > renesas_defconfig[1]: > > > > > > > > > > > > > > aarch64-linux-gnu-ld: warning: orphan section `.eh_frame' from > > > > > > > `kernel/bpf/core.o' being placed in section `.eh_frame' > > > > > > > aarch64-linux-gnu-ld: Unexpected GOT/PLT entries detected! > > > > > > > aarch64-linux-gnu-ld: Unexpected run-time procedure linkages detected! > > > > > > > > > > > > > > I cannot reproduce this with the standard arm64 defconfig. > > > > > > > > > > > > > > I bisected the error to the aforementioned commit, but understand this > > > > > > > is not the real reason. If I revert this commit, I still get: > > > > > > > > > > > > > > aarch64-linux-gnu-ld: warning: orphan section `.got.plt' from > > > > > > > `arch/arm64/kernel/head.o' being placed in section `.got.plt' > > > > > > > aarch64-linux-gnu-ld: warning: orphan section `.plt' from > > > > > > > `arch/arm64/kernel/head.o' being placed in section `.plt' > > > > > > > aarch64-linux-gnu-ld: warning: orphan section `.data.rel.ro' from > > > > > > > `arch/arm64/kernel/head.o' being placed in section `.data.rel.ro' > > > > > > > aarch64-linux-gnu-ld: warning: orphan section `.eh_frame' from > > > > > > > `kernel/bpf/core.o' being placed in section `.eh_frame' > > > > > > > > > > > > > > I.e. including the ".eh_frame" warning. I have tried bisecting that > > > > > > > warning (i.e. with be2881824ae9eb92 reverted), but that leads me to > > > > > > > commit b3e5d80d0c48c0cc ("arm64/build: Warn on orphan section > > > > > > > placement"), which is another red herring. > > > > > > > > > > > > kernel/bpf/core.o is the only file containing an eh_frame section, > > > > > > causing the warning. > > > > When I see .eh_frame, I think -fno-asynchronous-unwind-tables is > > missing from someone's KBUILD_CFLAGS. > > But I don't see anything curious in kernel/bpf/Makefile, unless > > cc-disable-warning is somehow broken. > > Yeah, I noticed it's added in arch/arm64/Makefile, and verified that it is > actually passed when building kernel/bpf/core.o. > > > > > > > If I compile core.c with "-g" added, like arm64 defconfig does, the > > > > > > eh_frame section is no longer emitted. > > > > > > > > > > > > Hence setting CONFIG_DEBUG_INFO=y, cfr. arm64 defconfig, the warning > > > > > > is gone, but I'm back to the the "Unexpected GOT/PLT entries" below... > > > > > > > > > > > > > Note that even on plain be2881824ae9eb92, I get: > > > > > > > > > > > > > > aarch64-linux-gnu-ld: Unexpected GOT/PLT entries detected! > > > > > > > aarch64-linux-gnu-ld: Unexpected run-time procedure linkages detected! > > > > > > > > > > > > > > The parent commit obviously doesn't show that (but probably still has > > > > > > > the problem). > > > > > > > > > > Reverting both > > > > > b3e5d80d0c48c0cc ("arm64/build: Warn on orphan section placement") > > > > > be2881824ae9eb92 ("arm64/build: Assert for unwanted sections") > > > > > seems to solve my problems, without any ill effects? > > > > > > > > > > > > > I cannot reproduce the issue here with my distro GCC+binutils (Debian 8.3.0) > > > > > > > > The presence of .data.rel.ro and .got.plt sections suggests that the > > > > toolchain is using -fpie and/or -z relro to build shared objects > > > > rather than a fully linked bare metal binary. > > > > > > > > Which toolchain are you using? Does adding -fno-pie to the compiler > > > > > > gcc version 9.3.0 (Ubuntu 9.3.0-17ubuntu1~20.04) from Ubuntu 20.04LTS. > > > > > > > command line and/or adding -z norelro to the linker command line make > > > > any difference? > > > > > > I'll give that a try later... > > > > This patch just got picked up into the for-next branch of the arm64 > > tree; it enables `-z norelro` regardless of configs. > > https://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git/commit/?h=for-next/core&id=3b92fa7485eba16b05166fddf38ab42f2ff6ab95 > > If you apply that, that should help you test `-z norelro` quickly. > > Thanks, will give that a try, too. Commit 3b92fa7485eba16b05166fddf38ab42f2ff6ab95 is part of v5.10-rc1, so it was already included, and thus doesn't fix the issue. Gr{oetje,eeting}s, Geert
Hi Ard, On Mon, Oct 26, 2020 at 6:43 PM Geert Uytterhoeven <geert@linux-m68k.org> wrote: > On Mon, Oct 26, 2020 at 6:39 PM Ard Biesheuvel <ardb@kernel.org> wrote: > > On Mon, 26 Oct 2020 at 17:01, Geert Uytterhoeven <geert@linux-m68k.org> wrote: > > > On Mon, Oct 26, 2020 at 2:29 PM Geert Uytterhoeven <geert@linux-m68k.org> wrote: > > > > On Mon, Oct 26, 2020 at 1:29 PM Geert Uytterhoeven <geert@linux-m68k.org> wrote: > > > > > On Fri, Aug 21, 2020 at 9:56 PM Kees Cook <keescook@chromium.org> wrote: > > > > > > In preparation for warning on orphan sections, discard > > > > > > unwanted non-zero-sized generated sections, and enforce other > > > > > > expected-to-be-zero-sized sections (since discarding them might hide > > > > > > problems with them suddenly gaining unexpected entries). > > > > > > > > > > > > Suggested-by: Ard Biesheuvel <ardb@kernel.org> > > > > > > Signed-off-by: Kees Cook <keescook@chromium.org> > > > > > > > > > > This is now commit be2881824ae9eb92 ("arm64/build: Assert for unwanted > > > > > sections") in v5.10-rc1, and is causing the following error with > > > > > renesas_defconfig[1]: > > > > > > > > > > aarch64-linux-gnu-ld: warning: orphan section `.eh_frame' from > > > > > `kernel/bpf/core.o' being placed in section `.eh_frame' > > > > > aarch64-linux-gnu-ld: Unexpected GOT/PLT entries detected! > > > > > aarch64-linux-gnu-ld: Unexpected run-time procedure linkages detected! > > > > > > > > > > I cannot reproduce this with the standard arm64 defconfig. > > > > > > > > > > I bisected the error to the aforementioned commit, but understand this > > > > > is not the real reason. If I revert this commit, I still get: > > > > > > > > > > aarch64-linux-gnu-ld: warning: orphan section `.got.plt' from > > > > > `arch/arm64/kernel/head.o' being placed in section `.got.plt' > > > > > aarch64-linux-gnu-ld: warning: orphan section `.plt' from > > > > > `arch/arm64/kernel/head.o' being placed in section `.plt' > > > > > aarch64-linux-gnu-ld: warning: orphan section `.data.rel.ro' from > > > > > `arch/arm64/kernel/head.o' being placed in section `.data.rel.ro' > > > > > aarch64-linux-gnu-ld: warning: orphan section `.eh_frame' from > > > > > `kernel/bpf/core.o' being placed in section `.eh_frame' > > > > > > > > > > I.e. including the ".eh_frame" warning. I have tried bisecting that > > > > > warning (i.e. with be2881824ae9eb92 reverted), but that leads me to > > > > > commit b3e5d80d0c48c0cc ("arm64/build: Warn on orphan section > > > > > placement"), which is another red herring. > > > > > > > > kernel/bpf/core.o is the only file containing an eh_frame section, > > > > causing the warning. > > > > If I compile core.c with "-g" added, like arm64 defconfig does, the > > > > eh_frame section is no longer emitted. > > > > > > > > Hence setting CONFIG_DEBUG_INFO=y, cfr. arm64 defconfig, the warning > > > > is gone, but I'm back to the the "Unexpected GOT/PLT entries" below... > > > > > > > > > Note that even on plain be2881824ae9eb92, I get: > > > > > > > > > > aarch64-linux-gnu-ld: Unexpected GOT/PLT entries detected! > > > > > aarch64-linux-gnu-ld: Unexpected run-time procedure linkages detected! > > > > > > > > > > The parent commit obviously doesn't show that (but probably still has > > > > > the problem). > > > > > > Reverting both > > > b3e5d80d0c48c0cc ("arm64/build: Warn on orphan section placement") > > > be2881824ae9eb92 ("arm64/build: Assert for unwanted sections") > > > seems to solve my problems, without any ill effects? > > > > > > > I cannot reproduce the issue here with my distro GCC+binutils (Debian 8.3.0) > > > > The presence of .data.rel.ro and .got.plt sections suggests that the > > toolchain is using -fpie and/or -z relro to build shared objects > > rather than a fully linked bare metal binary. > > > > Which toolchain are you using? Does adding -fno-pie to the compiler > > gcc version 9.3.0 (Ubuntu 9.3.0-17ubuntu1~20.04) from Ubuntu 20.04LTS. > > > command line and/or adding -z norelro to the linker command line make > > any difference? > > I'll give that a try later... Adding -fno-pie to KBUILD_AFLAGS and KBUILD_CFLAGS doesn't make a difference. Same for adding -z norelno to the final link command: aarch64-linux-gnu-ld: warning: -z norelno ignored aarch64-linux-gnu-ld: warning: orphan section `.eh_frame' from `kernel/bpf/core.o' being placed in section `.eh_frame' aarch64-linux-gnu-ld: Unexpected GOT/PLT entries detected! aarch64-linux-gnu-ld: Unexpected run-time procedure linkages detected! Gr{oetje,eeting}s, Geert
Hi, On Mon, Oct 26, 2020 at 06:38:46PM +0100, Ard Biesheuvel wrote: > > > > Note that even on plain be2881824ae9eb92, I get: > > > > > > > > aarch64-linux-gnu-ld: Unexpected GOT/PLT entries detected! > > > > aarch64-linux-gnu-ld: Unexpected run-time procedure linkages detected! > > > > > > > > The parent commit obviously doesn't show that (but probably still has > > > > the problem). > > > > Reverting both > > b3e5d80d0c48c0cc ("arm64/build: Warn on orphan section placement") > > be2881824ae9eb92 ("arm64/build: Assert for unwanted sections") > > seems to solve my problems, without any ill effects? > > > > I cannot reproduce the issue here with my distro GCC+binutils (Debian 8.3.0) I have the same problem with one of my debug configs and Linux v5.10-rc1, and can reproduce with the Debian 8.3.0 toolchain, by using the arm64 defconfig and disabling CONFIG_MODULES: ld -EL -maarch64elf --no-undefined -X -z norelro -shared -Bsymbolic -z notext --no-apply-dynamic-relocs --fix-cortex-a53-843419 --orphan-handling=warn --build-id=sha1 --strip-debug -o .tmp_vmlinux.kallsyms1 -T ./arch/arm64/kernel/vmlinux.lds --whole-archive arch/arm64/kernel/head.o init/built-in.a usr/built-in.a arch/arm64/built-in.a kernel/built-in.a certs/built-in.a mm/built-in.a fs/built-in.a ipc/built-in.a security/built-in.a crypto/built-in.a block/built-in.a arch/arm64/lib/built-in.a lib/built-in.a drivers/built-in.a sound/built-in.a net/built-in.a virt/built-in.a --no-whole-archive --start-group arch/arm64/lib/lib.a lib/lib.a ./drivers/firmware/efi/libstub/lib.a --end-group ld: Unexpected GOT/PLT entries detected! ld: Unexpected run-time procedure linkages detected! Adding -fno-pie to this command doesn't fix the problem. Note that when cross-building with a GCC 10.2 and binutils 2.35.1 I also get several "aarch64-linux-gnu-ld: warning: -z norelro ignored" in addition to the error, but I don't get that warning with the 8.3.0 toolchain. Thanks, Jean > > The presence of .data.rel.ro and .got.plt sections suggests that the > toolchain is using -fpie and/or -z relro to build shared objects > rather than a fully linked bare metal binary. > > Which toolchain are you using? Does adding -fno-pie to the compiler > command line and/or adding -z norelro to the linker command line make > any difference? > > _______________________________________________ > linux-arm-kernel mailing list > linux-arm-kernel@lists.infradead.org > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
Hi Jean-Philippe, On Tue, Oct 27, 2020 at 11:09 AM Jean-Philippe Brucker <jean-philippe@linaro.org> wrote: > On Mon, Oct 26, 2020 at 06:38:46PM +0100, Ard Biesheuvel wrote: > > > > > Note that even on plain be2881824ae9eb92, I get: > > > > > > > > > > aarch64-linux-gnu-ld: Unexpected GOT/PLT entries detected! > > > > > aarch64-linux-gnu-ld: Unexpected run-time procedure linkages detected! > > > > > > > > > > The parent commit obviously doesn't show that (but probably still has > > > > > the problem). > > > > > > Reverting both > > > b3e5d80d0c48c0cc ("arm64/build: Warn on orphan section placement") > > > be2881824ae9eb92 ("arm64/build: Assert for unwanted sections") > > > seems to solve my problems, without any ill effects? > > > > > > > I cannot reproduce the issue here with my distro GCC+binutils (Debian 8.3.0) > > I have the same problem with one of my debug configs and Linux v5.10-rc1, > and can reproduce with the Debian 8.3.0 toolchain, by using the arm64 > defconfig and disabling CONFIG_MODULES: > > ld -EL -maarch64elf --no-undefined -X -z norelro -shared -Bsymbolic -z notext --no-apply-dynamic-relocs --fix-cortex-a53-843419 --orphan-handling=warn --build-id=sha1 --strip-debug -o .tmp_vmlinux.kallsyms1 -T ./arch/arm64/kernel/vmlinux.lds --whole-archive arch/arm64/kernel/head.o init/built-in.a usr/built-in.a arch/arm64/built-in.a kernel/built-in.a certs/built-in.a mm/built-in.a fs/built-in.a ipc/built-in.a security/built-in.a crypto/built-in.a block/built-in.a arch/arm64/lib/built-in.a lib/built-in.a drivers/built-in.a sound/built-in.a net/built-in.a virt/built-in.a --no-whole-archive --start-group arch/arm64/lib/lib.a lib/lib.a ./drivers/firmware/efi/libstub/lib.a --end-group > ld: Unexpected GOT/PLT entries detected! > ld: Unexpected run-time procedure linkages detected! > > Adding -fno-pie to this command doesn't fix the problem. > > Note that when cross-building with a GCC 10.2 and binutils 2.35.1 I also > get several "aarch64-linux-gnu-ld: warning: -z norelro ignored" in > addition to the error, but I don't get that warning with the 8.3.0 > toolchain. Thanks, my config (renesas_defconfig) also had CONFIG_MODULES disabled. Enabling that fixes the link error due to unexpected entries, but the .eh_frame orphan section warning is still there. Gr{oetje,eeting}s, Geert
On Tue, 27 Oct 2020 at 11:20, Geert Uytterhoeven <geert@linux-m68k.org> wrote: > > Hi Jean-Philippe, > > On Tue, Oct 27, 2020 at 11:09 AM Jean-Philippe Brucker > <jean-philippe@linaro.org> wrote: > > On Mon, Oct 26, 2020 at 06:38:46PM +0100, Ard Biesheuvel wrote: > > > > > > Note that even on plain be2881824ae9eb92, I get: > > > > > > > > > > > > aarch64-linux-gnu-ld: Unexpected GOT/PLT entries detected! > > > > > > aarch64-linux-gnu-ld: Unexpected run-time procedure linkages detected! > > > > > > > > > > > > The parent commit obviously doesn't show that (but probably still has > > > > > > the problem). > > > > > > > > Reverting both > > > > b3e5d80d0c48c0cc ("arm64/build: Warn on orphan section placement") > > > > be2881824ae9eb92 ("arm64/build: Assert for unwanted sections") > > > > seems to solve my problems, without any ill effects? > > > > > > > > > > I cannot reproduce the issue here with my distro GCC+binutils (Debian 8.3.0) > > > > I have the same problem with one of my debug configs and Linux v5.10-rc1, > > and can reproduce with the Debian 8.3.0 toolchain, by using the arm64 > > defconfig and disabling CONFIG_MODULES: > > > > ld -EL -maarch64elf --no-undefined -X -z norelro -shared -Bsymbolic -z notext --no-apply-dynamic-relocs --fix-cortex-a53-843419 --orphan-handling=warn --build-id=sha1 --strip-debug -o .tmp_vmlinux.kallsyms1 -T ./arch/arm64/kernel/vmlinux.lds --whole-archive arch/arm64/kernel/head.o init/built-in.a usr/built-in.a arch/arm64/built-in.a kernel/built-in.a certs/built-in.a mm/built-in.a fs/built-in.a ipc/built-in.a security/built-in.a crypto/built-in.a block/built-in.a arch/arm64/lib/built-in.a lib/built-in.a drivers/built-in.a sound/built-in.a net/built-in.a virt/built-in.a --no-whole-archive --start-group arch/arm64/lib/lib.a lib/lib.a ./drivers/firmware/efi/libstub/lib.a --end-group > > ld: Unexpected GOT/PLT entries detected! > > ld: Unexpected run-time procedure linkages detected! > > > > Adding -fno-pie to this command doesn't fix the problem. > > > > Note that when cross-building with a GCC 10.2 and binutils 2.35.1 I also > > get several "aarch64-linux-gnu-ld: warning: -z norelro ignored" in > > addition to the error, but I don't get that warning with the 8.3.0 > > toolchain. > > Thanks, my config (renesas_defconfig) also had CONFIG_MODULES disabled. > Enabling that fixes the link error due to unexpected entries, but the > .eh_frame orphan section warning is still there. > Looks like this is caused by the VFIO driver doing nasty things with symbol_get(), resulting in weak symbol references being emitted. Since taking the address of a weak symbol can yield NULL, the only way for the linker to accommodate this is to use GOT indirection for the direct symbol reference, so that the GOT entry can be set to NULL if the reference is not satisfied at link time.
On Tue, 27 Oct 2020 at 17:00, Ard Biesheuvel <ardb@kernel.org> wrote: > > On Tue, 27 Oct 2020 at 11:20, Geert Uytterhoeven <geert@linux-m68k.org> wrote: > > > > Hi Jean-Philippe, > > > > On Tue, Oct 27, 2020 at 11:09 AM Jean-Philippe Brucker > > <jean-philippe@linaro.org> wrote: > > > On Mon, Oct 26, 2020 at 06:38:46PM +0100, Ard Biesheuvel wrote: > > > > > > > Note that even on plain be2881824ae9eb92, I get: > > > > > > > > > > > > > > aarch64-linux-gnu-ld: Unexpected GOT/PLT entries detected! > > > > > > > aarch64-linux-gnu-ld: Unexpected run-time procedure linkages detected! > > > > > > > > > > > > > > The parent commit obviously doesn't show that (but probably still has > > > > > > > the problem). > > > > > > > > > > Reverting both > > > > > b3e5d80d0c48c0cc ("arm64/build: Warn on orphan section placement") > > > > > be2881824ae9eb92 ("arm64/build: Assert for unwanted sections") > > > > > seems to solve my problems, without any ill effects? > > > > > > > > > > > > > I cannot reproduce the issue here with my distro GCC+binutils (Debian 8.3.0) > > > > > > I have the same problem with one of my debug configs and Linux v5.10-rc1, > > > and can reproduce with the Debian 8.3.0 toolchain, by using the arm64 > > > defconfig and disabling CONFIG_MODULES: > > > > > > ld -EL -maarch64elf --no-undefined -X -z norelro -shared -Bsymbolic -z notext --no-apply-dynamic-relocs --fix-cortex-a53-843419 --orphan-handling=warn --build-id=sha1 --strip-debug -o .tmp_vmlinux.kallsyms1 -T ./arch/arm64/kernel/vmlinux.lds --whole-archive arch/arm64/kernel/head.o init/built-in.a usr/built-in.a arch/arm64/built-in.a kernel/built-in.a certs/built-in.a mm/built-in.a fs/built-in.a ipc/built-in.a security/built-in.a crypto/built-in.a block/built-in.a arch/arm64/lib/built-in.a lib/built-in.a drivers/built-in.a sound/built-in.a net/built-in.a virt/built-in.a --no-whole-archive --start-group arch/arm64/lib/lib.a lib/lib.a ./drivers/firmware/efi/libstub/lib.a --end-group > > > ld: Unexpected GOT/PLT entries detected! > > > ld: Unexpected run-time procedure linkages detected! ld: Unexpected GOT/PLT entries detected! ld: Unexpected run-time procedure linkages detected! The arm64 build error fixed by (I have tested defconfig) [PATCH] soc: qcom: QCOM_RPMH fix build with modular QCOM_RPMH https://lore.kernel.org/linux-arm-msm/20201027111422.4008114-1-anders.roxell@linaro.org/ --- When building allmodconfig leading to the following link error with CONFIG_QCOM_RPMH=y and CONFIG_QCOM_COMMAND_DB=m: aarch64-linux-gnu-ld: drivers/clk/qcom/clk-rpmh.o: in function `clk_rpmh_probe': drivers/clk/qcom/clk-rpmh.c:474: undefined reference to `cmd_db_read_addr' drivers/clk/qcom/clk-rpmh.c:474:(.text+0x254): relocation truncated to fit: R_AARCH64_CALL26 against undefined symbol `cmd_db_read_addr' Fix this by adding a Kconfig depenency and forcing QCOM_RPMH to be a module when QCOM_COMMAND_DB is a module. Also removing the dependency on 'ARCH_QCOM || COMPILE_TEST' since that is already a dependency for QCOM_COMMAND_DB. Fixes: 778279f4f5e4 ("soc: qcom: cmd-db: allow loading as a module") Signed-off-by: Anders Roxell <anders.roxell@linaro.org> --- drivers/soc/qcom/Kconfig | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/drivers/soc/qcom/Kconfig b/drivers/soc/qcom/Kconfig index 9b4ae9c16ba7..3bdd1604f78f 100644 --- a/drivers/soc/qcom/Kconfig +++ b/drivers/soc/qcom/Kconfig @@ -109,7 +109,7 @@ config QCOM_RMTFS_MEM config QCOM_RPMH tristate "Qualcomm RPM-Hardened (RPMH) Communication" - depends on ARCH_QCOM || COMPILE_TEST + depends on QCOM_COMMAND_DB help Support for communication with the hardened-RPM blocks in Qualcomm Technologies Inc (QTI) SoCs. RPMH communication uses an
On Tue, 27 Oct 2020 at 12:29, Ard Biesheuvel <ardb@kernel.org> wrote: > > On Tue, 27 Oct 2020 at 11:20, Geert Uytterhoeven <geert@linux-m68k.org> wrote: > > > > Hi Jean-Philippe, > > > > On Tue, Oct 27, 2020 at 11:09 AM Jean-Philippe Brucker > > <jean-philippe@linaro.org> wrote: > > > On Mon, Oct 26, 2020 at 06:38:46PM +0100, Ard Biesheuvel wrote: > > > > > > > Note that even on plain be2881824ae9eb92, I get: > > > > > > > > > > > > > > aarch64-linux-gnu-ld: Unexpected GOT/PLT entries detected! > > > > > > > aarch64-linux-gnu-ld: Unexpected run-time procedure linkages detected! > > > > > > > > > > > > > > The parent commit obviously doesn't show that (but probably still has > > > > > > > the problem). > > > > > > > > > > Reverting both > > > > > b3e5d80d0c48c0cc ("arm64/build: Warn on orphan section placement") > > > > > be2881824ae9eb92 ("arm64/build: Assert for unwanted sections") > > > > > seems to solve my problems, without any ill effects? > > > > > > > > > > > > > I cannot reproduce the issue here with my distro GCC+binutils (Debian 8.3.0) > > > > > > I have the same problem with one of my debug configs and Linux v5.10-rc1, > > > and can reproduce with the Debian 8.3.0 toolchain, by using the arm64 > > > defconfig and disabling CONFIG_MODULES: > > > > > > ld -EL -maarch64elf --no-undefined -X -z norelro -shared -Bsymbolic -z notext --no-apply-dynamic-relocs --fix-cortex-a53-843419 --orphan-handling=warn --build-id=sha1 --strip-debug -o .tmp_vmlinux.kallsyms1 -T ./arch/arm64/kernel/vmlinux.lds --whole-archive arch/arm64/kernel/head.o init/built-in.a usr/built-in.a arch/arm64/built-in.a kernel/built-in.a certs/built-in.a mm/built-in.a fs/built-in.a ipc/built-in.a security/built-in.a crypto/built-in.a block/built-in.a arch/arm64/lib/built-in.a lib/built-in.a drivers/built-in.a sound/built-in.a net/built-in.a virt/built-in.a --no-whole-archive --start-group arch/arm64/lib/lib.a lib/lib.a ./drivers/firmware/efi/libstub/lib.a --end-group > > > ld: Unexpected GOT/PLT entries detected! > > > ld: Unexpected run-time procedure linkages detected! > > > > > > Adding -fno-pie to this command doesn't fix the problem. > > > > > > Note that when cross-building with a GCC 10.2 and binutils 2.35.1 I also > > > get several "aarch64-linux-gnu-ld: warning: -z norelro ignored" in > > > addition to the error, but I don't get that warning with the 8.3.0 > > > toolchain. > > > > Thanks, my config (renesas_defconfig) also had CONFIG_MODULES disabled. > > Enabling that fixes the link error due to unexpected entries, but the > > .eh_frame orphan section warning is still there. > > > > Looks like this is caused by the VFIO driver doing nasty things with > symbol_get(), resulting in weak symbol references being emitted. Since > taking the address of a weak symbol can yield NULL, the only way for > the linker to accommodate this is to use GOT indirection for the > direct symbol reference, so that the GOT entry can be set to NULL if > the reference is not satisfied at link time. This seems to do the trick for me. diff --git a/include/linux/module.h b/include/linux/module.h index 7ccdf87f376f..6264617bab4d 100644 --- a/include/linux/module.h +++ b/include/linux/module.h @@ -740,7 +740,7 @@ static inline bool within_module(unsigned long addr, const struct module *mod) } /* Get/put a kernel symbol (calls should be symmetric) */ -#define symbol_get(x) ({ extern typeof(x) x __attribute__((weak)); &(x); }) +#define symbol_get(x) ({ extern typeof(x) x __attribute__((weak,visibility("hidden"))); &(x); }) #define symbol_put(x) do { } while (0) #define symbol_put_addr(x) do { } while (0)
Hi Nick, CC Josh On Mon, Oct 26, 2020 at 6:49 PM Nick Desaulniers <ndesaulniers@google.com> wrote: > On Mon, Oct 26, 2020 at 10:44 AM Geert Uytterhoeven > <geert@linux-m68k.org> wrote: > > On Mon, Oct 26, 2020 at 6:39 PM Ard Biesheuvel <ardb@kernel.org> wrote: > > > On Mon, 26 Oct 2020 at 17:01, Geert Uytterhoeven <geert@linux-m68k.org> wrote: > > > > On Mon, Oct 26, 2020 at 2:29 PM Geert Uytterhoeven <geert@linux-m68k.org> wrote: > > > > > On Mon, Oct 26, 2020 at 1:29 PM Geert Uytterhoeven <geert@linux-m68k.org> wrote: > > > > > > On Fri, Aug 21, 2020 at 9:56 PM Kees Cook <keescook@chromium.org> wrote: > > > > > > > In preparation for warning on orphan sections, discard > > > > > > > unwanted non-zero-sized generated sections, and enforce other > > > > > > > expected-to-be-zero-sized sections (since discarding them might hide > > > > > > > problems with them suddenly gaining unexpected entries). > > > > > > > > > > > > > > Suggested-by: Ard Biesheuvel <ardb@kernel.org> > > > > > > > Signed-off-by: Kees Cook <keescook@chromium.org> > > > > > > > > > > > > This is now commit be2881824ae9eb92 ("arm64/build: Assert for unwanted > > > > > > sections") in v5.10-rc1, and is causing the following error with > > > > > > renesas_defconfig[1]: > > > > > > > > > > > > aarch64-linux-gnu-ld: warning: orphan section `.eh_frame' from > > > > > > `kernel/bpf/core.o' being placed in section `.eh_frame' > > > > > > aarch64-linux-gnu-ld: Unexpected GOT/PLT entries detected! > > > > > > aarch64-linux-gnu-ld: Unexpected run-time procedure linkages detected! > > > > > > > > > > > > I cannot reproduce this with the standard arm64 defconfig. > > > > > > > > > > > > I bisected the error to the aforementioned commit, but understand this > > > > > > is not the real reason. If I revert this commit, I still get: > > > > > > > > > > > > aarch64-linux-gnu-ld: warning: orphan section `.got.plt' from > > > > > > `arch/arm64/kernel/head.o' being placed in section `.got.plt' > > > > > > aarch64-linux-gnu-ld: warning: orphan section `.plt' from > > > > > > `arch/arm64/kernel/head.o' being placed in section `.plt' > > > > > > aarch64-linux-gnu-ld: warning: orphan section `.data.rel.ro' from > > > > > > `arch/arm64/kernel/head.o' being placed in section `.data.rel.ro' > > > > > > aarch64-linux-gnu-ld: warning: orphan section `.eh_frame' from > > > > > > `kernel/bpf/core.o' being placed in section `.eh_frame' > > > > > > > > > > > > I.e. including the ".eh_frame" warning. I have tried bisecting that > > > > > > warning (i.e. with be2881824ae9eb92 reverted), but that leads me to > > > > > > commit b3e5d80d0c48c0cc ("arm64/build: Warn on orphan section > > > > > > placement"), which is another red herring. > > > > > > > > > > kernel/bpf/core.o is the only file containing an eh_frame section, > > > > > causing the warning. > > When I see .eh_frame, I think -fno-asynchronous-unwind-tables is > missing from someone's KBUILD_CFLAGS. > But I don't see anything curious in kernel/bpf/Makefile, unless > cc-disable-warning is somehow broken. I tracked it down to kernel/bpf/core.c:___bpf_prog_run() being tagged with __no_fgcse aka __attribute__((optimize("-fno-gcse"))). Even if the function is trivially empty ("return 0;"), a ".eh_frame" section is generated. Removing the __no_fgcse tag fixes that. Gr{oetje,eeting}s, Geert
On Tue, 27 Oct 2020 at 20:25, Geert Uytterhoeven <geert@linux-m68k.org> wrote: > > Hi Nick, > > CC Josh > > On Mon, Oct 26, 2020 at 6:49 PM Nick Desaulniers > <ndesaulniers@google.com> wrote: > > On Mon, Oct 26, 2020 at 10:44 AM Geert Uytterhoeven > > <geert@linux-m68k.org> wrote: > > > On Mon, Oct 26, 2020 at 6:39 PM Ard Biesheuvel <ardb@kernel.org> wrote: > > > > On Mon, 26 Oct 2020 at 17:01, Geert Uytterhoeven <geert@linux-m68k.org> wrote: > > > > > On Mon, Oct 26, 2020 at 2:29 PM Geert Uytterhoeven <geert@linux-m68k.org> wrote: > > > > > > On Mon, Oct 26, 2020 at 1:29 PM Geert Uytterhoeven <geert@linux-m68k.org> wrote: > > > > > > > On Fri, Aug 21, 2020 at 9:56 PM Kees Cook <keescook@chromium.org> wrote: > > > > > > > > In preparation for warning on orphan sections, discard > > > > > > > > unwanted non-zero-sized generated sections, and enforce other > > > > > > > > expected-to-be-zero-sized sections (since discarding them might hide > > > > > > > > problems with them suddenly gaining unexpected entries). > > > > > > > > > > > > > > > > Suggested-by: Ard Biesheuvel <ardb@kernel.org> > > > > > > > > Signed-off-by: Kees Cook <keescook@chromium.org> > > > > > > > > > > > > > > This is now commit be2881824ae9eb92 ("arm64/build: Assert for unwanted > > > > > > > sections") in v5.10-rc1, and is causing the following error with > > > > > > > renesas_defconfig[1]: > > > > > > > > > > > > > > aarch64-linux-gnu-ld: warning: orphan section `.eh_frame' from > > > > > > > `kernel/bpf/core.o' being placed in section `.eh_frame' > > > > > > > aarch64-linux-gnu-ld: Unexpected GOT/PLT entries detected! > > > > > > > aarch64-linux-gnu-ld: Unexpected run-time procedure linkages detected! > > > > > > > > > > > > > > I cannot reproduce this with the standard arm64 defconfig. > > > > > > > > > > > > > > I bisected the error to the aforementioned commit, but understand this > > > > > > > is not the real reason. If I revert this commit, I still get: > > > > > > > > > > > > > > aarch64-linux-gnu-ld: warning: orphan section `.got.plt' from > > > > > > > `arch/arm64/kernel/head.o' being placed in section `.got.plt' > > > > > > > aarch64-linux-gnu-ld: warning: orphan section `.plt' from > > > > > > > `arch/arm64/kernel/head.o' being placed in section `.plt' > > > > > > > aarch64-linux-gnu-ld: warning: orphan section `.data.rel.ro' from > > > > > > > `arch/arm64/kernel/head.o' being placed in section `.data.rel.ro' > > > > > > > aarch64-linux-gnu-ld: warning: orphan section `.eh_frame' from > > > > > > > `kernel/bpf/core.o' being placed in section `.eh_frame' > > > > > > > > > > > > > > I.e. including the ".eh_frame" warning. I have tried bisecting that > > > > > > > warning (i.e. with be2881824ae9eb92 reverted), but that leads me to > > > > > > > commit b3e5d80d0c48c0cc ("arm64/build: Warn on orphan section > > > > > > > placement"), which is another red herring. > > > > > > > > > > > > kernel/bpf/core.o is the only file containing an eh_frame section, > > > > > > causing the warning. > > > > When I see .eh_frame, I think -fno-asynchronous-unwind-tables is > > missing from someone's KBUILD_CFLAGS. > > But I don't see anything curious in kernel/bpf/Makefile, unless > > cc-disable-warning is somehow broken. > > I tracked it down to kernel/bpf/core.c:___bpf_prog_run() being tagged > with __no_fgcse aka __attribute__((optimize("-fno-gcse"))). > > Even if the function is trivially empty ("return 0;"), a ".eh_frame" section > is generated. Removing the __no_fgcse tag fixes that. > Given that it was added for issues related to retpolines, ORC and objtool, it should be safe to make that annotation x86-only.
On Tue, Oct 27, 2020 at 08:33:00PM +0100, Ard Biesheuvel wrote: > On Tue, 27 Oct 2020 at 20:25, Geert Uytterhoeven <geert@linux-m68k.org> wrote: > > > > > > When I see .eh_frame, I think -fno-asynchronous-unwind-tables is > > > missing from someone's KBUILD_CFLAGS. > > > But I don't see anything curious in kernel/bpf/Makefile, unless > > > cc-disable-warning is somehow broken. > > > > I tracked it down to kernel/bpf/core.c:___bpf_prog_run() being tagged > > with __no_fgcse aka __attribute__((optimize("-fno-gcse"))). > > > > Even if the function is trivially empty ("return 0;"), a ".eh_frame" section > > is generated. Removing the __no_fgcse tag fixes that. > > > > > Given that it was added for issues related to retpolines, ORC and > objtool, it should be safe to make that annotation x86-only. The optimize attribute is not meant for production use. I had mentioned this at the time but it got lost: the optimize attribute apparently does not add options, it replaces them completely. So I'm guessing this one is dropping the -fno-asynchronous-unwind-tables and causing the eh_frame sections, though I don't know why that doesn't cause eh_frame on x86? https://lore.kernel.org/lkml/alpine.LSU.2.21.2004151445520.11688@wotan.suse.de/
On Tue, Oct 27, 2020 at 12:25 PM Geert Uytterhoeven <geert@linux-m68k.org> wrote: > > Hi Nick, > > CC Josh > > On Mon, Oct 26, 2020 at 6:49 PM Nick Desaulniers > <ndesaulniers@google.com> wrote: > > On Mon, Oct 26, 2020 at 10:44 AM Geert Uytterhoeven > > <geert@linux-m68k.org> wrote: > > > On Mon, Oct 26, 2020 at 6:39 PM Ard Biesheuvel <ardb@kernel.org> wrote: > > > > On Mon, 26 Oct 2020 at 17:01, Geert Uytterhoeven <geert@linux-m68k.org> wrote: > > > > > On Mon, Oct 26, 2020 at 2:29 PM Geert Uytterhoeven <geert@linux-m68k.org> wrote: > > > > > > On Mon, Oct 26, 2020 at 1:29 PM Geert Uytterhoeven <geert@linux-m68k.org> wrote: > > > > > > > I.e. including the ".eh_frame" warning. I have tried bisecting that > > > > > > > warning (i.e. with be2881824ae9eb92 reverted), but that leads me to > > > > > > > commit b3e5d80d0c48c0cc ("arm64/build: Warn on orphan section > > > > > > > placement"), which is another red herring. > > > > > > > > > > > > kernel/bpf/core.o is the only file containing an eh_frame section, > > > > > > causing the warning. > > > > When I see .eh_frame, I think -fno-asynchronous-unwind-tables is > > missing from someone's KBUILD_CFLAGS. > > But I don't see anything curious in kernel/bpf/Makefile, unless > > cc-disable-warning is somehow broken. > > I tracked it down to kernel/bpf/core.c:___bpf_prog_run() being tagged > with __no_fgcse aka __attribute__((optimize("-fno-gcse"))). > > Even if the function is trivially empty ("return 0;"), a ".eh_frame" section > is generated. Removing the __no_fgcse tag fixes that. That's weird. I feel pretty strongly that unless we're working around a well understood compiler bug with a comment that links to a submitted bug report, turning off rando compiler optimizations is a terrible hack for which one must proceed straight to jail; do not pass go; do not collect $200. But maybe I'd feel differently for this case given the context of the change that added it. (Ard mentions retpolines+orc+objtool; can someone share the relevant SHA if you have it handy so I don't have to go digging?) (I feel the same about there being an empty asm(); statement in the definition of asm_volatile_goto for compiler-gcc.h). Might be time to "fix the compiler." (It sounds like Arvind is both in agreement with my sentiment, and has the root cause). -- Thanks, ~Nick Desaulniers
On Tue, 27 Oct 2020 at 21:12, Nick Desaulniers <ndesaulniers@google.com> wrote: > > On Tue, Oct 27, 2020 at 12:25 PM Geert Uytterhoeven > <geert@linux-m68k.org> wrote: > > > > Hi Nick, > > > > CC Josh > > > > On Mon, Oct 26, 2020 at 6:49 PM Nick Desaulniers > > <ndesaulniers@google.com> wrote: > > > On Mon, Oct 26, 2020 at 10:44 AM Geert Uytterhoeven > > > <geert@linux-m68k.org> wrote: > > > > On Mon, Oct 26, 2020 at 6:39 PM Ard Biesheuvel <ardb@kernel.org> wrote: > > > > > On Mon, 26 Oct 2020 at 17:01, Geert Uytterhoeven <geert@linux-m68k.org> wrote: > > > > > > On Mon, Oct 26, 2020 at 2:29 PM Geert Uytterhoeven <geert@linux-m68k.org> wrote: > > > > > > > On Mon, Oct 26, 2020 at 1:29 PM Geert Uytterhoeven <geert@linux-m68k.org> wrote: > > > > > > > > I.e. including the ".eh_frame" warning. I have tried bisecting that > > > > > > > > warning (i.e. with be2881824ae9eb92 reverted), but that leads me to > > > > > > > > commit b3e5d80d0c48c0cc ("arm64/build: Warn on orphan section > > > > > > > > placement"), which is another red herring. > > > > > > > > > > > > > > kernel/bpf/core.o is the only file containing an eh_frame section, > > > > > > > causing the warning. > > > > > > When I see .eh_frame, I think -fno-asynchronous-unwind-tables is > > > missing from someone's KBUILD_CFLAGS. > > > But I don't see anything curious in kernel/bpf/Makefile, unless > > > cc-disable-warning is somehow broken. > > > > I tracked it down to kernel/bpf/core.c:___bpf_prog_run() being tagged > > with __no_fgcse aka __attribute__((optimize("-fno-gcse"))). > > > > Even if the function is trivially empty ("return 0;"), a ".eh_frame" section > > is generated. Removing the __no_fgcse tag fixes that. > > That's weird. I feel pretty strongly that unless we're working around > a well understood compiler bug with a comment that links to a > submitted bug report, turning off rando compiler optimizations is a > terrible hack for which one must proceed straight to jail; do not pass > go; do not collect $200. But maybe I'd feel differently for this case > given the context of the change that added it. (Ard mentions > retpolines+orc+objtool; can someone share the relevant SHA if you have > it handy so I don't have to go digging?) commit 3193c0836f203a91bef96d88c64cccf0be090d9c Author: Josh Poimboeuf <jpoimboe@redhat.com> Date: Wed Jul 17 20:36:45 2019 -0500 bpf: Disable GCC -fgcse optimization for ___bpf_prog_run() has Fixes: e55a73251da3 ("bpf: Fix ORC unwinding in non-JIT BPF code") and mentions objtool and CONFIG_RETPOLINE. > (I feel the same about there > being an empty asm(); statement in the definition of asm_volatile_goto > for compiler-gcc.h). Might be time to "fix the compiler." > > (It sounds like Arvind is both in agreement with my sentiment, and has > the root cause). > I agree that the __no_fgcse hack is terrible. Does Clang support the following pragmas? #pragma GCC push_options #pragma GCC optimize ("-fno-gcse") #pragma GCC pop_options ?
On Tue, Oct 27, 2020 at 1:15 PM Ard Biesheuvel <ardb@kernel.org> wrote: > > On Tue, 27 Oct 2020 at 21:12, Nick Desaulniers <ndesaulniers@google.com> wrote: > > > > On Tue, Oct 27, 2020 at 12:25 PM Geert Uytterhoeven > > <geert@linux-m68k.org> wrote: > > > > > > Hi Nick, > > > > > > CC Josh > > > > > > On Mon, Oct 26, 2020 at 6:49 PM Nick Desaulniers > > > <ndesaulniers@google.com> wrote: > > > > On Mon, Oct 26, 2020 at 10:44 AM Geert Uytterhoeven > > > > <geert@linux-m68k.org> wrote: > > > > > On Mon, Oct 26, 2020 at 6:39 PM Ard Biesheuvel <ardb@kernel.org> wrote: > > > > > > On Mon, 26 Oct 2020 at 17:01, Geert Uytterhoeven <geert@linux-m68k.org> wrote: > > > > > > > On Mon, Oct 26, 2020 at 2:29 PM Geert Uytterhoeven <geert@linux-m68k.org> wrote: > > > > > > > > On Mon, Oct 26, 2020 at 1:29 PM Geert Uytterhoeven <geert@linux-m68k.org> wrote: > > > > > > > > > I.e. including the ".eh_frame" warning. I have tried bisecting that > > > > > > > > > warning (i.e. with be2881824ae9eb92 reverted), but that leads me to > > > > > > > > > commit b3e5d80d0c48c0cc ("arm64/build: Warn on orphan section > > > > > > > > > placement"), which is another red herring. > > > > > > > > > > > > > > > > kernel/bpf/core.o is the only file containing an eh_frame section, > > > > > > > > causing the warning. > > > > > > > > When I see .eh_frame, I think -fno-asynchronous-unwind-tables is > > > > missing from someone's KBUILD_CFLAGS. > > > > But I don't see anything curious in kernel/bpf/Makefile, unless > > > > cc-disable-warning is somehow broken. > > > > > > I tracked it down to kernel/bpf/core.c:___bpf_prog_run() being tagged > > > with __no_fgcse aka __attribute__((optimize("-fno-gcse"))). > > > > > > Even if the function is trivially empty ("return 0;"), a ".eh_frame" section > > > is generated. Removing the __no_fgcse tag fixes that. > > > > That's weird. I feel pretty strongly that unless we're working around > > a well understood compiler bug with a comment that links to a > > submitted bug report, turning off rando compiler optimizations is a > > terrible hack for which one must proceed straight to jail; do not pass > > go; do not collect $200. But maybe I'd feel differently for this case > > given the context of the change that added it. (Ard mentions > > retpolines+orc+objtool; can someone share the relevant SHA if you have > > it handy so I don't have to go digging?) > > commit 3193c0836f203a91bef96d88c64cccf0be090d9c > Author: Josh Poimboeuf <jpoimboe@redhat.com> > Date: Wed Jul 17 20:36:45 2019 -0500 > > bpf: Disable GCC -fgcse optimization for ___bpf_prog_run() > > has > > Fixes: e55a73251da3 ("bpf: Fix ORC unwinding in non-JIT BPF code") > > and mentions objtool and CONFIG_RETPOLINE. > > > (I feel the same about there > > being an empty asm(); statement in the definition of asm_volatile_goto > > for compiler-gcc.h). Might be time to "fix the compiler." > > > > (It sounds like Arvind is both in agreement with my sentiment, and has > > the root cause). > > > > I agree that the __no_fgcse hack is terrible. Does Clang support the > following pragmas? > > #pragma GCC push_options > #pragma GCC optimize ("-fno-gcse") > #pragma GCC pop_options > > ? Put it in godbolt.org. Pretty sure it's `#pragma clang` though. `#pragma GCC` might be supported in clang or silently ignored, but IIRC pragmas were a bit of a compat nightmare. I think Arnd wrote some macros to set pragmas based on toolchain. (Uses _Pragma, for pragmas in macros, IIRC).
(+ right linux-toolchains mailing list, apologies for adding the wrong one, I'm forever doomed to have gmail autocomplete to the wrong one now that I've sent to it before) On Tue, Oct 27, 2020 at 1:15 PM Ard Biesheuvel <ardb@kernel.org> wrote: > > On Tue, 27 Oct 2020 at 21:12, Nick Desaulniers <ndesaulniers@google.com> wrote: > > > > On Tue, Oct 27, 2020 at 12:25 PM Geert Uytterhoeven > > <geert@linux-m68k.org> wrote: > > > > > > Hi Nick, > > > > > > CC Josh > > > > > > On Mon, Oct 26, 2020 at 6:49 PM Nick Desaulniers > > > <ndesaulniers@google.com> wrote: > > > > On Mon, Oct 26, 2020 at 10:44 AM Geert Uytterhoeven > > > > <geert@linux-m68k.org> wrote: > > > > > On Mon, Oct 26, 2020 at 6:39 PM Ard Biesheuvel <ardb@kernel.org> wrote: > > > > > > On Mon, 26 Oct 2020 at 17:01, Geert Uytterhoeven <geert@linux-m68k.org> wrote: > > > > > > > On Mon, Oct 26, 2020 at 2:29 PM Geert Uytterhoeven <geert@linux-m68k.org> wrote: > > > > > > > > On Mon, Oct 26, 2020 at 1:29 PM Geert Uytterhoeven <geert@linux-m68k.org> wrote: > > > > > > > > > I.e. including the ".eh_frame" warning. I have tried bisecting that > > > > > > > > > warning (i.e. with be2881824ae9eb92 reverted), but that leads me to > > > > > > > > > commit b3e5d80d0c48c0cc ("arm64/build: Warn on orphan section > > > > > > > > > placement"), which is another red herring. > > > > > > > > > > > > > > > > kernel/bpf/core.o is the only file containing an eh_frame section, > > > > > > > > causing the warning. > > > > > > > > When I see .eh_frame, I think -fno-asynchronous-unwind-tables is > > > > missing from someone's KBUILD_CFLAGS. > > > > But I don't see anything curious in kernel/bpf/Makefile, unless > > > > cc-disable-warning is somehow broken. > > > > > > I tracked it down to kernel/bpf/core.c:___bpf_prog_run() being tagged > > > with __no_fgcse aka __attribute__((optimize("-fno-gcse"))). > > > > > > Even if the function is trivially empty ("return 0;"), a ".eh_frame" section > > > is generated. Removing the __no_fgcse tag fixes that. > > > > That's weird. I feel pretty strongly that unless we're working around > > a well understood compiler bug with a comment that links to a > > submitted bug report, turning off rando compiler optimizations is a > > terrible hack for which one must proceed straight to jail; do not pass > > go; do not collect $200. But maybe I'd feel differently for this case > > given the context of the change that added it. (Ard mentions > > retpolines+orc+objtool; can someone share the relevant SHA if you have > > it handy so I don't have to go digging?) > > commit 3193c0836f203a91bef96d88c64cccf0be090d9c > Author: Josh Poimboeuf <jpoimboe@redhat.com> > Date: Wed Jul 17 20:36:45 2019 -0500 > > bpf: Disable GCC -fgcse optimization for ___bpf_prog_run() > > has > > Fixes: e55a73251da3 ("bpf: Fix ORC unwinding in non-JIT BPF code") > > and mentions objtool and CONFIG_RETPOLINE. Thanks for the context. It might be time to revisit the above commit. If I revert it (small conflict that's easy to fixup), kernel/bpf/core.o builds cleanly with defconfig+GCC-9.3, so maybe obtool did get smart enough to handle that case? Probably regresses the performance of that main dispatch loop for BPF, but not sure what folks are expecting when retpolines are enabled.
On Tue, Oct 27, 2020 at 01:17:55PM -0700, Nick Desaulniers wrote: > On Tue, Oct 27, 2020 at 1:15 PM Ard Biesheuvel <ardb@kernel.org> wrote: > > > > On Tue, 27 Oct 2020 at 21:12, Nick Desaulniers <ndesaulniers@google.com> wrote: > > > > > > On Tue, Oct 27, 2020 at 12:25 PM Geert Uytterhoeven > > > <geert@linux-m68k.org> wrote: > > > > > > > > Hi Nick, > > > > > > > > CC Josh > > > > > > > > On Mon, Oct 26, 2020 at 6:49 PM Nick Desaulniers > > > > <ndesaulniers@google.com> wrote: > > > > > On Mon, Oct 26, 2020 at 10:44 AM Geert Uytterhoeven > > > > > <geert@linux-m68k.org> wrote: > > > > > > On Mon, Oct 26, 2020 at 6:39 PM Ard Biesheuvel <ardb@kernel.org> wrote: > > > > > > > On Mon, 26 Oct 2020 at 17:01, Geert Uytterhoeven <geert@linux-m68k.org> wrote: > > > > > > > > On Mon, Oct 26, 2020 at 2:29 PM Geert Uytterhoeven <geert@linux-m68k.org> wrote: > > > > > > > > > On Mon, Oct 26, 2020 at 1:29 PM Geert Uytterhoeven <geert@linux-m68k.org> wrote: > > > > > > > > > > I.e. including the ".eh_frame" warning. I have tried bisecting that > > > > > > > > > > warning (i.e. with be2881824ae9eb92 reverted), but that leads me to > > > > > > > > > > commit b3e5d80d0c48c0cc ("arm64/build: Warn on orphan section > > > > > > > > > > placement"), which is another red herring. > > > > > > > > > > > > > > > > > > kernel/bpf/core.o is the only file containing an eh_frame section, > > > > > > > > > causing the warning. > > > > > > > > > > When I see .eh_frame, I think -fno-asynchronous-unwind-tables is > > > > > missing from someone's KBUILD_CFLAGS. > > > > > But I don't see anything curious in kernel/bpf/Makefile, unless > > > > > cc-disable-warning is somehow broken. > > > > > > > > I tracked it down to kernel/bpf/core.c:___bpf_prog_run() being tagged > > > > with __no_fgcse aka __attribute__((optimize("-fno-gcse"))). > > > > > > > > Even if the function is trivially empty ("return 0;"), a ".eh_frame" section > > > > is generated. Removing the __no_fgcse tag fixes that. > > > > > > That's weird. I feel pretty strongly that unless we're working around > > > a well understood compiler bug with a comment that links to a > > > submitted bug report, turning off rando compiler optimizations is a > > > terrible hack for which one must proceed straight to jail; do not pass > > > go; do not collect $200. But maybe I'd feel differently for this case > > > given the context of the change that added it. (Ard mentions > > > retpolines+orc+objtool; can someone share the relevant SHA if you have > > > it handy so I don't have to go digging?) > > > > commit 3193c0836f203a91bef96d88c64cccf0be090d9c > > Author: Josh Poimboeuf <jpoimboe@redhat.com> > > Date: Wed Jul 17 20:36:45 2019 -0500 > > > > bpf: Disable GCC -fgcse optimization for ___bpf_prog_run() > > > > has > > > > Fixes: e55a73251da3 ("bpf: Fix ORC unwinding in non-JIT BPF code") > > > > and mentions objtool and CONFIG_RETPOLINE. > > > > > (I feel the same about there > > > being an empty asm(); statement in the definition of asm_volatile_goto > > > for compiler-gcc.h). Might be time to "fix the compiler." > > > > > > (It sounds like Arvind is both in agreement with my sentiment, and has > > > the root cause). > > > > > > > I agree that the __no_fgcse hack is terrible. Does Clang support the > > following pragmas? > > > > #pragma GCC push_options > > #pragma GCC optimize ("-fno-gcse") > > #pragma GCC pop_options > > > > ? > > Put it in godbolt.org. Pretty sure it's `#pragma clang` though. > `#pragma GCC` might be supported in clang or silently ignored, but > IIRC pragmas were a bit of a compat nightmare. I think Arnd wrote > some macros to set pragmas based on toolchain. (Uses _Pragma, for > pragmas in macros, IIRC). > > -- > Thanks, > ~Nick Desaulniers https://gcc.gnu.org/onlinedocs/gcc/Function-Specific-Option-Pragmas.html#Function-Specific-Option-Pragmas #pragma GCC optimize is equivalent to the function attribute, so does that actually help? Btw, the bug mentioned in asm_volatile_goto seems like its been fixed in 4.9, so the hack could be dropped now?
On Tue, Oct 27, 2020 at 01:28:02PM -0700, Nick Desaulniers wrote: > > commit 3193c0836f203a91bef96d88c64cccf0be090d9c > > Author: Josh Poimboeuf <jpoimboe@redhat.com> > > Date: Wed Jul 17 20:36:45 2019 -0500 > > > > bpf: Disable GCC -fgcse optimization for ___bpf_prog_run() > > > > has > > > > Fixes: e55a73251da3 ("bpf: Fix ORC unwinding in non-JIT BPF code") > > > > and mentions objtool and CONFIG_RETPOLINE. > > Thanks for the context. It might be time to revisit the above commit. > If I revert it (small conflict that's easy to fixup), > kernel/bpf/core.o builds cleanly with defconfig+GCC-9.3, so maybe > obtool did get smart enough to handle that case? Probably regresses > the performance of that main dispatch loop for BPF, but not sure what > folks are expecting when retpolines are enabled. > -- > Thanks, > ~Nick Desaulniers The objtool issue was with RETPOLINE disabled.
On Tue, Oct 27, 2020 at 1:32 PM Arvind Sankar <nivedita@alum.mit.edu> wrote: > > On Tue, Oct 27, 2020 at 01:28:02PM -0700, Nick Desaulniers wrote: > > > commit 3193c0836f203a91bef96d88c64cccf0be090d9c > > > Author: Josh Poimboeuf <jpoimboe@redhat.com> > > > Date: Wed Jul 17 20:36:45 2019 -0500 > > > > > > bpf: Disable GCC -fgcse optimization for ___bpf_prog_run() > > > > > > has > > > > > > Fixes: e55a73251da3 ("bpf: Fix ORC unwinding in non-JIT BPF code") > > > > > > and mentions objtool and CONFIG_RETPOLINE. > > > > Thanks for the context. It might be time to revisit the above commit. > > If I revert it (small conflict that's easy to fixup), > > kernel/bpf/core.o builds cleanly with defconfig+GCC-9.3, so maybe > > obtool did get smart enough to handle that case? Probably regresses > > the performance of that main dispatch loop for BPF, but not sure what > > folks are expecting when retpolines are enabled. > > -- > > Thanks, > > ~Nick Desaulniers > > The objtool issue was with RETPOLINE disabled. Ah, sorry, in that case default-CONFIG_RETPOLINE+gcc-9.3: kernel/bpf/core.o: warning: objtool: ___bpf_prog_run()+0x8d4: sibling call from callable instruction with modified stack frame
On Tue, Oct 27, 2020 at 1:30 PM Arvind Sankar <nivedita@alum.mit.edu> wrote: > > On Tue, Oct 27, 2020 at 01:17:55PM -0700, Nick Desaulniers wrote: > > > > (I feel the same about there > > > > being an empty asm(); statement in the definition of asm_volatile_goto > > > > for compiler-gcc.h). Might be time to "fix the compiler." > > > > > > > > (It sounds like Arvind is both in agreement with my sentiment, and has > > > > the root cause). > > > > > Btw, the bug mentioned in asm_volatile_goto seems like its been fixed in > 4.9, so the hack could be dropped now? https://lore.kernel.org/lkml/20180907222109.163802-1-ndesaulniers@google.com/ For the life of me I can't find Linus' response. Maybe he shot it down in the PR, but I can't find it...Miguel do you recall? I could paraphrase, but might be better to not rely on my memory.
On Tue, Oct 27, 2020 at 01:40:43PM -0700, Nick Desaulniers wrote: > On Tue, Oct 27, 2020 at 1:30 PM Arvind Sankar <nivedita@alum.mit.edu> wrote: > > > > On Tue, Oct 27, 2020 at 01:17:55PM -0700, Nick Desaulniers wrote: > > > > > (I feel the same about there > > > > > being an empty asm(); statement in the definition of asm_volatile_goto > > > > > for compiler-gcc.h). Might be time to "fix the compiler." > > > > > > > > > > (It sounds like Arvind is both in agreement with my sentiment, and has > > > > > the root cause). > > > > > > > Btw, the bug mentioned in asm_volatile_goto seems like its been fixed in > > 4.9, so the hack could be dropped now? > > https://lore.kernel.org/lkml/20180907222109.163802-1-ndesaulniers@google.com/ > > For the life of me I can't find Linus' response. Maybe he shot it > down in the PR, but I can't find it...Miguel do you recall? I could > paraphrase, but might be better to not rely on my memory. > -- > Thanks, > ~Nick Desaulniers You couldn't find it in July either :) https://lkml.org/lkml/2020/7/10/1026 Possibly he didn't like the version check? That should be unnecessary now.
On Tue, Oct 27, 2020 at 09:15:17PM +0100, Ard Biesheuvel wrote: > On Tue, 27 Oct 2020 at 21:12, Nick Desaulniers <ndesaulniers@google.com> wrote: > > > > On Tue, Oct 27, 2020 at 12:25 PM Geert Uytterhoeven > > <geert@linux-m68k.org> wrote: > > > > > > Hi Nick, > > > > > > CC Josh > > > > > > On Mon, Oct 26, 2020 at 6:49 PM Nick Desaulniers > > > <ndesaulniers@google.com> wrote: > > > > On Mon, Oct 26, 2020 at 10:44 AM Geert Uytterhoeven > > > > <geert@linux-m68k.org> wrote: > > > > > On Mon, Oct 26, 2020 at 6:39 PM Ard Biesheuvel <ardb@kernel.org> wrote: > > > > > > On Mon, 26 Oct 2020 at 17:01, Geert Uytterhoeven <geert@linux-m68k.org> wrote: > > > > > > > On Mon, Oct 26, 2020 at 2:29 PM Geert Uytterhoeven <geert@linux-m68k.org> wrote: > > > > > > > > On Mon, Oct 26, 2020 at 1:29 PM Geert Uytterhoeven <geert@linux-m68k.org> wrote: > > > > > > > > > I.e. including the ".eh_frame" warning. I have tried bisecting that > > > > > > > > > warning (i.e. with be2881824ae9eb92 reverted), but that leads me to > > > > > > > > > commit b3e5d80d0c48c0cc ("arm64/build: Warn on orphan section > > > > > > > > > placement"), which is another red herring. > > > > > > > > > > > > > > > > kernel/bpf/core.o is the only file containing an eh_frame section, > > > > > > > > causing the warning. > > > > > > > > When I see .eh_frame, I think -fno-asynchronous-unwind-tables is > > > > missing from someone's KBUILD_CFLAGS. > > > > But I don't see anything curious in kernel/bpf/Makefile, unless > > > > cc-disable-warning is somehow broken. > > > > > > I tracked it down to kernel/bpf/core.c:___bpf_prog_run() being tagged > > > with __no_fgcse aka __attribute__((optimize("-fno-gcse"))). > > > > > > Even if the function is trivially empty ("return 0;"), a ".eh_frame" section > > > is generated. Removing the __no_fgcse tag fixes that. > > > > That's weird. I feel pretty strongly that unless we're working around > > a well understood compiler bug with a comment that links to a > > submitted bug report, turning off rando compiler optimizations is a > > terrible hack for which one must proceed straight to jail; do not pass > > go; do not collect $200. But maybe I'd feel differently for this case > > given the context of the change that added it. (Ard mentions > > retpolines+orc+objtool; can someone share the relevant SHA if you have > > it handy so I don't have to go digging?) > > commit 3193c0836f203a91bef96d88c64cccf0be090d9c > Author: Josh Poimboeuf <jpoimboe@redhat.com> > Date: Wed Jul 17 20:36:45 2019 -0500 > > bpf: Disable GCC -fgcse optimization for ___bpf_prog_run() > > has > > Fixes: e55a73251da3 ("bpf: Fix ORC unwinding in non-JIT BPF code") That commit is broken. I had this patch in my queue: -#define __no_fgcse __attribute__((optimize("-fno-gcse"))) +#define __no_fgcse __attribute__((optimize("-fno-gcse,-fno-omit-frame-pointer"))) Sounds like you want to add -fno-asynchronous-unwind-tables to the above list? > and mentions objtool and CONFIG_RETPOLINE. > > > (I feel the same about there > > being an empty asm(); statement in the definition of asm_volatile_goto > > for compiler-gcc.h). Might be time to "fix the compiler." > > > > (It sounds like Arvind is both in agreement with my sentiment, and has > > the root cause). > > > > I agree that the __no_fgcse hack is terrible. Does Clang support the > following pragmas? > > #pragma GCC push_options > #pragma GCC optimize ("-fno-gcse") > #pragma GCC pop_options That will work too, but optimize("-fno...,-fno..,-fno..") is imo cleaner.
diff --git a/arch/arm64/kernel/vmlinux.lds.S b/arch/arm64/kernel/vmlinux.lds.S index 16eb2ef806cd..6ccf19fd2b39 100644 --- a/arch/arm64/kernel/vmlinux.lds.S +++ b/arch/arm64/kernel/vmlinux.lds.S @@ -121,6 +121,14 @@ SECTIONS *(.got) /* Global offset table */ } + /* + * Make sure that the .got.plt is either completely empty or it + * contains only the lazy dispatch entries. + */ + .got.plt : { *(.got.plt) } + ASSERT(SIZEOF(.got.plt) == 0 || SIZEOF(.got.plt) == 0x18, + "Unexpected GOT/PLT entries detected!") + . = ALIGN(SEGMENT_ALIGN); _etext = .; /* End of text section */ @@ -243,6 +251,18 @@ SECTIONS ELF_DETAILS HEAD_SYMBOLS + + /* + * Sections that should stay zero sized, which is safer to + * explicitly check instead of blindly discarding. + */ + .plt : { + *(.plt) *(.plt.*) *(.iplt) *(.igot) + } + ASSERT(SIZEOF(.plt) == 0, "Unexpected run-time procedure linkages detected!") + + .data.rel.ro : { *(.data.rel.ro) } + ASSERT(SIZEOF(.data.rel.ro) == 0, "Unexpected RELRO detected!") } #include "image-vars.h"
In preparation for warning on orphan sections, discard unwanted non-zero-sized generated sections, and enforce other expected-to-be-zero-sized sections (since discarding them might hide problems with them suddenly gaining unexpected entries). Suggested-by: Ard Biesheuvel <ardb@kernel.org> Signed-off-by: Kees Cook <keescook@chromium.org> --- arch/arm64/kernel/vmlinux.lds.S | 20 ++++++++++++++++++++ 1 file changed, 20 insertions(+)