| Message ID | 201908131602.6E858DEC@keescook (mailing list archive) |
|---|---|
| State | Mainlined |
| Commit | 90776dd1c427cbb4d381aa4b13338f1fb1d20f5e |
| Headers | show |
| Series | arm64/efi: Move variable assignments after SECTIONS | expand |
On Wed, 14 Aug 2019 at 02:04, Kees Cook <keescook@chromium.org> wrote: > > It seems that LLVM's linker does not correctly handle variable assignments > involving section positions that are updated during the SECTIONS > parsing. Commit aa69fb62bea1 ("arm64/efi: Mark __efistub_stext_offset as > an absolute symbol explicitly") ran into this too, but found a different > workaround. > > However, this was not enough, as other variables were also miscalculated > which manifested as boot failures under UEFI where __efistub__end was > not taking the correct _end value (they should be the same): > > $ ld.lld -EL -maarch64elf --no-undefined -X -shared \ > -Bsymbolic -z notext -z norelro --no-apply-dynamic-relocs \ > -o vmlinux.lld -T poc.lds --whole-archive vmlinux.o && \ > readelf -Ws vmlinux.lld | egrep '\b(__efistub_|)_end\b' > 368272: ffff000002218000 0 NOTYPE LOCAL HIDDEN 38 __efistub__end > 368322: ffff000012318000 0 NOTYPE GLOBAL DEFAULT 38 _end > > $ aarch64-linux-gnu-ld.bfd -EL -maarch64elf --no-undefined -X -shared \ > -Bsymbolic -z notext -z norelro --no-apply-dynamic-relocs \ > -o vmlinux.bfd -T poc.lds --whole-archive vmlinux.o && \ > readelf -Ws vmlinux.bfd | egrep '\b(__efistub_|)_end\b' > 338124: ffff000012318000 0 NOTYPE LOCAL DEFAULT ABS __efistub__end > 383812: ffff000012318000 0 NOTYPE GLOBAL DEFAULT 15325 _end > > To work around this, all of the __efistub_-prefixed variable assignments > need to be moved after the linker script's SECTIONS entry. As it turns > out, this also solves the problem fixed in commit aa69fb62bea1, so those > changes are reverted here. > > Link: https://github.com/ClangBuiltLinux/linux/issues/634 > Link: https://bugs.llvm.org/show_bug.cgi?id=42990 > Signed-off-by: Kees Cook <keescook@chromium.org> Although it is slightly disappointing that we need to work around this kind of bugs when adding support for a new toolchain, I don't see anything wrong with this patch, so Acked-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> > --- > arch/arm64/kernel/image-vars.h | 51 +++++++++++++++++++++++++++++++++ > arch/arm64/kernel/image.h | 42 --------------------------- > arch/arm64/kernel/vmlinux.lds.S | 2 ++ > 3 files changed, 53 insertions(+), 42 deletions(-) > create mode 100644 arch/arm64/kernel/image-vars.h > > diff --git a/arch/arm64/kernel/image-vars.h b/arch/arm64/kernel/image-vars.h > new file mode 100644 > index 000000000000..25a2a9b479c2 > --- /dev/null > +++ b/arch/arm64/kernel/image-vars.h > @@ -0,0 +1,51 @@ > +/* SPDX-License-Identifier: GPL-2.0-only */ > +/* > + * Linker script variables to be set after section resolution, as > + * ld.lld does not like variables assigned before SECTIONS is processed. > + */ > +#ifndef __ARM64_KERNEL_IMAGE_VARS_H > +#define __ARM64_KERNEL_IMAGE_VARS_H > + > +#ifndef LINKER_SCRIPT > +#error This file should only be included in vmlinux.lds.S > +#endif > + > +#ifdef CONFIG_EFI > + > +__efistub_stext_offset = stext - _text; > + > +/* > + * The EFI stub has its own symbol namespace prefixed by __efistub_, to > + * isolate it from the kernel proper. The following symbols are legally > + * accessed by the stub, so provide some aliases to make them accessible. > + * Only include data symbols here, or text symbols of functions that are > + * guaranteed to be safe when executed at another offset than they were > + * linked at. The routines below are all implemented in assembler in a > + * position independent manner > + */ > +__efistub_memcmp = __pi_memcmp; > +__efistub_memchr = __pi_memchr; > +__efistub_memcpy = __pi_memcpy; > +__efistub_memmove = __pi_memmove; > +__efistub_memset = __pi_memset; > +__efistub_strlen = __pi_strlen; > +__efistub_strnlen = __pi_strnlen; > +__efistub_strcmp = __pi_strcmp; > +__efistub_strncmp = __pi_strncmp; > +__efistub_strrchr = __pi_strrchr; > +__efistub___flush_dcache_area = __pi___flush_dcache_area; > + > +#ifdef CONFIG_KASAN > +__efistub___memcpy = __pi_memcpy; > +__efistub___memmove = __pi_memmove; > +__efistub___memset = __pi_memset; > +#endif > + > +__efistub__text = _text; > +__efistub__end = _end; > +__efistub__edata = _edata; > +__efistub_screen_info = screen_info; > + > +#endif > + > +#endif /* __ARM64_KERNEL_IMAGE_VARS_H */ > diff --git a/arch/arm64/kernel/image.h b/arch/arm64/kernel/image.h > index 2b85c0d6fa3d..c7d38c660372 100644 > --- a/arch/arm64/kernel/image.h > +++ b/arch/arm64/kernel/image.h > @@ -65,46 +65,4 @@ > DEFINE_IMAGE_LE64(_kernel_offset_le, TEXT_OFFSET); \ > DEFINE_IMAGE_LE64(_kernel_flags_le, __HEAD_FLAGS); > > -#ifdef CONFIG_EFI > - > -/* > - * Use ABSOLUTE() to avoid ld.lld treating this as a relative symbol: > - * https://github.com/ClangBuiltLinux/linux/issues/561 > - */ > -__efistub_stext_offset = ABSOLUTE(stext - _text); > - > -/* > - * The EFI stub has its own symbol namespace prefixed by __efistub_, to > - * isolate it from the kernel proper. The following symbols are legally > - * accessed by the stub, so provide some aliases to make them accessible. > - * Only include data symbols here, or text symbols of functions that are > - * guaranteed to be safe when executed at another offset than they were > - * linked at. The routines below are all implemented in assembler in a > - * position independent manner > - */ > -__efistub_memcmp = __pi_memcmp; > -__efistub_memchr = __pi_memchr; > -__efistub_memcpy = __pi_memcpy; > -__efistub_memmove = __pi_memmove; > -__efistub_memset = __pi_memset; > -__efistub_strlen = __pi_strlen; > -__efistub_strnlen = __pi_strnlen; > -__efistub_strcmp = __pi_strcmp; > -__efistub_strncmp = __pi_strncmp; > -__efistub_strrchr = __pi_strrchr; > -__efistub___flush_dcache_area = __pi___flush_dcache_area; > - > -#ifdef CONFIG_KASAN > -__efistub___memcpy = __pi_memcpy; > -__efistub___memmove = __pi_memmove; > -__efistub___memset = __pi_memset; > -#endif > - > -__efistub__text = _text; > -__efistub__end = _end; > -__efistub__edata = _edata; > -__efistub_screen_info = screen_info; > - > -#endif > - > #endif /* __ARM64_KERNEL_IMAGE_H */ > diff --git a/arch/arm64/kernel/vmlinux.lds.S b/arch/arm64/kernel/vmlinux.lds.S > index 7fa008374907..803b24d2464a 100644 > --- a/arch/arm64/kernel/vmlinux.lds.S > +++ b/arch/arm64/kernel/vmlinux.lds.S > @@ -245,6 +245,8 @@ SECTIONS > HEAD_SYMBOLS > } > > +#include "image-vars.h" > + > /* > * The HYP init code and ID map text can't be longer than a page each, > * and should not cross a page boundary. > -- > 2.17.1 > > > -- > Kees Cook
On Wed, Aug 14, 2019 at 07:14:42PM +0300, Ard Biesheuvel wrote: > On Wed, 14 Aug 2019 at 02:04, Kees Cook <keescook@chromium.org> wrote: > > > > It seems that LLVM's linker does not correctly handle variable assignments > > involving section positions that are updated during the SECTIONS > > parsing. Commit aa69fb62bea1 ("arm64/efi: Mark __efistub_stext_offset as > > an absolute symbol explicitly") ran into this too, but found a different > > workaround. > > > > However, this was not enough, as other variables were also miscalculated > > which manifested as boot failures under UEFI where __efistub__end was > > not taking the correct _end value (they should be the same): > > > > $ ld.lld -EL -maarch64elf --no-undefined -X -shared \ > > -Bsymbolic -z notext -z norelro --no-apply-dynamic-relocs \ > > -o vmlinux.lld -T poc.lds --whole-archive vmlinux.o && \ > > readelf -Ws vmlinux.lld | egrep '\b(__efistub_|)_end\b' > > 368272: ffff000002218000 0 NOTYPE LOCAL HIDDEN 38 __efistub__end > > 368322: ffff000012318000 0 NOTYPE GLOBAL DEFAULT 38 _end > > > > $ aarch64-linux-gnu-ld.bfd -EL -maarch64elf --no-undefined -X -shared \ > > -Bsymbolic -z notext -z norelro --no-apply-dynamic-relocs \ > > -o vmlinux.bfd -T poc.lds --whole-archive vmlinux.o && \ > > readelf -Ws vmlinux.bfd | egrep '\b(__efistub_|)_end\b' > > 338124: ffff000012318000 0 NOTYPE LOCAL DEFAULT ABS __efistub__end > > 383812: ffff000012318000 0 NOTYPE GLOBAL DEFAULT 15325 _end > > > > To work around this, all of the __efistub_-prefixed variable assignments > > need to be moved after the linker script's SECTIONS entry. As it turns > > out, this also solves the problem fixed in commit aa69fb62bea1, so those > > changes are reverted here. > > > > Link: https://github.com/ClangBuiltLinux/linux/issues/634 > > Link: https://bugs.llvm.org/show_bug.cgi?id=42990 > > Signed-off-by: Kees Cook <keescook@chromium.org> > > Although it is slightly disappointing that we need to work around this > kind of bugs when adding support for a new toolchain, I don't see > anything wrong with this patch, so > > Acked-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> Yup, it's gross, but I'll queue it with your ack. Will
On Wed, Aug 14, 2019 at 05:19:04PM +0100, Will Deacon wrote: > On Wed, Aug 14, 2019 at 07:14:42PM +0300, Ard Biesheuvel wrote: > > On Wed, 14 Aug 2019 at 02:04, Kees Cook <keescook@chromium.org> wrote: > > > > > > It seems that LLVM's linker does not correctly handle variable assignments > > > involving section positions that are updated during the SECTIONS > > > parsing. Commit aa69fb62bea1 ("arm64/efi: Mark __efistub_stext_offset as > > > an absolute symbol explicitly") ran into this too, but found a different > > > workaround. > > > > > > However, this was not enough, as other variables were also miscalculated > > > which manifested as boot failures under UEFI where __efistub__end was > > > not taking the correct _end value (they should be the same): > > > > > > $ ld.lld -EL -maarch64elf --no-undefined -X -shared \ > > > -Bsymbolic -z notext -z norelro --no-apply-dynamic-relocs \ > > > -o vmlinux.lld -T poc.lds --whole-archive vmlinux.o && \ > > > readelf -Ws vmlinux.lld | egrep '\b(__efistub_|)_end\b' > > > 368272: ffff000002218000 0 NOTYPE LOCAL HIDDEN 38 __efistub__end > > > 368322: ffff000012318000 0 NOTYPE GLOBAL DEFAULT 38 _end > > > > > > $ aarch64-linux-gnu-ld.bfd -EL -maarch64elf --no-undefined -X -shared \ > > > -Bsymbolic -z notext -z norelro --no-apply-dynamic-relocs \ > > > -o vmlinux.bfd -T poc.lds --whole-archive vmlinux.o && \ > > > readelf -Ws vmlinux.bfd | egrep '\b(__efistub_|)_end\b' > > > 338124: ffff000012318000 0 NOTYPE LOCAL DEFAULT ABS __efistub__end > > > 383812: ffff000012318000 0 NOTYPE GLOBAL DEFAULT 15325 _end > > > > > > To work around this, all of the __efistub_-prefixed variable assignments > > > need to be moved after the linker script's SECTIONS entry. As it turns > > > out, this also solves the problem fixed in commit aa69fb62bea1, so those > > > changes are reverted here. > > > > > > Link: https://github.com/ClangBuiltLinux/linux/issues/634 > > > Link: https://bugs.llvm.org/show_bug.cgi?id=42990 > > > Signed-off-by: Kees Cook <keescook@chromium.org> > > > > Although it is slightly disappointing that we need to work around this > > kind of bugs when adding support for a new toolchain, I don't see > > anything wrong with this patch, so > > > > Acked-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> > > Yup, it's gross, but I'll queue it with your ack. Thanks, and agreed. :)
diff --git a/arch/arm64/kernel/image-vars.h b/arch/arm64/kernel/image-vars.h new file mode 100644 index 000000000000..25a2a9b479c2 --- /dev/null +++ b/arch/arm64/kernel/image-vars.h @@ -0,0 +1,51 @@ +/* SPDX-License-Identifier: GPL-2.0-only */ +/* + * Linker script variables to be set after section resolution, as + * ld.lld does not like variables assigned before SECTIONS is processed. + */ +#ifndef __ARM64_KERNEL_IMAGE_VARS_H +#define __ARM64_KERNEL_IMAGE_VARS_H + +#ifndef LINKER_SCRIPT +#error This file should only be included in vmlinux.lds.S +#endif + +#ifdef CONFIG_EFI + +__efistub_stext_offset = stext - _text; + +/* + * The EFI stub has its own symbol namespace prefixed by __efistub_, to + * isolate it from the kernel proper. The following symbols are legally + * accessed by the stub, so provide some aliases to make them accessible. + * Only include data symbols here, or text symbols of functions that are + * guaranteed to be safe when executed at another offset than they were + * linked at. The routines below are all implemented in assembler in a + * position independent manner + */ +__efistub_memcmp = __pi_memcmp; +__efistub_memchr = __pi_memchr; +__efistub_memcpy = __pi_memcpy; +__efistub_memmove = __pi_memmove; +__efistub_memset = __pi_memset; +__efistub_strlen = __pi_strlen; +__efistub_strnlen = __pi_strnlen; +__efistub_strcmp = __pi_strcmp; +__efistub_strncmp = __pi_strncmp; +__efistub_strrchr = __pi_strrchr; +__efistub___flush_dcache_area = __pi___flush_dcache_area; + +#ifdef CONFIG_KASAN +__efistub___memcpy = __pi_memcpy; +__efistub___memmove = __pi_memmove; +__efistub___memset = __pi_memset; +#endif + +__efistub__text = _text; +__efistub__end = _end; +__efistub__edata = _edata; +__efistub_screen_info = screen_info; + +#endif + +#endif /* __ARM64_KERNEL_IMAGE_VARS_H */ diff --git a/arch/arm64/kernel/image.h b/arch/arm64/kernel/image.h index 2b85c0d6fa3d..c7d38c660372 100644 --- a/arch/arm64/kernel/image.h +++ b/arch/arm64/kernel/image.h @@ -65,46 +65,4 @@ DEFINE_IMAGE_LE64(_kernel_offset_le, TEXT_OFFSET); \ DEFINE_IMAGE_LE64(_kernel_flags_le, __HEAD_FLAGS); -#ifdef CONFIG_EFI - -/* - * Use ABSOLUTE() to avoid ld.lld treating this as a relative symbol: - * https://github.com/ClangBuiltLinux/linux/issues/561 - */ -__efistub_stext_offset = ABSOLUTE(stext - _text); - -/* - * The EFI stub has its own symbol namespace prefixed by __efistub_, to - * isolate it from the kernel proper. The following symbols are legally - * accessed by the stub, so provide some aliases to make them accessible. - * Only include data symbols here, or text symbols of functions that are - * guaranteed to be safe when executed at another offset than they were - * linked at. The routines below are all implemented in assembler in a - * position independent manner - */ -__efistub_memcmp = __pi_memcmp; -__efistub_memchr = __pi_memchr; -__efistub_memcpy = __pi_memcpy; -__efistub_memmove = __pi_memmove; -__efistub_memset = __pi_memset; -__efistub_strlen = __pi_strlen; -__efistub_strnlen = __pi_strnlen; -__efistub_strcmp = __pi_strcmp; -__efistub_strncmp = __pi_strncmp; -__efistub_strrchr = __pi_strrchr; -__efistub___flush_dcache_area = __pi___flush_dcache_area; - -#ifdef CONFIG_KASAN -__efistub___memcpy = __pi_memcpy; -__efistub___memmove = __pi_memmove; -__efistub___memset = __pi_memset; -#endif - -__efistub__text = _text; -__efistub__end = _end; -__efistub__edata = _edata; -__efistub_screen_info = screen_info; - -#endif - #endif /* __ARM64_KERNEL_IMAGE_H */ diff --git a/arch/arm64/kernel/vmlinux.lds.S b/arch/arm64/kernel/vmlinux.lds.S index 7fa008374907..803b24d2464a 100644 --- a/arch/arm64/kernel/vmlinux.lds.S +++ b/arch/arm64/kernel/vmlinux.lds.S @@ -245,6 +245,8 @@ SECTIONS HEAD_SYMBOLS } +#include "image-vars.h" + /* * The HYP init code and ID map text can't be longer than a page each, * and should not cross a page boundary.
It seems that LLVM's linker does not correctly handle variable assignments involving section positions that are updated during the SECTIONS parsing. Commit aa69fb62bea1 ("arm64/efi: Mark __efistub_stext_offset as an absolute symbol explicitly") ran into this too, but found a different workaround. However, this was not enough, as other variables were also miscalculated which manifested as boot failures under UEFI where __efistub__end was not taking the correct _end value (they should be the same): $ ld.lld -EL -maarch64elf --no-undefined -X -shared \ -Bsymbolic -z notext -z norelro --no-apply-dynamic-relocs \ -o vmlinux.lld -T poc.lds --whole-archive vmlinux.o && \ readelf -Ws vmlinux.lld | egrep '\b(__efistub_|)_end\b' 368272: ffff000002218000 0 NOTYPE LOCAL HIDDEN 38 __efistub__end 368322: ffff000012318000 0 NOTYPE GLOBAL DEFAULT 38 _end $ aarch64-linux-gnu-ld.bfd -EL -maarch64elf --no-undefined -X -shared \ -Bsymbolic -z notext -z norelro --no-apply-dynamic-relocs \ -o vmlinux.bfd -T poc.lds --whole-archive vmlinux.o && \ readelf -Ws vmlinux.bfd | egrep '\b(__efistub_|)_end\b' 338124: ffff000012318000 0 NOTYPE LOCAL DEFAULT ABS __efistub__end 383812: ffff000012318000 0 NOTYPE GLOBAL DEFAULT 15325 _end To work around this, all of the __efistub_-prefixed variable assignments need to be moved after the linker script's SECTIONS entry. As it turns out, this also solves the problem fixed in commit aa69fb62bea1, so those changes are reverted here. Link: https://github.com/ClangBuiltLinux/linux/issues/634 Link: https://bugs.llvm.org/show_bug.cgi?id=42990 Signed-off-by: Kees Cook <keescook@chromium.org> --- arch/arm64/kernel/image-vars.h | 51 +++++++++++++++++++++++++++++++++ arch/arm64/kernel/image.h | 42 --------------------------- arch/arm64/kernel/vmlinux.lds.S | 2 ++ 3 files changed, 53 insertions(+), 42 deletions(-) create mode 100644 arch/arm64/kernel/image-vars.h