Message ID | 20181203195805.28835-1-ard.biesheuvel@linaro.org (mailing list archive) |
---|---|
State | New, archived |
Headers | show |
Series | arm64: relocatable: fix inconsistencies in linker script and options | expand |
Hey Ard, On Mon, Dec 03, 2018 at 08:58:05PM +0100, Ard Biesheuvel wrote: > readelf complains about the section layout of vmlinux when building > with CONFIG_RELOCATABLE=y (for KASLR): > > readelf: Warning: [21]: Link field (0) should index a symtab section. > readelf: Warning: [21]: Info field (0) should index a relocatable section. > > Also, it seems that our use of '-pie -shared' is contradictory, and > thus ambiguous. In general, the way KASLR is wired up at the moment > is highly tailored to how ld.bfd happens to implement (and conflate) > PIE executables and shared libraries, so given the current effort to > support other toolchains, let's fix some of these issues as well. > > - Drop the -pie linker argument and just leave -shared. In ld.bfd, > the differences between them are unclear (except for the ELF type > of the produced image [0]) but lld chokes on seeing both at the > same time. > > - Rename the .rela output section to .rela.dyn, as is customary for > shared libraries and PIE executables, so that it is not misidentified > by readelf as a static relocation section (producing the warnings > above). > > - Pass the -z notext and -z norelro options to explicitly instruct the > linker to permit text relocations, and to omit the RELRO program > header (which requires a certain section layout that we don't adhere > to in the kernel). These are the defaults for current versions of > ld.bfd. > > - Discard .eh_frame and .gnu.hash sections to avoid them from being > emitted between .head.text and .text, screwing up the section layout. > > These changes only affect the ELF image, and produce the same binary > image. Thanks, I've queued this up on for-next/core. > [0] b9dce7f1ba01 ("arm64: kernel: force ET_DYN ELF type for ...") > > Cc: Nick Desaulniers <ndesaulniers@google.com> > Cc: Peter Smith <peter.smith@linaro.org> > Tested-by: Nick Desaulniers <ndesaulniers@google.com> > Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> > --- > This supersedes > > [RFT PATCH] arm64: relocatable: build the kernel as a proper shared library > [RFT PATCH] arm64: add support for building the KASLR kernel with LLVM lld Also, this ^^ is /really/ helpful :) Thanks, Will
diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile index 6cb9fc7e9382..8978f60779c4 100644 --- a/arch/arm64/Makefile +++ b/arch/arm64/Makefile @@ -18,7 +18,7 @@ ifeq ($(CONFIG_RELOCATABLE), y) # Pass --no-apply-dynamic-relocs to restore pre-binutils-2.27 behaviour # for relative relocs, since this leads to better Image compression # with the relocation offsets always being zero. -LDFLAGS_vmlinux += -pie -shared -Bsymbolic \ +LDFLAGS_vmlinux += -shared -Bsymbolic -z notext -z norelro \ $(call ld-option, --no-apply-dynamic-relocs) endif diff --git a/arch/arm64/kernel/vmlinux.lds.S b/arch/arm64/kernel/vmlinux.lds.S index 03b00007553d..7fa008374907 100644 --- a/arch/arm64/kernel/vmlinux.lds.S +++ b/arch/arm64/kernel/vmlinux.lds.S @@ -99,7 +99,8 @@ SECTIONS *(.discard) *(.discard.*) *(.interp .dynamic) - *(.dynsym .dynstr .hash) + *(.dynsym .dynstr .hash .gnu.hash) + *(.eh_frame) } . = KIMAGE_VADDR + TEXT_OFFSET; @@ -192,12 +193,12 @@ SECTIONS PERCPU_SECTION(L1_CACHE_BYTES) - .rela : ALIGN(8) { + .rela.dyn : ALIGN(8) { *(.rela .rela*) } - __rela_offset = ABSOLUTE(ADDR(.rela) - KIMAGE_VADDR); - __rela_size = SIZEOF(.rela); + __rela_offset = ABSOLUTE(ADDR(.rela.dyn) - KIMAGE_VADDR); + __rela_size = SIZEOF(.rela.dyn); . = ALIGN(SEGMENT_ALIGN); __initdata_end = .;