From: Ard Biesheuvel ard.biesheuvel@linaro.org
[ Upstream commit 3bbd3db86470c701091fb1d67f1fab6621debf50 ]
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.
[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 Signed-off-by: Will Deacon will.deacon@arm.com Signed-off-by: Sasha Levin sashal@kernel.org --- arch/arm64/Makefile | 2 +- arch/arm64/kernel/vmlinux.lds.S | 9 +++++---- 2 files changed, 6 insertions(+), 5 deletions(-)
diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile index 106039d25e2f..35649ee8ad56 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 605d1b60469c..74e469f8a850 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; @@ -176,12 +177,12 @@ 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 = .;