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x86: link vdso and boot with -z noexecstack --no-warn-rwx-segments

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Users of GNU ld (BFD) from binutils 2.39+ will observe multiple
instances of a new warning when linking kernels in the form:

  ld: warning: arch/x86/boot/pmjump.o: missing .note.GNU-stack section implies executable stack
  ld: NOTE: This behaviour is deprecated and will be removed in a future version of the linker
  ld: warning: arch/x86/boot/compressed/vmlinux has a LOAD segment with RWX permissions

Generally, we would like to avoid the stack being executable.  Because
there could be a need for the stack to be executable, assembler sources
have to opt-in to this security feature via explicit creation of the
.note.GNU-stack feature (which compilers create by default) or command
line flag --noexecstack.  Or we can simply tell the linker the
production of such sections is irrelevant and to link the stack as
--noexecstack.

LLVM's LLD linker defaults to -z noexecstack, so this flag isn't
strictly necessary when linking with LLD, only BFD, but it doesn't hurt
to be explicit here for all linkers IMO.  --no-warn-rwx-segments is
currently BFD specific and only available in the current latest release,
so it's wrapped in an ld-option check.

While the kernel makes extensive usage of ELF sections, it doesn't use
permissions from ELF segments.

Link: https://lore.kernel.org/linux-block/3af4127a-f453-4cf7-f133-a181cce06f73@kernel.dk/
Link: https://sourceware.org/git/?p=binutils-gdb.git;a=commit;h=ba951afb99912da01a6e8434126b8fac7aa75107
Link: https://github.com/llvm/llvm-project/issues/57009
Reported-and-tested-by: Jens Axboe <axboe@kernel.dk>
Suggested-by: Fangrui Song <maskray@google.com>
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Nick Desaulniers 2022-08-10 15:24:41 -07:00 committed by Linus Torvalds
parent 0d362be5b1
commit ffcf9c5700
3 changed files with 6 additions and 2 deletions
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2
arch/x86/boot/Makefile
View File

@ -103,7 +103,7 @@ $(obj)/zoffset.h: $(obj)/compressed/vmlinux FORCE
AFLAGS_header.o += -I$(objtree)/$(obj)
$(obj)/header.o: $(obj)/zoffset.h
LDFLAGS_setup.elf := -m elf_i386 -T
LDFLAGS_setup.elf := -m elf_i386 -z noexecstack -T
$(obj)/setup.elf: $(src)/setup.ld $(SETUP_OBJS) FORCE
$(call if_changed,ld)

4
arch/x86/boot/compressed/Makefile
View File

@ -69,6 +69,10 @@ LDFLAGS_vmlinux := -pie $(call ld-option, --no-dynamic-linker)
ifdef CONFIG_LD_ORPHAN_WARN
LDFLAGS_vmlinux += --orphan-handling=warn
endif
LDFLAGS_vmlinux += -z noexecstack
ifeq ($(CONFIG_LD_IS_BFD),y)
LDFLAGS_vmlinux += $(call ld-option,--no-warn-rwx-segments)
endif
LDFLAGS_vmlinux += -T
hostprogs := mkpiggy

2
arch/x86/entry/vdso/Makefile
View File

@ -180,7 +180,7 @@ quiet_cmd_vdso = VDSO $@
sh $(srctree)/$(src)/checkundef.sh '$(NM)' '$@'
VDSO_LDFLAGS = -shared --hash-style=both --build-id=sha1 \
$(call ld-option, --eh-frame-hdr) -Bsymbolic
$(call ld-option, --eh-frame-hdr) -Bsymbolic -z noexecstack
GCOV_PROFILE := n
quiet_cmd_vdso_and_check = VDSO $@