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arch/x86/boot: Use prefix map to avoid embedded paths 

It was observed that the kernel embeds the absolute build path in the
x86 boot image when the __FILE__ macro is expanded.

> From https://bugzilla.yoctoproject.org/show_bug.cgi?id=13458:

  If you turn on the buildpaths QA test, or try a reproducible build, you
  discover that the kernel image contains build paths.

  $ strings bzImage-5.0.19-yocto-standard |grep tmp/
  out of pgt_buf in
  /data/poky-tmp/reproducible/tmp/work-shared/qemux86-64/kernel-source/arch/x86/boot/compressed/kaslr_64.c!?

  But what's this in the top-level Makefile:

  $ git grep prefix-map
  Makefile:KBUILD_CFLAGS  += $(call
  cc-option,-fmacro-prefix-map=$(srctree)/=)

  So the __FILE__ shouldn't be using the full path.  However
  arch/x86/boot/compressed/Makefile has this:

  KBUILD_CFLAGS := -m$(BITS) -O2

  So that clears KBUILD_FLAGS, removing the -fmacro-prefix-map option.

Use -fmacro-prefix-map to have relative paths in the boot image too.

 [ bp: Massage commit message and put the KBUILD_CFLAGS addition in
   ..boot/Makefile after the KBUILD_AFLAGS assignment because gas
   doesn't support -fmacro-prefix-map. ]

Signed-off-by: Bruce Ashfield <bruce.ashfield@gmail.com>
Signed-off-by: Ross Burton <ross.burton@intel.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: George Rimar <grimar@accesssoftek.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Masahiro Yamada <yamada.masahiro@socionext.com>
Cc: Nathan Chancellor <natechancellor@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: x86-ml <x86@kernel.org>
Link: https://lkml.kernel.org/r/20190926093226.8568-1-ross.burton@intel.com
Link: https://bugzilla.kernel.org/show_bug.cgi?id=204333
This commit is contained in:
Bruce Ashfield 2019-09-26 10:32:26 +01:00 committed by Borislav Petkov
parent 54ecb8f702
commit 9e2276fa6e
2 changed files with 2 additions and 0 deletions
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1
arch/x86/boot/Makefile
View File

@ -67,6 +67,7 @@ clean-files += cpustr.h
KBUILD_CFLAGS := $(REALMODE_CFLAGS) -D_SETUP
KBUILD_AFLAGS := $(KBUILD_CFLAGS) -D__ASSEMBLY__
KBUILD_CFLAGS += $(call cc-option,-fmacro-prefix-map=$(srctree)/=)
GCOV_PROFILE := n
UBSAN_SANITIZE := n

1
arch/x86/boot/compressed/Makefile
View File

@ -38,6 +38,7 @@ KBUILD_CFLAGS += $(call cc-option,-fno-stack-protector)
KBUILD_CFLAGS += $(call cc-disable-warning, address-of-packed-member)
KBUILD_CFLAGS += $(call cc-disable-warning, gnu)
KBUILD_CFLAGS += -Wno-pointer-sign
KBUILD_CFLAGS += $(call cc-option,-fmacro-prefix-map=$(srctree)/=)
KBUILD_AFLAGS := $(KBUILD_CFLAGS) -D__ASSEMBLY__
GCOV_PROFILE := n