linux/init/Makefile
Josh Poimboeuf 2d7ce49f58 x86/retpoline: Make sure there are no unconverted return thunks due to KCSAN
Enabling CONFIG_KCSAN leads to unconverted, default return thunks to
remain after patching.

As David Kaplan describes in his debugging of the issue, it is caused by
a couple of KCSAN-generated constructors which aren't processed by
objtool:

  "When KCSAN is enabled, GCC generates lots of constructor functions
  named _sub_I_00099_0 which call __tsan_init and then return.  The
  returns in these are generally annotated normally by objtool and fixed
  up at runtime.  But objtool runs on vmlinux.o and vmlinux.o does not
  include a couple of object files that are in vmlinux, like
  init/version-timestamp.o and .vmlinux.export.o, both of which contain
  _sub_I_00099_0 functions.  As a result, the returns in these functions
  are not annotated, and the panic occurs when we call one of them in
  do_ctors and it uses the default return thunk.

  This difference can be seen by counting the number of these functions in the object files:
  $ objdump -d vmlinux.o|grep -c "<_sub_I_00099_0>:"
  2601
  $ objdump -d vmlinux|grep -c "<_sub_I_00099_0>:"
  2603

  If these functions are only run during kernel boot, there is no
  speculation concern."

Fix it by disabling KCSAN on version-timestamp.o and .vmlinux.export.o
so the extra functions don't get generated.  KASAN and GCOV are already
disabled for those files.

  [ bp: Massage commit message. ]

Closes: https://lore.kernel.org/lkml/20231016214810.GA3942238@dev-arch.thelio-3990X/
Reported-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Acked-by: Marco Elver <elver@google.com>
Tested-by: Nathan Chancellor <nathan@kernel.org>
Link: https://lore.kernel.org/r/20231017165946.v4i2d4exyqwqq3bx@treble
2023-10-20 13:02:23 +02:00

65 lines
1.9 KiB
Makefile

# SPDX-License-Identifier: GPL-2.0
#
# Makefile for the linux kernel.
#
ccflags-y := -fno-function-sections -fno-data-sections
obj-y := main.o version.o mounts.o
ifneq ($(CONFIG_BLK_DEV_INITRD),y)
obj-y += noinitramfs.o
else
obj-$(CONFIG_BLK_DEV_INITRD) += initramfs.o
endif
obj-$(CONFIG_GENERIC_CALIBRATE_DELAY) += calibrate.o
obj-y += init_task.o
mounts-y := do_mounts.o
mounts-$(CONFIG_BLK_DEV_RAM) += do_mounts_rd.o
mounts-$(CONFIG_BLK_DEV_INITRD) += do_mounts_initrd.o
#
# UTS_VERSION
#
smp-flag-$(CONFIG_SMP) := SMP
preempt-flag-$(CONFIG_PREEMPT_BUILD) := PREEMPT
preempt-flag-$(CONFIG_PREEMPT_DYNAMIC) := PREEMPT_DYNAMIC
preempt-flag-$(CONFIG_PREEMPT_RT) := PREEMPT_RT
build-version = $(or $(KBUILD_BUILD_VERSION), $(build-version-auto))
build-timestamp = $(or $(KBUILD_BUILD_TIMESTAMP), $(build-timestamp-auto))
# Maximum length of UTS_VERSION is 64 chars
filechk_uts_version = \
utsver=$$(echo '$(pound)'"$(build-version)" $(smp-flag-y) $(preempt-flag-y) "$(build-timestamp)" | cut -b -64); \
echo '$(pound)'define UTS_VERSION \""$${utsver}"\"
#
# Build version.c with temporary UTS_VERSION
#
$(obj)/utsversion-tmp.h: FORCE
$(call filechk,uts_version)
clean-files += utsversion-tmp.h
$(obj)/version.o: $(obj)/utsversion-tmp.h
CFLAGS_version.o := -include $(obj)/utsversion-tmp.h
#
# Build version-timestamp.c with final UTS_VERSION
#
include/generated/utsversion.h: build-version-auto = $(shell $(srctree)/$(src)/build-version)
include/generated/utsversion.h: build-timestamp-auto = $(shell LC_ALL=C date)
include/generated/utsversion.h: FORCE
$(call filechk,uts_version)
$(obj)/version-timestamp.o: include/generated/utsversion.h
CFLAGS_version-timestamp.o := -include include/generated/utsversion.h
KASAN_SANITIZE_version-timestamp.o := n
KCSAN_SANITIZE_version-timestamp.o := n
GCOV_PROFILE_version-timestamp.o := n