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linux-next/init/Makefile
Sami Tolvanen 42633ed852 kbuild: Fix CFI hash randomization with KASAN
Clang emits a asan.module_ctor constructor to each object file
when KASAN is enabled, and these functions are indirectly called
in do_ctors. With CONFIG_CFI_CLANG, the compiler also emits a CFI
type hash before each address-taken global function so they can
pass indirect call checks.

However, in commit 0c3e806ec0 ("x86/cfi: Add boot time hash
randomization"), x86 implemented boot time hash randomization,
which relies on the .cfi_sites section generated by objtool. As
objtool is run against vmlinux.o instead of individual object
files with X86_KERNEL_IBT (enabled by default), CFI types in
object files that are not part of vmlinux.o end up not being
included in .cfi_sites, and thus won't get randomized and trip
CFI when called.

Only .vmlinux.export.o and init/version-timestamp.o are linked
into vmlinux separately from vmlinux.o. As these files don't
contain any functions, disable KASAN for both of them to avoid
breaking hash randomization.

Link: https://github.com/ClangBuiltLinux/linux/issues/1742
Fixes: 0c3e806ec0 ("x86/cfi: Add boot time hash randomization")
Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20230112224948.1479453-2-samitolvanen@google.com
2023-01-13 15:22:03 -08:00

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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