mirror of
https://github.com/torvalds/linux
synced 2024-09-06 18:01:05 +00:00
![Josh Poimboeuf](/assets/img/avatar_default.png)
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
55 lines
1.5 KiB
Makefile
55 lines
1.5 KiB
Makefile
# SPDX-License-Identifier: GPL-2.0-only
|
|
|
|
PHONY := __default
|
|
__default: vmlinux
|
|
|
|
include include/config/auto.conf
|
|
include $(srctree)/scripts/Kbuild.include
|
|
|
|
# for c_flags
|
|
include $(srctree)/scripts/Makefile.lib
|
|
|
|
targets :=
|
|
|
|
quiet_cmd_cc_o_c = CC $@
|
|
cmd_cc_o_c = $(CC) $(c_flags) -c -o $@ $<
|
|
|
|
%.o: %.c FORCE
|
|
$(call if_changed_dep,cc_o_c)
|
|
|
|
ifdef CONFIG_MODULES
|
|
KASAN_SANITIZE_.vmlinux.export.o := n
|
|
KCSAN_SANITIZE_.vmlinux.export.o := n
|
|
GCOV_PROFILE_.vmlinux.export.o := n
|
|
targets += .vmlinux.export.o
|
|
vmlinux: .vmlinux.export.o
|
|
endif
|
|
|
|
ARCH_POSTLINK := $(wildcard $(srctree)/arch/$(SRCARCH)/Makefile.postlink)
|
|
|
|
# Final link of vmlinux with optional arch pass after final link
|
|
cmd_link_vmlinux = \
|
|
$< "$(LD)" "$(KBUILD_LDFLAGS)" "$(LDFLAGS_vmlinux)"; \
|
|
$(if $(ARCH_POSTLINK), $(MAKE) -f $(ARCH_POSTLINK) $@, true)
|
|
|
|
targets += vmlinux
|
|
vmlinux: scripts/link-vmlinux.sh vmlinux.o $(KBUILD_LDS) FORCE
|
|
+$(call if_changed_dep,link_vmlinux)
|
|
|
|
# Add FORCE to the prequisites of a target to force it to be always rebuilt.
|
|
# ---------------------------------------------------------------------------
|
|
|
|
PHONY += FORCE
|
|
FORCE:
|
|
|
|
# Read all saved command lines and dependencies for the $(targets) we
|
|
# may be building above, using $(if_changed{,_dep}). As an
|
|
# optimization, we don't need to read them if the target does not
|
|
# exist, we will rebuild anyway in that case.
|
|
|
|
existing-targets := $(wildcard $(sort $(targets)))
|
|
|
|
-include $(foreach f,$(existing-targets),$(dir $(f)).$(notdir $(f)).cmd)
|
|
|
|
.PHONY: $(PHONY)
|