From: Josh Poimboeuf jpoimboe@kernel.org
[ Upstream commit 2d7ce49f58dc95495b3e22e45d2be7de909b2c63 ]
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 Signed-off-by: Sasha Levin sashal@kernel.org --- init/Makefile | 1 + scripts/Makefile.vmlinux | 1 + 2 files changed, 2 insertions(+)
diff --git a/init/Makefile b/init/Makefile index ec557ada3c12e..cbac576c57d63 100644 --- a/init/Makefile +++ b/init/Makefile @@ -60,4 +60,5 @@ include/generated/utsversion.h: FORCE $(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 diff --git a/scripts/Makefile.vmlinux b/scripts/Makefile.vmlinux index 3cd6ca15f390d..c9f3e03124d7f 100644 --- a/scripts/Makefile.vmlinux +++ b/scripts/Makefile.vmlinux @@ -19,6 +19,7 @@ quiet_cmd_cc_o_c = CC $@
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