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| author | Josh Poimboeuf <jpoimboe@kernel.org> | 2023-10-17 09:59:46 -0700 |
|---|---|---|
| committer | Borislav Petkov (AMD) <bp@alien8.de> | 2023-10-20 13:02:23 +0200 |
| commit | 2d7ce49f58dc95495b3e22e45d2be7de909b2c63 (patch) | |
| tree | 566e79f697f788330bf2de7748ff6dba7756d61f /init | |
| parent | 321a145137653188b8bf9a6b6fc60e8ccb184392 (diff) | |
| download | lwn-2d7ce49f58dc95495b3e22e45d2be7de909b2c63.tar.gz lwn-2d7ce49f58dc95495b3e22e45d2be7de909b2c63.zip | |
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
Diffstat (limited to 'init')
| -rw-r--r-- | init/Makefile | 1 |
1 files changed, 1 insertions, 0 deletions
diff --git a/init/Makefile b/init/Makefile index ec557ada3c12..cbac576c57d6 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 |