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Josh Poimboeuf authored
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:
2d7ce49f
