The following commit has been merged into the x86/bugs branch of tip: Commit-ID: 2d7ce49f58dc95495b3e22e45d2be7de909b2c63 Gitweb: https://git.kernel.org/tip/2d7ce49f58dc95495b3e22e45d2be7de909b2c63 Author: Josh Poimboeuf <jpoimboe@xxxxxxxxxx> AuthorDate: Tue, 17 Oct 2023 09:59:46 -07:00 Committer: Borislav Petkov (AMD) <bp@xxxxxxxxx> CommitterDate: Fri, 20 Oct 2023 13:02:23 +02:00 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@xxxxxxxxxx> Signed-off-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx> Signed-off-by: Borislav Petkov (AMD) <bp@xxxxxxxxx> Reviewed-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx> Acked-by: Marco Elver <elver@xxxxxxxxxx> Tested-by: Nathan Chancellor <nathan@xxxxxxxxxx> Link: https://lore.kernel.org/r/20231017165946.v4i2d4exyqwqq3bx@treble --- init/Makefile | 1 + scripts/Makefile.vmlinux | 1 + 2 files changed, 2 insertions(+) diff --git a/init/Makefile b/init/Makefile index ec557ad..cbac576 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 3cd6ca1..c9f3e03 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
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