On Mon, Oct 16, 2023 at 10:28:34PM -0700, Josh Poimboeuf wrote: > On Tue, Oct 17, 2023 at 04:31:09AM +0000, Kaplan, David wrote: > > I think I found the problem, although I'm not sure the best way to fix it. > > > > 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. My first thought is that these two object files perhaps should be built without -mfunction-return=thunk-extern. The use of that flag requires objtool to have the intended behavior and objtool isn't seeing these files. > > > > Perhaps another option would be to not compile these two files with KCSAN, as they are already excluded from KASAN and GCOV it looks like. > > I think the latter would be the easy fix, does this make it go away? Tested-by: Nathan Chancellor <nathan@xxxxxxxxxx> Thanks for figuring this out! > 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 > diff --git a/scripts/Makefile.vmlinux b/scripts/Makefile.vmlinux > index 3cd6ca15f390..c9f3e03124d7 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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