[AMD Official Use Only - General] > -----Original Message----- > From: Josh Poimboeuf <jpoimboe@xxxxxxxxxx> > Sent: Tuesday, October 17, 2023 12:29 AM > To: Kaplan, David <David.Kaplan@xxxxxxx> > Cc: Nathan Chancellor <nathan@xxxxxxxxxx>; Borislav Petkov > <bp@xxxxxxxxx>; linux-kernel@xxxxxxxxxxxxxxx; linux-tip- > commits@xxxxxxxxxxxxxxx; Ingo Molnar <mingo@xxxxxxxxxx>; Peter Zijlstra > (Intel) <peterz@xxxxxxxxxxxxx>; x86@xxxxxxxxxx; llvm@xxxxxxxxxxxxxxx > Subject: Re: [tip: x86/bugs] x86/retpoline: Ensure default return thunk isn't > used at runtime > > Caution: This message originated from an External Source. Use proper > caution when opening attachments, clicking links, or responding. > > > 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? > > 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 Yes, that worked for me. With this the VM booted and the number of these sub_I_00099_0 functions was consistent between vmlinux.o and vmlinux. --David Kaplan
|