Re: [PATCH v4 00/21] KCFI support

[Sami Tolvanen]

On Fri, Sep 2, 2022 at 12:51 AM Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
>
> On Thu, Sep 01, 2022 at 05:33:29PM -0700, Sami Tolvanen wrote:
>
> > > I do see a few new objtool warnings as well:
> > >
> > > vmlinux.o: warning: objtool: apply_relocate_add+0x34: relocation to !ENDBR: memcpy+0x0
> > > vmlinux.o: warning: objtool: ___ksymtab+__memcpy+0x0: data relocation to !ENDBR: memcpy+0x0
> > > vmlinux.o: warning: objtool: ___ksymtab+memcpy+0x0: data relocation to !ENDBR: memcpy+0x0
> >
> > That's interesting. I can only reproduce this warning with
> > allmodconfig+LTO, even though the relocation exists in all builds (the
> > code makes an indirect call to memcpy) and memcpy (aliased to
> > __memcpy) doesn't start with endbr. I'll have to take a closer look at
> > why this warning only appears with LTO.
>
> From just looking at the patches I'd say patch #19 breaks it. IIRC you
> forgot to make the SYM_TYPED_FUNC things emit ENDBR.
>
> Look at how x86/asm/linkage.h is overriding SYM_FUNC_START*().

Yes, that's the reason, I'll fix this next week. I was mostly
wondering why I'm not getting this warning with my other test configs,
but it looks like IBT isn't enabled by default.

Sami