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SubjectRe: [PATCH v2 34/39] objtool: Validate IBT assumptions
On Mon, Feb 28, 2022 at 10:26:07AM +0100, Peter Zijlstra wrote:
> On Sun, Feb 27, 2022 at 06:00:03PM +0100, Peter Zijlstra wrote:
> > On Sat, Feb 26, 2022 at 07:13:48PM -0800, Josh Poimboeuf wrote:
> > > > +static struct instruction *
> > > > +validate_ibt_reloc(struct objtool_file *file, struct reloc *reloc)
> > > > +{
> > > > + struct instruction *dest;
> > > > + struct section *sec;
> > > > + unsigned long off;
> > > > +
> > > > + sec = reloc->sym->sec;
> > > > + off = reloc->sym->offset + reloc->addend;
> > >
> > > This math assumes non-PC-relative. If it's R_X86_64_PC32 or
> > > R_X86_64_PLT32 then it needs +4 added.
> >
> > Right; so I actually had that PC32 thing in there for a while, but ran
> > into other trouble. I'll go try and figure it out.
>
> Things like .rela.initcall*.init use PC32 but don't need the +4. If we
> get that wrong it'll seal all the initcall and boot doesn't get very
> far at all :-)

Ah...

> How do you feel about something like:
>
> sec = reloc->sym->sec;
> off = reloc->sym->offset;
>
> if ((reloc->sec->base->sh.sh_flags & SHF_EXECINSTR) &&
> (reloc->type == R_X86_64_PC32 || reloc->type == R_X86_64_PLT32))
> off += arch_dest_reloc_offset(reloc->addend);
> else
> off += reloc->addend;
>
>
> hmm ?

Looks good to me.

--
Josh

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