Re: [PATCH 1/2] x86/kprobes: Fix kprobes instruction boudary check with CONFIG_RETHUNK

Peter Zijlstra
2022-09-07T14:29:09Z

On Wed, Sep 07, 2022 at 10:49:13PM +0900, Masami Hiramatsu wrote:
> On Wed, 7 Sep 2022 14:56:52 +0200
> Peter Zijlstra <peterz@infradead.org> wrote:
>
> > On Wed, Sep 07, 2022 at 09:55:21AM +0900, Masami Hiramatsu (Google) wrote:
> >
> > > if (!kallsyms_lookup_size_offset(paddr, NULL, &offset))
> > > return 0;
> > >
> >
> > One more thing:
> >
> > https://lkml.kernel.org/r/20220902130951.853460809@infradead.org
> >
> > can result in negative offsets. The expression:
> >
> > 'paddr - offset'
> >
> > will still get you to +0, but I might not have fully considered things
> > when I wrote that patch.
>
> Hmm, isn't 'offset' unsigned? If 'paddr - offset' is still available
> to find the function entry address, it is OK to me.

Yeah, but the magic of 2s complement means it doesn't matter ;-)