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

Masami Hiramatsu
2022-09-07T14:15:14Z

On Wed, 7 Sep 2022 15:05:13 +0200
Peter Zijlstra <peterz@infradead.org> wrote:

> On Wed, Sep 07, 2022 at 10:02:41AM +0200, Peter Zijlstra wrote:
>
> > struct queue q;
> >
> > start = paddr - offset;
> > end = start + size;
> > push(&q, paddr - offset);
> >
> > while (start = pop(&q)) {
> > for_each_insn(&insn, start, end, buf) {
> > if (insn.kaddr == paddr)
> > return 1;
> >
> > target = insn_get_branch_addr(&insn);
> > if (target)
> > push(&q, target);
> >
> > if (dead_end_insn(&insn))
> > break;
> > }
> > }
>
> There is the very rare case of intra-function-calls; but I *think*
> they're all in noinstr/nokprobe code anyway.
>
> For instance we have RSB stuffing code like:
>
> .rept 16
> call 1f;
> int3
> 1:
> .endr
> add $(BITS_PER_LONG/8) * 16, %_ASM_SP
>
> And the proposed will be horribly confused by that. But like said; it
> should also never try and untangle it.

Yeah, but I guess if we break the decoding (internal) loop when we
hit an INT3, it maybe possible to be handled?

Thank you,

--
Masami Hiramatsu (Google) <mhiramat@kernel.org>