Messages in this thread | | | Date | Thu, 8 Sep 2022 00:22:27 +0900 | From | Masami Hiramatsu (Google) <> | Subject | Re: [PATCH 1/2] x86/kprobes: Fix kprobes instruction boudary check with CONFIG_RETHUNK |
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On Wed, 7 Sep 2022 16:27:59 +0200 Peter Zijlstra <peterz@infradead.org> wrote:
> On Wed, Sep 07, 2022 at 11:14:50PM +0900, Masami Hiramatsu wrote: > > 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? > > If you make insn_get_branch_addr() return the target of CALL > instructions when this target is between function start and end, it > should work I think.
Ah Indeed. Anyway, I would like to use INT3 as a stop instruction, instread of checking dead_end_instruction. Is there any problem?
> > But like said; this construct is rare and all instances I can remember > should not be kprobes to begin with. These are all 'fun' things like > retpoline stubs and the the above RSB stuff loop.
Agree. That should not appear on normal code.
Thank you,
-- Masami Hiramatsu (Google) <mhiramat@kernel.org>
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