linux-kernel - Re: [PATCH 1/2] x86/kprobes: Fix kprobes instruction boudary check with CONFIG

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Message-Id: <20220907231450.0a5f085319251349a45465d8@kernel.org>
Date:   Wed, 7 Sep 2022 23:14:50 +0900
From:   Masami Hiramatsu (Google) <mhiramat@...nel.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...nel.org>,
        Suleiman Souhlal <suleiman@...gle.com>,
        bpf <bpf@...r.kernel.org>, linux-kernel@...r.kernel.org,
        Borislav Petkov <bp@...e.de>,
        Josh Poimboeuf <jpoimboe@...nel.org>, x86@...nel.org
Subject: Re: [PATCH 1/2] x86/kprobes: Fix kprobes instruction boudary check
 with CONFIG_RETHUNK

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