linux-kernel - Re: [PATCH -tip v4 10/12] x86/kprobes: Push a fake return address at kretprobe

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Date:   Wed, 24 Mar 2021 11:01:43 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Masami Hiramatsu <mhiramat@...nel.org>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...nel.org>, X86 ML <x86@...nel.org>,
        Daniel Xu <dxu@...uu.xyz>, linux-kernel@...r.kernel.org,
        bpf@...r.kernel.org, kuba@...nel.org, mingo@...hat.com,
        ast@...nel.org, tglx@...utronix.de, kernel-team@...com, yhs@...com,
        linux-ia64@...r.kernel.org,
        Abhishek Sagar <sagar.abhishek@...il.com>
Subject: Re: [PATCH -tip v4 10/12] x86/kprobes: Push a fake return address at
 kretprobe_trampoline

On Wed, Mar 24, 2021 at 10:40:58AM +0900, Masami Hiramatsu wrote:
> On Tue, 23 Mar 2021 23:30:07 +0100
> Peter Zijlstra <peterz@...radead.org> wrote:
> 
> > On Mon, Mar 22, 2021 at 03:41:40PM +0900, Masami Hiramatsu wrote:
> > >  	".global kretprobe_trampoline\n"
> > >  	".type kretprobe_trampoline, @function\n"
> > >  	"kretprobe_trampoline:\n"
> > >  #ifdef CONFIG_X86_64
> > 
> > So what happens if we get an NMI here? That is, after the RET but before
> > the push? Then our IP points into the trampoline but we've not done that
> > push yet.
> 
> Not only NMI, but also interrupts can happen. There is no cli/sti here.
> 
> Anyway, thanks for pointing!
> I think in UNWIND_HINT_TYPE_REGS and UNWIND_HINT_TYPE_REGS_PARTIAL cases
> ORC unwinder also has to check the state->ip and if it is kretprobe_trampoline,
> it should be recovered.
> What about this?

I think the REGS and REGS_PARTIAL cases can also be affected by function
graph tracing.  So should they use the generic unwind_recover_ret_addr()
instead of unwind_recover_kretprobe()?

-- 
Josh