linux-kernel - Re: [PATCH] ftrace,kcfi: Separate ftrace_stub() and ftrace_stub

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Message-ID: <202210181121.FEF66CA202@keescook>
Date:   Tue, 18 Oct 2022 11:22:14 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Steven Rostedt <rostedt@...dmis.org>, x86@...nel.org,
        linux-kernel@...r.kernel.org, Mark Rutland <mark.rutland@....com>,
        Sami Tolvanen <samitolvanen@...gle.com>
Subject: Re: [PATCH] ftrace,kcfi: Separate ftrace_stub() and
 ftrace_stub_graph()

On Tue, Oct 18, 2022 at 05:00:33PM +0200, Peter Zijlstra wrote:
> On Tue, Oct 18, 2022 at 07:28:29AM -0700, Kees Cook wrote:
> 
> > Thanks for solving this! Just for future archeology, can you include
> > the splat (I assume you hit a CFI splat) in the commit log, and/or how
> > you triggered the problem? I usually find it helpful in trying to fix
> > similar issues later, etc.
> 
> Unfortunately I didn't save it; it was a while ago (I sorta lost track
> of this fix for a while since it was stuffed in my fineibt queue).
> 
> But Mark ran it today to confirm on arm64 and there it looks like
> (harvested from IRC):
> 
>   [    3.153082] CFI failure at ftrace_return_to_handler+0xac/0x16c (target: ftrace_stub+0x0/0x14; expected type: 0x0a5d5347)
> 
> I think simply enabling the ftrace boot time tests is enough to trigger
> this.

Ah-ha, perfect. Thanks! (If it's not yet in tip, can you update the
commit log?)

-- 
Kees Cook