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

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Date:   Tue, 18 Oct 2022 17:00:33 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Kees Cook <kees.cook@...ux.dev>
Cc:     Steven Rostedt <rostedt@...dmis.org>, x86@...nel.org,
        linux-kernel@...r.kernel.org, Mark Rutland <mark.rutland@....com>,
        Kees Cook <keescook@...omium.org>,
        Sami Tolvanen <samitolvanen@...gle.com>
Subject: Re: [PATCH] ftrace,kcfi: Separate ftrace_stub() and
 ftrace_stub_graph()

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.