linux-kernel - Re: [RFC][PATCH] x86: Verify access

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Message-ID: <20170120082406.GJ6515@twins.programming.kicks-ass.net>
Date:   Fri, 20 Jan 2017 09:24:06 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Andy Lutomirski <luto@...capital.net>
Cc:     David Smith <dsmith@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Ingo Molnar <mingo@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Frank Ch. Eigler" <fche@...hat.com>
Subject: Re: [RFC][PATCH] x86: Verify access_ok() context

On Wed, Jan 18, 2017 at 04:19:47PM -0800, Andy Lutomirski wrote:
> ISTM even with pagefault_disable() in play, using access_ok() from,
> say, interrupt context is dangerous unless you've first checked that
> you're in a task.  But I guess that in_task() would still return
> false, e.g. in perf.

The test was created exactly because perf was using access_ok()
_wrongly_. See commit: ae31fe51a3cc ("perf/x86: Restore TASK_SIZE check
on frame pointer").