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Date: Fri, 20 Jan 2017 09:24:06 +0100
From: Peter Zijlstra <peterz@infradead.org>
To: Andy Lutomirski <luto@amacapital.net>
Cc: David Smith <dsmith@redhat.com>, Thomas Gleixner <tglx@linutronix.de>,
        Linus Torvalds <torvalds@linux-foundation.org>,
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        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "Frank Ch. Eigler" <fche@redhat.com>
Subject: Re: [RFC][PATCH] x86: Verify access_ok() context
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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").