linux-kernel - Re: [PATCH 2/3] perf, x86: Don't leak kernel data via callchains

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Message-ID: <CA+55aFwE=-52Ld=KW6QKmSSfUnSd5Jw90xEouvNHT_kSFm3FFQ@mail.gmail.com>
Date:	Fri, 20 Apr 2012 12:57:00 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Arun Sharma <asharma@...com>
Cc:	linux-kernel@...r.kernel.org,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: [PATCH 2/3] perf, x86: Don't leak kernel data via callchains

On Fri, Apr 20, 2012 at 12:35 PM, Arun Sharma <asharma@...com> wrote:
>
> +       set_fs(USER_DS);

NAK.

I really don't think this is the right thing to do. We're in random
NMI context, set_fs() is not at all necessarily safe.

No, the code needs to check the frame range by hand, not depend on current-fs.

In fact, I'd argue that this is a bug in copy_from_user_nmi(), which
should simply check the *user* address space explicitly, not using
access_ok().

                   Linus
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