From mboxrd@z Thu Jan  1 00:00:00 1970
From: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Subject: Re: [PATCH 1/1] drm/i915: shorten i915_next_seqno
	debugfs output
Date: Fri, 12 Apr 2013 12:15:54 +0300
Message-ID: <878v4oxg6t.fsf@gaia.fi.intel.com>
References: <1365686532-6682-1-git-send-email-mika.kuoppala@intel.com>
	<CAGXu5j+G2VLnDVxR2Qf7ctN4A69mcr43c-pZmnE4PUQc7j3CrQ@mail.gmail.com>
	<87bo9lxcuc.fsf@gaia.fi.intel.com>
	<CAGXu5jLUkYwcDdvXe+-24CQPxGDOZm_SjT_4ab7Z0YZRVfqPPQ@mail.gmail.com>
Mime-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: 7bit
Return-path: <intel-gfx-bounces+gcfxdi-intel-gfx=m.gmane.org@lists.freedesktop.org>
Received: from mga14.intel.com (mga14.intel.com [143.182.124.37])
	by gabe.freedesktop.org (Postfix) with ESMTP id 00DC1E5C33
	for <intel-gfx@lists.freedesktop.org>;
	Fri, 12 Apr 2013 02:16:22 -0700 (PDT)
In-Reply-To: <CAGXu5jLUkYwcDdvXe+-24CQPxGDOZm_SjT_4ab7Z0YZRVfqPPQ@mail.gmail.com>
List-Unsubscribe: <http://lists.freedesktop.org/mailman/options/intel-gfx>,
	<mailto:intel-gfx-request@lists.freedesktop.org?subject=unsubscribe>
List-Archive: <http://lists.freedesktop.org/archives/intel-gfx>
List-Post: <mailto:intel-gfx@lists.freedesktop.org>
List-Help: <mailto:intel-gfx-request@lists.freedesktop.org?subject=help>
List-Subscribe: <http://lists.freedesktop.org/mailman/listinfo/intel-gfx>,
	<mailto:intel-gfx-request@lists.freedesktop.org?subject=subscribe>
Sender: intel-gfx-bounces+gcfxdi-intel-gfx=m.gmane.org@lists.freedesktop.org
Errors-To: intel-gfx-bounces+gcfxdi-intel-gfx=m.gmane.org@lists.freedesktop.org
To: Kees Cook <keescook@chromium.org>
Cc: intel-gfx@lists.freedesktop.org
List-Id: intel-gfx@lists.freedesktop.org

Kees Cook <keescook@chromium.org> writes:

> On Thu, Apr 11, 2013 at 9:15 AM, Mika Kuoppala
> <mika.kuoppala@linux.intel.com> wrote:
>> Kees Cook <keescook@chromium.org> writes:
>>
>>> On Thu, Apr 11, 2013 at 6:22 AM, Mika Kuoppala
>>> <mika.kuoppala@linux.intel.com> wrote:
>>>> commit 647416f9eefe7699754b01b9fc82758fde83248c
>>>> Author: Kees Cook <keescook@chromium.org>
>>>> Date:   Sun Mar 10 14:10:06 2013 -0700
>>>>
>>>>     drm/i915: use simple attribute in debugfs routines
>>>>
>>>> made i915_next_seqno debugfs entry to crop it's output
>>>> if returned value was large enough. Using simple_attr
>>>> will limit the output to 24 bytes. Fix this by returning
>>>> only the value and nothing else.
>>>>
>>>> Cc: Kees Cook <keescook@chromium.org>
>>>> Signed-off-by: Mika Kuoppala <mika.kuoppala@intel.com>
>>>
>>> Oh! Thanks for catching that. What a weird limitation.
>>>
>>> What about max freq, min freq, and wedged? Do those run the risk of
>>> truncation too?
>>
>> max and min freq should be safe, and wedged too on 32bit platforms.
>> But if gpu is declared wedged on host with 64bit atomic_t,
>> it will crop the output.
>
> Should we consider proposing an increase in the size of the simple
> attr buffer? It seems silly to provide an arbitrary format string but
> leave the buffer so small.

That or dynamic allocation to attr->get_buf. But that would need
extra pass with snprintf and I don't know if that qualifies as 'simple'
anymore.

I have posted a patch which fixes all i915 debugfs simple attributes
to fit into the simple_attr by removing everything except the fmt to
value. I didn't find any testcases which would rely on preample
being there.

--Mika