linux-kernel - Re: [REPOST PATCH 1/8] fence: dma-buf cross-device synchronization (v17)

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Date:	Fri, 20 Jun 2014 10:24:15 +0200
From:	Daniel Vetter <daniel@...ll.ch>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Greg KH <gregkh@...uxfoundation.org>,
	Rob Clark <robdclark@...il.com>,
	Maarten Lankhorst <maarten.lankhorst@...onical.com>,
	"open list:GENERIC INCLUDE/A..." <linux-arch@...r.kernel.org>,
	Thomas Hellstrom <thellstrom@...are.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
	"linaro-mm-sig@...ts.linaro.org" <linaro-mm-sig@...ts.linaro.org>,
	Thierry Reding <thierry.reding@...il.com>,
	Colin Cross <ccross@...gle.com>,
	Sumit Semwal <sumit.semwal@...aro.org>,
	"linux-media@...r.kernel.org" <linux-media@...r.kernel.org>
Subject: Re: [REPOST PATCH 1/8] fence: dma-buf cross-device synchronization (v17)

On Fri, Jun 20, 2014 at 12:39 AM, H. Peter Anvin <hpa@...or.com> wrote:
>>> Aside: This is a pet peeve of mine and recently I've switched to
>>> rejecting all patch that have a BUG_ON, period.
>>
>> Please do, I have been for a few years now as well for the same reasons
>> you cite.
>>
>
> I'm actually concerned about this trend.  Downgrading things to WARN_ON
> can allow a security bug in the kernel to continue to exist, for
> example, or make the error message disappear.
>
> I am wondering if the right thing here isn't to have a user (command
> line?) settable policy as to how to proceed on an assert violation,
> instead of hardcoding it at compile time.

I should clarify: If it smells like the issue is a failure of our
ioctl/syscall validation code to catch crap, BUG_ON is the right
choice. And fundamentally I've had this rule since 1-2 years now, the
only recent change I've done is switch my scripts from warning by
default if there's a new BUG_ON to rejecting by default. Mostly
because I'm lazy and let too many BUG_ONs pass through by default.

Also if you add a new interface to i915 I'll make damn sure you supply
a full set of nasty testcases to abuse the ioctl hard. In the end it's
a tradeoff and overall I don't think I'm compromising security with my
current set of rules.

Also, people don't (yet) terribly care about data integrity as soon as
their data has passed once through a gpu.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch
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