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Date:	Fri, 20 Jun 2014 10:24:15 +0200
From:	Daniel Vetter <>
To:	"H. Peter Anvin" <>
Cc:	Greg KH <>,
	Rob Clark <>,
	Maarten Lankhorst <>,
	"open list:GENERIC INCLUDE/A..." <>,
	Thomas Hellstrom <>,
	Linux Kernel Mailing List <>,
	"" <>,
	"" <>,
	Thierry Reding <>,
	Colin Cross <>,
	Sumit Semwal <>,
	"" <>
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 <> 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 Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 -
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