netdev - Re: [PATCH] Prevent reading uninitialized memory with socketfilters

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Date:	Wed, 10 Nov 2010 21:25:43 +0000
From:	Ben Hutchings <bhutchings@...arflare.com>
To:	David Miller <davem@...emloft.net>
Cc:	penguin-kernel@...ove.SAKURA.ne.jp, eric.dumazet@...il.com,
	netdev@...r.kernel.org
Subject: Re: [PATCH] Prevent reading uninitialized memory with socketfilters

On Wed, 2010-11-10 at 12:59 -0800, David Miller wrote:
> From: Ben Hutchings <bhutchings@...arflare.com>
> Date: Wed, 10 Nov 2010 20:57:44 +0000
> 
> > On Wed, 2010-11-10 at 10:39 -0800, David Miller wrote:
> > [...]
> >> In this patch, I use a bitmap (a single long var) so that only filters
> >> using mem[] loads/stores pay the price of added security checks.
> >> 
> >> For other filters, additional cost is a single instruction.
> >> 
> >> [ Since we access fentry->k a lot now, cache it in a local variable
> >>   and mark filter entry pointer as const. -DaveM ]
> > [...]
> > 
> > I don't see the justification for combining these changes.  One patch,
> > one fix, right?
> 
> I'm minimizing the performance impact of the new bitmap checks.

This seems like an entirely separate optimisation, since fentry->k was
*already* being used all over the place.  (And a smart compiler should
optimise that anyway... though I realise gcc is often not that smart.)

Ben.

-- 
Ben Hutchings, Senior Software Engineer, Solarflare Communications
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.

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