linux-kernel - Re: [RFC] perf: mmap2 not covering VM

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Message-ID: <20131002152210.GA15757@gmail.com>
Date:	Wed, 2 Oct 2013 17:22:10 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Stephane Eranian <eranian@...gle.com>,
	LKML <linux-kernel@...r.kernel.org>,
	"mingo@...e.hu" <mingo@...e.hu>,
	"ak@...ux.intel.com" <ak@...ux.intel.com>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	David Ahern <dsahern@...il.com>, Jiri Olsa <jolsa@...hat.com>,
	Hugh Dickins <hughd@...gle.com>,
	Kees Cook <keescook@...omium.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [RFC] perf: mmap2 not covering VM_CLONE regions


* Peter Zijlstra <peterz@...radead.org> wrote:

> On Wed, Oct 02, 2013 at 02:39:53PM +0200, Ingo Molnar wrote:
> >  - then there are timing attacks, and someone having access to a PMU
> >    context and who can trigger this SHA1 computation arbitrarily in task 
> >    local context can run very accurate and low noise timing attacks...
> > 
> >    I don't think the kernel's sha_transform() is hardened against timing 
> >    attacks, it's performance optimized so it has variable execution time
> >    highly dependent on plaintext input - which leaks information about the 
> >    plaintext.
> 
> Typical user doesn't have enough priv to profile kernel space; once you 
> do you also have enough priv to see kernel addresses outright (ie. 
> kallsyms etc..).

I didn't mean profiling - that's not a 'timing attack'.

A simple RDTSC done around repeated calls to sha_transform() using kernel 
functionality is.

Thanks,

	Ingo
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