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