Messages in this thread | | | Date | Wed, 2 Oct 2013 14:39:53 +0200 | From | Ingo Molnar <> | Subject | Re: [RFC] perf: mmap2 not covering VM_CLONE regions |
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* Peter Zijlstra <peterz@infradead.org> wrote:
> On Wed, Oct 02, 2013 at 01:23:16PM +0200, Peter Zijlstra wrote: > > > So the only thing I can come up with is something like the below; > > supposedly the sha hash mixing a boot time random seed and the mm > > pointer is enough to avoid it being a data leak. > > That is, right until it becomes feasible to run 2^64 SHA1 computations. > I've actually no idea how hard that is given todays GPU assisted > efforts.
Well, here are the possible cryptanalytic attacks I can think of:
- differential, because here you don't just have access to the hash value but you can essentially feed highly correlated plaintext to the hash at will, by starting/stopping threads, knowing their typical mm pointer differences, etc.
I.e. less than 2^64, potentially a lot less.
- 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.
But then again, how realistic is an attack? All that effort just to recover the raw kernel data pointer value of a struct mm? Dunno whether we should worry about it.
Thanks,
Ingo
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