Re: [RFC] perf: mmap2 not covering VM_CLONE regions

[Peter Zijlstra]

On Wed, Oct 02, 2013 at 03:13:16PM +0200, Stephane Eranian wrote:
> On Wed, Oct 2, 2013 at 3:01 PM, Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
> > On Wed, Oct 02, 2013 at 02:59:32PM +0200, Stephane Eranian wrote:
> >> On Wed, Oct 2, 2013 at 2:46 PM, Peter Zijlstra <peterz@xxxxxxxxxxxxx> 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 was going to say just that. But that's not the default, paranoid level
> >> is at 1 by default and not 2. So I supposedly can still do:
> >
> > Oh right you are.. so yes that's a very viable avenue.
> 
> You mean simply encoding the vma->vm_mm as the ino number, for instance.

Nah.. I think Kees would very much shoot us on the spot for doing that.
But with the paranoid level defaulting to 1 the PMU attack on the kernel
SHA implenentation is feasible.

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