On Wed, Oct 2, 2013 at 10:20 AM, Stephane Eranian <eran...@google.com> wrote: > On Wed, Oct 2, 2013 at 7:14 PM, Kees Cook <keesc...@chromium.org> wrote: >> On Wed, Oct 2, 2013 at 6:37 AM, Peter Zijlstra <pet...@infradead.org> wrote: >>> On Wed, Oct 02, 2013 at 03:13:16PM +0200, Stephane Eranian wrote: >>>> On Wed, Oct 2, 2013 at 3:01 PM, Peter Zijlstra <pet...@infradead.org> >>>> 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 <pet...@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 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: >>>> >> >>>> >> $ perf record -e cycles ...... >>>> >> >>>> >> In per-thread mode and collect kernel level addresses. >>>> > >>>> > 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. >> >> We already have other kernel address leaks (e.g. heap addresses via >> INET_DIAG), and I'd like to avoid adding more. It'd be nice if there >> was a common way to uniquely mask these values that are really just >> "handles". We could use it both here and in the network code. >> >> Would it be possible to just have a "regular" incrementing handle, >> like fd, or are we talking about doing that map for all VMAs, which >> would make that mapping unfeasible due to storage needs? >> > All we need is a way to report that two vmas point to the same > vma->vm_mm, i..e, same physical data. If I understand what > you are suggesting, you'd add some sort of generation number > to the vm_mm. Each new vm_mm gets a new number. That > would work, I think. No kernel addresses reported directly nor > hashed.
Right. Is that workable? It sounds like this handle is only needed at inspection time, though. Is this uniqueness test limited to a single process, or is this uniqueness test across processes? -Kees -- Kees Cook Chrome OS Security -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
