On Wed, Oct 2, 2013 at 10:49 AM, Stephane Eranian <eran...@google.com> wrote: > On Wed, Oct 2, 2013 at 7:29 PM, Kees Cook <keesc...@chromium.org> wrote: >> 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? >> > Each time that vm_mm is allocated we would allocate a new generation > number.
Seems like a simple enough solution. Surely there must be a catch. :) > > Uniqueness is across processes. But that's by construction of the > address space. Okay, that's what I figured. -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/
