On Wed, Oct 2, 2013 at 7:29 PM, Kees Cook <[email protected]> wrote: > On Wed, Oct 2, 2013 at 10:20 AM, Stephane Eranian <[email protected]> wrote: >> On Wed, Oct 2, 2013 at 7:14 PM, Kees Cook <[email protected]> wrote: >>> On Wed, Oct 2, 2013 at 6:37 AM, Peter Zijlstra <[email protected]> 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 <[email protected]> >>>>> 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 <[email protected]> >>>>> >> 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.
Uniqueness is across processes. But that's by construction of the address space. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
