Re: [PATCH 2/2] kvm: x86: fix stale mmio cache bug

[David Matlack]

On Thu, Aug 14, 2014 at 12:01 AM, Xiao Guangrong
<xiaoguangrong@xxxxxxxxxxxxxxxxxx> wrote:
> From: David Matlack <dmatlack@xxxxxxxxxx>
>
> The following events can lead to an incorrect KVM_EXIT_MMIO bubbling
> up to userspace:
>
> (1) Guest accesses gpa X without a memory slot. The gfn is cached in
> struct kvm_vcpu_arch (mmio_gfn). On Intel EPT-enabled hosts, KVM sets
> the SPTE write-execute-noread so that future accesses cause
> EPT_MISCONFIGs.
>
> (2) Host userspace creates a memory slot via KVM_SET_USER_MEMORY_REGION
> covering the page just accessed.
>
> (3) Guest attempts to read or write to gpa X again. On Intel, this
> generates an EPT_MISCONFIG. The memory slot generation number that
> was incremented in (2) would normally take care of this but we fast
> path mmio faults through quickly_check_mmio_pf(), which only checks
> the per-vcpu mmio cache. Since we hit the cache, KVM passes a
> KVM_EXIT_MMIO up to userspace.
>
> This patch fixes the issue by using the memslot generation number
> to validate the mmio cache.
>
> [ xiaoguangrong: adjust the code to make it simpler for stable-tree fix. ]

The adjustments look good. Thanks!
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/