kvm: x86: fix stale mmio cache bug

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.

Cc: [email protected]
Signed-off-by: David Matlack <[email protected]>
[xiaoguangrong: adjust the code to make it simpler for stable-tree fix.]
Signed-off-by: Xiao Guangrong <[email protected]>
Reviewed-by: David Matlack <[email protected]>
Reviewed-by: Xiao Guangrong <[email protected]>
Tested-by: David Matlack <[email protected]>
Signed-off-by: Paolo Bonzini <[email protected]>

0 files changed, 0 insertions, 0 deletions