From: Matt Delco delco@chromium.org
The first/last indexes are typically shared with a user app. The app can change the 'last' index that the kernel uses to store the next result. This change sanity checks the index before using it for writing to a potentially arbitrary address.
This fixes CVE-2019-14821.
Cc: stable@vger.kernel.org Fixes: 5f94c1741bdc ("KVM: Add coalesced MMIO support (common part)") Signed-off-by: Matt Delco delco@chromium.org Signed-off-by: Jim Mattson jmattson@google.com Reported-by: syzbot+983c866c3dd6efa3662a@syzkaller.appspotmail.com [Use READ_ONCE. - Paolo] Signed-off-by: Paolo Bonzini pbonzini@redhat.com --- virt/kvm/coalesced_mmio.c | 19 +++++++++++-------- 1 file changed, 11 insertions(+), 8 deletions(-)
diff --git a/virt/kvm/coalesced_mmio.c b/virt/kvm/coalesced_mmio.c index 5294abb3f178..8ffd07e2a160 100644 --- a/virt/kvm/coalesced_mmio.c +++ b/virt/kvm/coalesced_mmio.c @@ -40,7 +40,7 @@ static int coalesced_mmio_in_range(struct kvm_coalesced_mmio_dev *dev, return 1; }
-static int coalesced_mmio_has_room(struct kvm_coalesced_mmio_dev *dev) +static int coalesced_mmio_has_room(struct kvm_coalesced_mmio_dev *dev, u32 last) { struct kvm_coalesced_mmio_ring *ring; unsigned avail; @@ -52,7 +52,7 @@ static int coalesced_mmio_has_room(struct kvm_coalesced_mmio_dev *dev) * there is always one unused entry in the buffer */ ring = dev->kvm->coalesced_mmio_ring; - avail = (ring->first - ring->last - 1) % KVM_COALESCED_MMIO_MAX; + avail = (ring->first - last - 1) % KVM_COALESCED_MMIO_MAX; if (avail == 0) { /* full */ return 0; @@ -67,25 +67,28 @@ static int coalesced_mmio_write(struct kvm_vcpu *vcpu, { struct kvm_coalesced_mmio_dev *dev = to_mmio(this); struct kvm_coalesced_mmio_ring *ring = dev->kvm->coalesced_mmio_ring; + __u32 insert;
if (!coalesced_mmio_in_range(dev, addr, len)) return -EOPNOTSUPP;
spin_lock(&dev->kvm->ring_lock);
- if (!coalesced_mmio_has_room(dev)) { + insert = READ_ONCE(ring->last); + if (!coalesced_mmio_has_room(dev, insert) || + insert >= KVM_COALESCED_MMIO_MAX) { spin_unlock(&dev->kvm->ring_lock); return -EOPNOTSUPP; }
/* copy data in first free entry of the ring */
- ring->coalesced_mmio[ring->last].phys_addr = addr; - ring->coalesced_mmio[ring->last].len = len; - memcpy(ring->coalesced_mmio[ring->last].data, val, len); - ring->coalesced_mmio[ring->last].pio = dev->zone.pio; + ring->coalesced_mmio[insert].phys_addr = addr; + ring->coalesced_mmio[insert].len = len; + memcpy(ring->coalesced_mmio[insert].data, val, len); + ring->coalesced_mmio[insert].pio = dev->zone.pio; smp_wmb(); - ring->last = (ring->last + 1) % KVM_COALESCED_MMIO_MAX; + ring->last = (insert + 1) % KVM_COALESCED_MMIO_MAX; spin_unlock(&dev->kvm->ring_lock); return 0; }