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authorMatt Delco <delco@chromium.org>2019-09-16 14:16:54 -0700
committerPaolo Bonzini <pbonzini@redhat.com>2019-09-18 15:56:55 +0200
commitb60fe990c6b07ef6d4df67bc0530c7c90a62623a (patch)
tree49d837232351e9b86c9632ccc509f26596e269ed /virt
parenta9c20bb0206ae9384bd470a6832dd8913730add9 (diff)
KVM: coalesced_mmio: add bounds checking
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>
Diffstat (limited to 'virt')
-rw-r--r--virt/kvm/coalesced_mmio.c19
1 files 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;
}

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