KVM: coalesced_mmio: add bounds checking
diff mbox series

Message ID 1568815302-21319-1-git-send-email-pbonzini@redhat.com
State Accepted
Commit b60fe990c6b07ef6d4df67bc0530c7c90a62623a
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Series
  • KVM: coalesced_mmio: add bounds checking
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Commit Message

Paolo Bonzini Sept. 18, 2019, 2:01 p.m. UTC
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(-)

Comments

Greg Kroah-Hartman Sept. 18, 2019, 2:09 p.m. UTC | #1
On Wed, Sep 18, 2019 at 04:01:42PM +0200, Paolo Bonzini wrote:
> 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(-)

Also looks good to me.

Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Will Deacon Sept. 18, 2019, 3:20 p.m. UTC | #2
On Wed, Sep 18, 2019 at 04:01:42PM +0200, Paolo Bonzini wrote:
> 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(-)

Acked-by: Will Deacon <will@kernel.org>

Will

Patch
diff mbox series

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;
 }