From 52cb3fd60ec0a1c9b61cd28bae4e8c1d377e7b60 Mon Sep 17 00:00:00 2001 From: Matt Delco Date: Mon, 16 Sep 2019 14:16:54 -0700 Subject: [PATCH] KVM: coalesced_mmio: add bounds checking commit b60fe990c6b07ef6d4df67bc0530c7c90a62623a upstream. 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 Signed-off-by: Jim Mattson Reported-by: syzbot+983c866c3dd6efa3662a@syzkaller.appspotmail.com [Use READ_ONCE. - Paolo] Signed-off-by: Paolo Bonzini Signed-off-by: Greg Kroah-Hartman --- virt/kvm/coalesced_mmio.c | 17 ++++++++++------- 1 file changed, 10 insertions(+), 7 deletions(-) diff --git a/virt/kvm/coalesced_mmio.c b/virt/kvm/coalesced_mmio.c index 571c1ce37d15..5c1efb869df2 100644 --- a/virt/kvm/coalesced_mmio.c +++ b/virt/kvm/coalesced_mmio.c @@ -39,7 +39,7 @@ 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; @@ -51,7 +51,7 @@ 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; @@ -66,24 +66,27 @@ 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[insert].phys_addr = addr; + ring->coalesced_mmio[insert].len = len; + memcpy(ring->coalesced_mmio[insert].data, val, len); 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; } -- 2.20.1