From: Wanpeng Li <wanpengli@xxxxxxxxxxx> Reported by syzkaller: #PF: supervisor write access in kernel mode #PF: error_code(0x0002) - not-present page PGD 403c01067 P4D 403c01067 PUD 0 Oops: 0002 [#1] SMP PTI CPU: 1 PID: 12564 Comm: a.out Tainted: G OE 5.3.0-rc4+ #4 RIP: 0010:coalesced_mmio_write+0xcc/0x130 [kvm] Call Trace: __kvm_io_bus_write+0x91/0xe0 [kvm] kvm_io_bus_write+0x79/0xf0 [kvm] write_mmio+0xae/0x170 [kvm] emulator_read_write_onepage+0x252/0x430 [kvm] emulator_read_write+0xcd/0x180 [kvm] emulator_write_emulated+0x15/0x20 [kvm] segmented_write+0x59/0x80 [kvm] writeback+0x113/0x250 [kvm] x86_emulate_insn+0x78c/0xd80 [kvm] x86_emulate_instruction+0x386/0x7c0 [kvm] kvm_mmu_page_fault+0xf9/0x9e0 [kvm] handle_ept_violation+0x10a/0x220 [kvm_intel] vmx_handle_exit+0xbe/0x6b0 [kvm_intel] vcpu_enter_guest+0x4dc/0x18d0 [kvm] kvm_arch_vcpu_ioctl_run+0x407/0x660 [kvm] kvm_vcpu_ioctl+0x3ad/0x690 [kvm] do_vfs_ioctl+0xa2/0x690 ksys_ioctl+0x6d/0x80 __x64_sys_ioctl+0x1a/0x20 do_syscall_64+0x74/0x720 entry_SYSCALL_64_after_hwframe+0x49/0xbe RIP: 0010:coalesced_mmio_write+0xcc/0x130 [kvm] Both the coalesced_mmio ring buffer indexs ring->first and ring->last are bigger than KVM_COALESCED_MMIO_MAX from the testcase, array out-of-bounds access triggers by ring->coalesced_mmio[ring->last].phys_addr = addr; assignment. This patch fixes it by mod indexs by KVM_COALESCED_MMIO_MAX. syzkaller source: https://syzkaller.appspot.com/x/repro.c?x=134b2826a00000 Reported-by: syzbot+983c866c3dd6efa3662a@xxxxxxxxxxxxxxxxxxxxxxxxx Cc: stable@xxxxxxxxxxxxxxx Signed-off-by: Wanpeng Li <wanpengli@xxxxxxxxxxx> --- virt/kvm/coalesced_mmio.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/virt/kvm/coalesced_mmio.c b/virt/kvm/coalesced_mmio.c index 5294abb..cff1ec9 100644 --- a/virt/kvm/coalesced_mmio.c +++ b/virt/kvm/coalesced_mmio.c @@ -73,6 +73,8 @@ static int coalesced_mmio_write(struct kvm_vcpu *vcpu, spin_lock(&dev->kvm->ring_lock); + ring->first = ring->first % KVM_COALESCED_MMIO_MAX; + ring->last = ring->last % KVM_COALESCED_MMIO_MAX; if (!coalesced_mmio_has_room(dev)) { spin_unlock(&dev->kvm->ring_lock); return -EOPNOTSUPP; -- 2.7.4
