[PATCH 3.16 15/16] KVM: nVMX: unconditionally cancel preemption timer in free_nested (CVE-2019-7221)

[Ben Hutchings <ben@decadent.org.uk>]

3.16.64-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Peter Shier <pshier@google.com>

commit ecec76885bcfe3294685dc363fd1273df0d5d65f upstream.

Bugzilla: 1671904

There are multiple code paths where an hrtimer may have been started to
emulate an L1 VMX preemption timer that can result in a call to free_nested
without an intervening L2 exit where the hrtimer is normally
cancelled. Unconditionally cancel in free_nested to cover all cases.

Embargoed until Feb 7th 2019.

Signed-off-by: Peter Shier <pshier@google.com>
Reported-by: Jim Mattson <jmattson@google.com>
Reviewed-by: Jim Mattson <jmattson@google.com>
Reported-by: Felix Wilhelm <fwilhelm@google.com>
Message-Id: <20181011184646.154065-1-pshier@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
[bwh: Backported to 3.16: adjust filename, context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
 arch/x86/kvm/vmx.c | 1 +
 1 file changed, 1 insertion(+)

--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -6169,6 +6169,7 @@ static void free_nested(struct vcpu_vmx
 {
 	if (!vmx->nested.vmxon)
 		return;
+	hrtimer_cancel(&vmx->nested.preemption_timer);
 	vmx->nested.vmxon = false;
 	if (vmx->nested.current_vmptr != -1ull) {
 		nested_release_vmcs12(vmx);