[PATCH 2/3] KVM: nVMX: unconditionally cancel preemption timer in free_nested (CVE-2019-7221)

[Tyler Hicks]

From: Peter Shier <pshier at google.com>

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 at google.com>
Reported-by: Jim Mattson <jmattson at google.com>
Reviewed-by: Jim Mattson <jmattson at google.com>
Reported-by: Felix Wilhelm <fwilhelm at google.com>
Cc: stable at kernel.org
Message-Id: <20181011184646.154065-1-pshier at google.com>
Signed-off-by: Paolo Bonzini <pbonzini at redhat.com>

CVE-2019-7221

(backported from commit ecec76885bcfe3294685dc363fd1273df0d5d65f)
[tyhicks: Backport to 4.18:
 - free_nested() is in arch/x86/kvm/vmx.c]
Signed-off-by: Tyler Hicks <tyhicks at canonical.com>
---
 arch/x86/kvm/vmx.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 7ade6cb125d3..37b095e7f00a 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -7681,6 +7681,7 @@ static void free_nested(struct vcpu_vmx *vmx)
 	if (!vmx->nested.vmxon && !vmx->nested.smm.vmxon)
 		return;
 
+	hrtimer_cancel(&vmx->nested.preemption_timer);
 	vmx->nested.vmxon = false;
 	vmx->nested.smm.vmxon = false;
 	free_vpid(vmx->nested.vpid02);
-- 
2.7.4