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Commit 0185604c authored by Andrew Honig's avatar Andrew Honig Committed by Paolo Bonzini
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KVM: x86: Reload pit counters for all channels when restoring state 



Currently if userspace restores the pit counters with a count of 0
on channels 1 or 2 and the guest attempts to read the count on those
channels, then KVM will perform a mod of 0 and crash.  This will ensure
that 0 values are converted to 65536 as per the spec.

This is CVE-2015-7513.

Signed-off-by: default avatarAndy Honig <ahonig@google.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent e24dea2a

arch/x86/kvm/x86.c

+6 −2
Original line number Diff line number Diff line
@@ -3572,9 +3572,11 @@ static int kvm_vm_ioctl_get_pit(struct kvm *kvm, struct kvm_pit_state *ps) 


static int kvm_vm_ioctl_set_pit(struct kvm *kvm, struct kvm_pit_state *ps)

{

	int i;

	mutex_lock(&kvm->arch.vpit->pit_state.lock);

	memcpy(&kvm->arch.vpit->pit_state, ps, sizeof(struct kvm_pit_state));

	kvm_pit_load_count(kvm, 0, ps->channels[0].count, 0);

	for (i = 0; i < 3; i++)

		kvm_pit_load_count(kvm, i, ps->channels[i].count, 0);

	mutex_unlock(&kvm->arch.vpit->pit_state.lock);

	return 0;

}
@@ -3593,6 +3595,7 @@ static int kvm_vm_ioctl_get_pit2(struct kvm *kvm, struct kvm_pit_state2 *ps) 
static int kvm_vm_ioctl_set_pit2(struct kvm *kvm, struct kvm_pit_state2 *ps)

{

	int start = 0;

	int i;

	u32 prev_legacy, cur_legacy;

	mutex_lock(&kvm->arch.vpit->pit_state.lock);

	prev_legacy = kvm->arch.vpit->pit_state.flags & KVM_PIT_FLAGS_HPET_LEGACY;
@@ -3602,7 +3605,8 @@ static int kvm_vm_ioctl_set_pit2(struct kvm *kvm, struct kvm_pit_state2 *ps) 
	memcpy(&kvm->arch.vpit->pit_state.channels, &ps->channels,

	       sizeof(kvm->arch.vpit->pit_state.channels));

	kvm->arch.vpit->pit_state.flags = ps->flags;

	kvm_pit_load_count(kvm, 0, kvm->arch.vpit->pit_state.channels[0].count, start);

	for (i = 0; i < 3; i++)

		kvm_pit_load_count(kvm, i, kvm->arch.vpit->pit_state.channels[i].count, start);

	mutex_unlock(&kvm->arch.vpit->pit_state.lock);

	return 0;

}