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: Andy Honig <ahonig@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index b84ba4b17757aed24d0385ae7211b80985b61eb6..7ffc224bbe4127a90ef7741f09ae94f75e17feec 100644 (file)
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -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;
 }