KVM: arm64: PSCI: Narrow input registers when using 32bit functions

When a guest delibarately uses an SMC32 function number (which is allowed),
we should make sure we drop the top 32bits from the input arguments, as they
could legitimately be junk.

Reported-by: Christoffer Dall <christoffer.dall@arm.com>
Reviewed-by: Christoffer Dall <christoffer.dall@arm.com>
Reviewed-by: Alexandru Elisei <alexandru.elisei@arm.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>

diff --git a/virt/kvm/arm/psci.c b/virt/kvm/arm/psci.c
index 14a162e..3772717 100644 (file)
--- a/virt/kvm/arm/psci.c
+++ b/virt/kvm/arm/psci.c
@@ -186,6 +186,18 @@ static void kvm_psci_system_reset(struct kvm_vcpu *vcpu)
        kvm_prepare_system_event(vcpu, KVM_SYSTEM_EVENT_RESET);
 }
 
+static void kvm_psci_narrow_to_32bit(struct kvm_vcpu *vcpu)
+{
+       int i;
+
+       /*
+        * Zero the input registers' upper 32 bits. They will be fully
+        * zeroed on exit, so we're fine changing them in place.
+        */
+       for (i = 1; i < 4; i++)
+               vcpu_set_reg(vcpu, i, lower_32_bits(vcpu_get_reg(vcpu, i)));
+}
+
 static int kvm_psci_0_2_call(struct kvm_vcpu *vcpu)
 {
        struct kvm *kvm = vcpu->kvm;
@@ -210,12 +222,16 @@ static int kvm_psci_0_2_call(struct kvm_vcpu *vcpu)
                val = PSCI_RET_SUCCESS;
                break;
        case PSCI_0_2_FN_CPU_ON:
+               kvm_psci_narrow_to_32bit(vcpu);
+               fallthrough;
        case PSCI_0_2_FN64_CPU_ON:
                mutex_lock(&kvm->lock);
                val = kvm_psci_vcpu_on(vcpu);
                mutex_unlock(&kvm->lock);
                break;
        case PSCI_0_2_FN_AFFINITY_INFO:
+               kvm_psci_narrow_to_32bit(vcpu);
+               fallthrough;
        case PSCI_0_2_FN64_AFFINITY_INFO:
                val = kvm_psci_vcpu_affinity_info(vcpu);
                break;