KVM: arm/arm64: fix races in kvm_psci_vcpu_on

Fix potential races in kvm_psci_vcpu_on() by taking the kvm->lock
mutex.  In general, it's a bad idea to allow more than one PSCI_CPU_ON
to process the same target VCPU at the same time.  One such problem
that may arise is that one PSCI_CPU_ON could be resetting the target
vcpu, which fills the entire sys_regs array with a temporary value
including the MPIDR register, while another looks up the VCPU based
on the MPIDR value, resulting in no target VCPU found.  Resolves both
races found with the kvm-unit-tests/arm/psci unit test.

Reviewed-by: Marc Zyngier <marc.zyngier@arm.com>
Reviewed-by: Christoffer Dall <cdall@linaro.org>
Reported-by: Levente Kurusa <lkurusa@redhat.com>
Suggested-by: Christoffer Dall <cdall@linaro.org>
Signed-off-by: Andrew Jones <drjones@redhat.com>
Cc: stable@vger.kernel.org
Signed-off-by: Christoffer Dall <cdall@linaro.org>

diff --git a/arch/arm/kvm/psci.c b/arch/arm/kvm/psci.c
index c2b131527a643f6e6808b78f8c53e9751d0f71a9..a08d7a93aebbece7777f042ec3881ad088104a4d 100644 (file)
--- a/arch/arm/kvm/psci.c
+++ b/arch/arm/kvm/psci.c
@@ -208,9 +208,10 @@ int kvm_psci_version(struct kvm_vcpu *vcpu)
 
 static int kvm_psci_0_2_call(struct kvm_vcpu *vcpu)
 {
-       int ret = 1;
+       struct kvm *kvm = vcpu->kvm;
        unsigned long psci_fn = vcpu_get_reg(vcpu, 0) & ~((u32) 0);
        unsigned long val;
+       int ret = 1;
 
        switch (psci_fn) {
        case PSCI_0_2_FN_PSCI_VERSION:
@@ -230,7 +231,9 @@ static int kvm_psci_0_2_call(struct kvm_vcpu *vcpu)
                break;
        case PSCI_0_2_FN_CPU_ON:
        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:
        case PSCI_0_2_FN64_AFFINITY_INFO:
@@ -279,6 +282,7 @@ static int kvm_psci_0_2_call(struct kvm_vcpu *vcpu)
 
 static int kvm_psci_0_1_call(struct kvm_vcpu *vcpu)
 {
+       struct kvm *kvm = vcpu->kvm;
        unsigned long psci_fn = vcpu_get_reg(vcpu, 0) & ~((u32) 0);
        unsigned long val;
 
@@ -288,7 +292,9 @@ static int kvm_psci_0_1_call(struct kvm_vcpu *vcpu)
                val = PSCI_RET_SUCCESS;
                break;
        case KVM_PSCI_FN_CPU_ON:
+               mutex_lock(&kvm->lock);
                val = kvm_psci_vcpu_on(vcpu);
+               mutex_unlock(&kvm->lock);
                break;
        default:
                val = PSCI_RET_NOT_SUPPORTED;