KVM: arm/arm64: fix races in kvm_psci_vcpu_on

commit 6c7a5dce22b3f3cc44be098e2837fa6797edb8b8 upstream.

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>
Signed-off-by: Christoffer Dall <cdall@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 7 insertions, 1 deletions

diff --git a/arch/arm/kvm/psci.c b/arch/arm/kvm/psci.c
index c2b131527a64..a08d7a93aebb 100644
--- 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;