[PATCH 3.16 066/134] KVM: arm/arm64: fix races in kvm_psci_vcpu_on

Ben Hutchings
2017-08-18T13:15:47Z

From: Andrew Jones <drjones@redhat.com>

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: Ben Hutchings <ben@decadent.org.uk>
---
arch/arm/kvm/psci.c | 8 +++++++-
1 file changed, 7 insertions(+), 1 deletion(-)

--- a/arch/arm/kvm/psci.c
+++ b/arch/arm/kvm/psci.c
@@ -191,9 +191,10 @@ int kvm_psci_version(struct kvm_vcpu *vc

static int kvm_psci_0_2_call(struct kvm_vcpu *vcpu)
{
- int ret = 1;
+ struct kvm *kvm = vcpu->kvm;
unsigned long psci_fn = *vcpu_reg(vcpu, 0) & ~((u32) 0);
unsigned long val;
+ int ret = 1;

switch (psci_fn) {
case PSCI_0_2_FN_PSCI_VERSION:
@@ -213,7 +214,9 @@ static int kvm_psci_0_2_call(struct kvm_
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:
@@ -269,6 +272,7 @@ static int kvm_psci_0_2_call(struct kvm_

static int kvm_psci_0_1_call(struct kvm_vcpu *vcpu)
{
+ struct kvm *kvm = vcpu->kvm;
unsigned long psci_fn = *vcpu_reg(vcpu, 0) & ~((u32) 0);
unsigned long val;

@@ -278,7 +282,9 @@ static int kvm_psci_0_1_call(struct kvm_
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;