Patch "KVM: arm/arm64: fix races in kvm_psci_vcpu_on" has been added to the 4.9-stable tree

This is a note to let you know that I've just added the patch titled

KVM: arm/arm64: fix races in kvm_psci_vcpu_on

to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
kvm-arm-arm64-fix-races-in-kvm_psci_vcpu_on.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Andrew Jones <[email protected]>
Date: Tue, 18 Apr 2017 17:59:58 +0200
Subject: KVM: arm/arm64: fix races in kvm_psci_vcpu_on

From: Andrew Jones <[email protected]>

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.

---
 arch/arm/kvm/psci.c |    8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

@@ -208,9 +208,10 @@ 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_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_
 		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_
 
 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_
 		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;

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/kvm-arm-arm64-fix-races-in-kvm_psci_vcpu_on.patch