linux-kernel - [PATCH 4.10 28/93] KVM: arm/arm64: fix races in kvm_psci_vcpu

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Date:   Thu, 18 May 2017 12:46:57 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Marc Zyngier <marc.zyngier@....com>,
        Christoffer Dall <cdall@...aro.org>,
        Levente Kurusa <lkurusa@...hat.com>,
        Andrew Jones <drjones@...hat.com>
Subject: [PATCH 4.10 28/93] KVM: arm/arm64: fix races in kvm_psci_vcpu_on

4.10-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Andrew Jones <drjones@...hat.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@....com>
Reviewed-by: Christoffer Dall <cdall@...aro.org>
Reported-by: Levente Kurusa <lkurusa@...hat.com>
Suggested-by: Christoffer Dall <cdall@...aro.org>
Signed-off-by: Andrew Jones <drjones@...hat.com>
Signed-off-by: Christoffer Dall <cdall@...aro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 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
@@ -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;