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From: Oliver Upton <oupton@google.com>
To: kvm@vger.kernel.org, kvmarm@lists.cs.columbia.edu
Cc: Marc Zyngier <maz@kernel.org>, Peter Shier <pshier@google.com>,
	Ricardo Koller <ricarkol@google.com>,
	Jing Zhang <jingzhangos@google.com>,
	Raghavendra Rao Anata <rananta@google.com>,
	James Morse <james.morse@arm.com>,
	Alexandru Elisei <alexandru.elisei@arm.com>,
	Suzuki K Poulose <suzuki.poulose@arm.com>,
	Andrew Jones <drjones@redhat.com>,
	Oliver Upton <oupton@google.com>
Subject: [PATCH v2 1/4] KVM: arm64: Fix read-side race on updates to vcpu reset state
Date: Wed, 18 Aug 2021 20:21:30 +0000	[thread overview]
Message-ID: <20210818202133.1106786-2-oupton@google.com> (raw)
In-Reply-To: <20210818202133.1106786-1-oupton@google.com>

KVM correctly serializes writes to a vCPU's reset state, however since
we do not take the KVM lock on the read side it is entirely possible to
read state from two different reset requests.

Cure the race for now by taking the KVM lock when reading the
reset_state structure.

Fixes: 358b28f09f0a ("arm/arm64: KVM: Allow a VCPU to fully reset itself")
Signed-off-by: Oliver Upton <oupton@google.com>
---
 arch/arm64/kvm/reset.c | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/arch/arm64/kvm/reset.c b/arch/arm64/kvm/reset.c
index cba7872d69a8..d862441b03b1 100644
--- a/arch/arm64/kvm/reset.c
+++ b/arch/arm64/kvm/reset.c
@@ -210,10 +210,16 @@ static bool vcpu_allowed_register_width(struct kvm_vcpu *vcpu)
  */
 int kvm_reset_vcpu(struct kvm_vcpu *vcpu)
 {
+	struct vcpu_reset_state reset_state;
 	int ret;
 	bool loaded;
 	u32 pstate;
 
+	mutex_lock(&vcpu->kvm->lock);
+	reset_state = vcpu->arch.reset_state;
+	WRITE_ONCE(vcpu->arch.reset_state.reset, false);
+	mutex_unlock(&vcpu->kvm->lock);
+
 	/* Reset PMU outside of the non-preemptible section */
 	kvm_pmu_vcpu_reset(vcpu);
 
@@ -276,8 +282,8 @@ int kvm_reset_vcpu(struct kvm_vcpu *vcpu)
 	 * Additional reset state handling that PSCI may have imposed on us.
 	 * Must be done after all the sys_reg reset.
 	 */
-	if (vcpu->arch.reset_state.reset) {
-		unsigned long target_pc = vcpu->arch.reset_state.pc;
+	if (reset_state.reset) {
+		unsigned long target_pc = reset_state.pc;
 
 		/* Gracefully handle Thumb2 entry point */
 		if (vcpu_mode_is_32bit(vcpu) && (target_pc & 1)) {
@@ -286,13 +292,11 @@ int kvm_reset_vcpu(struct kvm_vcpu *vcpu)
 		}
 
 		/* Propagate caller endianness */
-		if (vcpu->arch.reset_state.be)
+		if (reset_state.be)
 			kvm_vcpu_set_be(vcpu);
 
 		*vcpu_pc(vcpu) = target_pc;
-		vcpu_set_reg(vcpu, 0, vcpu->arch.reset_state.r0);
-
-		vcpu->arch.reset_state.reset = false;
+		vcpu_set_reg(vcpu, 0, reset_state.r0);
 	}
 
 	/* Reset timer */
-- 
2.33.0.rc1.237.g0d66db33f3-goog


WARNING: multiple messages have this Message-ID (diff)
From: Oliver Upton <oupton@google.com>
To: kvm@vger.kernel.org, kvmarm@lists.cs.columbia.edu
Cc: Marc Zyngier <maz@kernel.org>, Peter Shier <pshier@google.com>,
	Raghavendra Rao Anata <rananta@google.com>
Subject: [PATCH v2 1/4] KVM: arm64: Fix read-side race on updates to vcpu reset state
Date: Wed, 18 Aug 2021 20:21:30 +0000	[thread overview]
Message-ID: <20210818202133.1106786-2-oupton@google.com> (raw)
In-Reply-To: <20210818202133.1106786-1-oupton@google.com>

KVM correctly serializes writes to a vCPU's reset state, however since
we do not take the KVM lock on the read side it is entirely possible to
read state from two different reset requests.

Cure the race for now by taking the KVM lock when reading the
reset_state structure.

Fixes: 358b28f09f0a ("arm/arm64: KVM: Allow a VCPU to fully reset itself")
Signed-off-by: Oliver Upton <oupton@google.com>
---
 arch/arm64/kvm/reset.c | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/arch/arm64/kvm/reset.c b/arch/arm64/kvm/reset.c
index cba7872d69a8..d862441b03b1 100644
--- a/arch/arm64/kvm/reset.c
+++ b/arch/arm64/kvm/reset.c
@@ -210,10 +210,16 @@ static bool vcpu_allowed_register_width(struct kvm_vcpu *vcpu)
  */
 int kvm_reset_vcpu(struct kvm_vcpu *vcpu)
 {
+	struct vcpu_reset_state reset_state;
 	int ret;
 	bool loaded;
 	u32 pstate;
 
+	mutex_lock(&vcpu->kvm->lock);
+	reset_state = vcpu->arch.reset_state;
+	WRITE_ONCE(vcpu->arch.reset_state.reset, false);
+	mutex_unlock(&vcpu->kvm->lock);
+
 	/* Reset PMU outside of the non-preemptible section */
 	kvm_pmu_vcpu_reset(vcpu);
 
@@ -276,8 +282,8 @@ int kvm_reset_vcpu(struct kvm_vcpu *vcpu)
 	 * Additional reset state handling that PSCI may have imposed on us.
 	 * Must be done after all the sys_reg reset.
 	 */
-	if (vcpu->arch.reset_state.reset) {
-		unsigned long target_pc = vcpu->arch.reset_state.pc;
+	if (reset_state.reset) {
+		unsigned long target_pc = reset_state.pc;
 
 		/* Gracefully handle Thumb2 entry point */
 		if (vcpu_mode_is_32bit(vcpu) && (target_pc & 1)) {
@@ -286,13 +292,11 @@ int kvm_reset_vcpu(struct kvm_vcpu *vcpu)
 		}
 
 		/* Propagate caller endianness */
-		if (vcpu->arch.reset_state.be)
+		if (reset_state.be)
 			kvm_vcpu_set_be(vcpu);
 
 		*vcpu_pc(vcpu) = target_pc;
-		vcpu_set_reg(vcpu, 0, vcpu->arch.reset_state.r0);
-
-		vcpu->arch.reset_state.reset = false;
+		vcpu_set_reg(vcpu, 0, reset_state.r0);
 	}
 
 	/* Reset timer */
-- 
2.33.0.rc1.237.g0d66db33f3-goog

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  reply	other threads:[~2021-08-18 20:21 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-18 20:21 [PATCH v2 0/4] KVM: arm64: Fix some races in CPU_ON PSCI call Oliver Upton
2021-08-18 20:21 ` Oliver Upton
2021-08-18 20:21 ` Oliver Upton [this message]
2021-08-18 20:21   ` [PATCH v2 1/4] KVM: arm64: Fix read-side race on updates to vcpu reset state Oliver Upton
2021-08-18 20:21 ` [PATCH v2 2/4] KVM: arm64: Handle PSCI resets before userspace touches vCPU state Oliver Upton
2021-08-18 20:21   ` Oliver Upton
2021-08-18 20:21 ` [PATCH v2 3/4] KVM: arm64: Enforce reserved bits for PSCI target affinities Oliver Upton
2021-08-18 20:21   ` Oliver Upton
2021-08-18 20:21 ` [PATCH v2 4/4] selftests: KVM: Introduce psci_cpu_on_test Oliver Upton
2021-08-18 20:21   ` Oliver Upton
2021-08-19  8:18 ` [PATCH v2 0/4] KVM: arm64: Fix some races in CPU_ON PSCI call Marc Zyngier
2021-08-19  8:18   ` Marc Zyngier

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