[PATCH] KVM: arm64: kvm_reset_vcpu() return code incorrect with SVE

Subsystems: arm64 port (aarch64 architecture), kernel virtual machine for arm64 (kvm/arm64), the rest

STALE2277d

3 messages, 2 authors, 2020-06-17 · open the first message on its own page

[PATCH] KVM: arm64: kvm_reset_vcpu() return code incorrect with SVE

From: Steven Price <steven.price@arm.com>
Date: 2020-06-17 10:44:07

If SVE is enabled then 'ret' can be assigned the return value of
kvm_vcpu_enable_sve() which may be 0 causing future "goto out" sites to
erroneously return 0 on failure rather than -EINVAL as expected.

Remove the initialisation of 'ret' and make setting the return value
explicit to avoid this situation in the future.

Fixes: 9a3cdf26e336 ("KVM: arm64/sve: Allow userspace to enable SVE for vcpus")
Reported-by: James Morse <james.morse@arm.com>
Signed-off-by: Steven Price <steven.price@arm.com>
---
The problematic chunk isn't visible in the diff, so reproduced here:

	if (!kvm_arm_vcpu_sve_finalized(vcpu)) {
		if (test_bit(KVM_ARM_VCPU_SVE, vcpu->arch.features)) {
			ret = kvm_vcpu_enable_sve(vcpu);
			if (ret)
				goto out;
		}
	} else {
		kvm_vcpu_reset_sve(vcpu);
	}

 arch/arm64/kvm/reset.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/kvm/reset.c b/arch/arm64/kvm/reset.c
index d3b209023727..f1057603b756 100644
--- a/arch/arm64/kvm/reset.c
+++ b/arch/arm64/kvm/reset.c

@@ -245,7 +245,7 @@ static int kvm_vcpu_enable_ptrauth(struct kvm_vcpu *vcpu)
  */
 int kvm_reset_vcpu(struct kvm_vcpu *vcpu)
 {
-	int ret = -EINVAL;
+	int ret;
 	bool loaded;
 	u32 pstate;

@@ -269,15 +269,19 @@ int kvm_reset_vcpu(struct kvm_vcpu *vcpu)
 
 	if (test_bit(KVM_ARM_VCPU_PTRAUTH_ADDRESS, vcpu->arch.features) ||
 	    test_bit(KVM_ARM_VCPU_PTRAUTH_GENERIC, vcpu->arch.features)) {
-		if (kvm_vcpu_enable_ptrauth(vcpu))
+		if (kvm_vcpu_enable_ptrauth(vcpu)) {
+			ret = -EINVAL;
 			goto out;
+		}
 	}
 
 	switch (vcpu->arch.target) {
 	default:
 		if (test_bit(KVM_ARM_VCPU_EL1_32BIT, vcpu->arch.features)) {
-			if (!cpus_have_const_cap(ARM64_HAS_32BIT_EL1))
+			if (cpus_have_const_cap(ARM64_HAS_32BIT_EL1)) {
+				ret = -EINVAL;
 				goto out;
+			}
 			pstate = VCPU_RESET_PSTATE_SVC;
 		} else {
 			pstate = VCPU_RESET_PSTATE_EL1;

-- 
2.20.1


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Re: [PATCH] KVM: arm64: kvm_reset_vcpu() return code incorrect with SVE

From: Marc Zyngier <maz@kernel.org>
Date: 2020-06-17 10:47:51

Hi Steven,

On 2020-06-17 11:43, Steven Price wrote:

quoted hunk

If SVE is enabled then 'ret' can be assigned the return value of
kvm_vcpu_enable_sve() which may be 0 causing future "goto out" sites to
erroneously return 0 on failure rather than -EINVAL as expected.

Remove the initialisation of 'ret' and make setting the return value
explicit to avoid this situation in the future.

Fixes: 9a3cdf26e336 ("KVM: arm64/sve: Allow userspace to enable SVE for 
vcpus")
Reported-by: James Morse <james.morse@arm.com>
Signed-off-by: Steven Price <steven.price@arm.com>
---
The problematic chunk isn't visible in the diff, so reproduced here:

	if (!kvm_arm_vcpu_sve_finalized(vcpu)) {
		if (test_bit(KVM_ARM_VCPU_SVE, vcpu->arch.features)) {
			ret = kvm_vcpu_enable_sve(vcpu);
			if (ret)
				goto out;
		}
	} else {
		kvm_vcpu_reset_sve(vcpu);
	}

 arch/arm64/kvm/reset.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/kvm/reset.c b/arch/arm64/kvm/reset.c
index d3b209023727..f1057603b756 100644
--- a/arch/arm64/kvm/reset.c
+++ b/arch/arm64/kvm/reset.c

@@ -245,7 +245,7 @@ static int kvm_vcpu_enable_ptrauth(struct kvm_vcpu

*vcpu)
  */
 int kvm_reset_vcpu(struct kvm_vcpu *vcpu)
 {
-	int ret = -EINVAL;
+	int ret;
 	bool loaded;
 	u32 pstate;

@@ -269,15 +269,19 @@ int kvm_reset_vcpu(struct kvm_vcpu *vcpu)

 	if (test_bit(KVM_ARM_VCPU_PTRAUTH_ADDRESS, vcpu->arch.features) ||
 	    test_bit(KVM_ARM_VCPU_PTRAUTH_GENERIC, vcpu->arch.features)) {
-		if (kvm_vcpu_enable_ptrauth(vcpu))
+		if (kvm_vcpu_enable_ptrauth(vcpu)) {
+			ret = -EINVAL;
 			goto out;
+		}
 	}

 	switch (vcpu->arch.target) {
 	default:
 		if (test_bit(KVM_ARM_VCPU_EL1_32BIT, vcpu->arch.features)) {
-			if (!cpus_have_const_cap(ARM64_HAS_32BIT_EL1))
+			if (cpus_have_const_cap(ARM64_HAS_32BIT_EL1)) {

Do you really mean this? Seems counter-productive... :-(

+				ret = -EINVAL;
 				goto out;
+			}
 			pstate = VCPU_RESET_PSTATE_SVC;
 		} else {
 			pstate = VCPU_RESET_PSTATE_EL1;

Thanks,

         M.
-- 
Jazz is not dead. It just smells funny...

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Re: [PATCH] KVM: arm64: kvm_reset_vcpu() return code incorrect with SVE

From: Steven Price <steven.price@arm.com>
Date: 2020-06-17 10:50:24

On 17/06/2020 11:47, Marc Zyngier wrote:

Hi Steven,

On 2020-06-17 11:43, Steven Price wrote:

quoted

If SVE is enabled then 'ret' can be assigned the return value of
kvm_vcpu_enable_sve() which may be 0 causing future "goto out" sites to
erroneously return 0 on failure rather than -EINVAL as expected.

Remove the initialisation of 'ret' and make setting the return value
explicit to avoid this situation in the future.

Fixes: 9a3cdf26e336 ("KVM: arm64/sve: Allow userspace to enable SVE 
for vcpus")
Reported-by: James Morse <james.morse@arm.com>
Signed-off-by: Steven Price <steven.price@arm.com>
---
The problematic chunk isn't visible in the diff, so reproduced here:

    if (!kvm_arm_vcpu_sve_finalized(vcpu)) {
        if (test_bit(KVM_ARM_VCPU_SVE, vcpu->arch.features)) {
            ret = kvm_vcpu_enable_sve(vcpu);
            if (ret)
                goto out;
        }
    } else {
        kvm_vcpu_reset_sve(vcpu);
    }

 arch/arm64/kvm/reset.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/kvm/reset.c b/arch/arm64/kvm/reset.c
index d3b209023727..f1057603b756 100644
--- a/arch/arm64/kvm/reset.c
+++ b/arch/arm64/kvm/reset.c

@@ -245,7 +245,7 @@ static int kvm_vcpu_enable_ptrauth(struct kvm_vcpu

*vcpu)
  */
 int kvm_reset_vcpu(struct kvm_vcpu *vcpu)
 {
-    int ret = -EINVAL;
+    int ret;
     bool loaded;
     u32 pstate;

@@ -269,15 +269,19 @@ int kvm_reset_vcpu(struct kvm_vcpu *vcpu)

     if (test_bit(KVM_ARM_VCPU_PTRAUTH_ADDRESS, vcpu->arch.features) ||
         test_bit(KVM_ARM_VCPU_PTRAUTH_GENERIC, vcpu->arch.features)) {
-        if (kvm_vcpu_enable_ptrauth(vcpu))
+        if (kvm_vcpu_enable_ptrauth(vcpu)) {
+            ret = -EINVAL;
             goto out;
+        }
     }

     switch (vcpu->arch.target) {
     default:
         if (test_bit(KVM_ARM_VCPU_EL1_32BIT, vcpu->arch.features)) {
-            if (!cpus_have_const_cap(ARM64_HAS_32BIT_EL1))
+            if (cpus_have_const_cap(ARM64_HAS_32BIT_EL1)) {

Do you really mean this? Seems counter-productive... :-(

Clearly not... I'm really not sure how I managed to screw that up so 
badly :(

I'm glad someone is awake!

Sorry about that,

Steve

quoted

+                ret = -EINVAL;
                 goto out;
+            }
             pstate = VCPU_RESET_PSTATE_SVC;
         } else {
             pstate = VCPU_RESET_PSTATE_EL1;

Thanks,

         M.


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