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KVM: nSVM: Check for NRIPS support before updating control field

PATCH Bandan Das 3 participants 4 messages Jun 29, 2015 – Jul 1, 2015

Subsystems (3)
Stable branch x86 KVM x86
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Bandan Das

author
#0 lore raw

Commit f104765b4f81fd74d69e0eb161e89096deade2db upstream.

This causes the L1 guest to crash when running a nested guest with an AMD processor that doesn't support NRIPS.

If hardware doesn't support DecodeAssist - a feature that provides more information about the intercept in the VMCB, KVM decodes the instruction and then updates the next_rip vmcb control field. However, NRIP support itself depends on cpuid Fn8000_000A_EDX[NRIPS]. Since skip_emulated_instruction() doesn't verify nrip support before accepting control.next_rip as valid, avoid writing this field if support isn't present.

Signed-off-by Bandan Das <[email protected]>
Signed-off-by Paolo Bonzini <[email protected]>
---
 arch/x86/kvm/svm.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)
arch/x86/kvm/svm.c +6 -2
index 6807531..e7685af 100644
@@ -511,8 +511,10 @@ static void skip_emulated_instruction(struct kvm_vcpu *vcpu)
 {
 	struct vcpu_svm *svm = to_svm(vcpu);
 
-	if (svm->vmcb->control.next_rip != 0)
+	if (svm->vmcb->control.next_rip != 0) {
+		WARN_ON(!static_cpu_has(X86_FEATURE_NRIPS));
 		svm->next_rip = svm->vmcb->control.next_rip;
+	}
 
 	if (!svm->next_rip) {
 		if (emulate_instruction(vcpu, EMULTYPE_SKIP) !=

@@ -4329,7 +4331,9 @@ static int svm_check_intercept(struct kvm_vcpu *vcpu,
 		break;
 	}
 
-	vmcb->control.next_rip  = info->next_rip;
+	/* TODO: Advertise NRIPS to guest hypervisor unconditionally */
+	if (static_cpu_has(X86_FEATURE_NRIPS))
+		vmcb->control.next_rip  = info->next_rip;
 	vmcb->control.exit_code = icpt_info.exit_code;
 	vmexit = nested_svm_exit_handled(svm);
Signature · 1 line
2.4.3
maintainer
#1 lore raw
Quoted 14 lines · Bandan Das

Commit f104765b4f81fd74d69e0eb161e89096deade2db upstream.

This causes the L1 guest to crash when running a nested guest with an AMD processor that doesn't support NRIPS.

If hardware doesn't support DecodeAssist - a feature that provides more information about the intercept in the VMCB, KVM decodes the instruction and then updates the next_rip vmcb control field. However, NRIP support itself depends on cpuid Fn8000_000A_EDX[NRIPS]. Since skip_emulated_instruction() doesn't verify nrip support before accepting control.next_rip as valid, avoid writing this field if support isn't present.

Quoted 5 lines
Signed-off-by Bandan Das <[email protected]>
Signed-off-by Paolo Bonzini <[email protected]>
---
 arch/x86/kvm/svm.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

What stable kernel trees do you want this applied to?

thanks,

greg k-h

author
#2 lore raw
Quoted 15 lines · Greg KH
Quoted 14 lines · Bandan Das

Commit f104765b4f81fd74d69e0eb161e89096deade2db upstream.

This causes the L1 guest to crash when running a nested guest with an AMD processor that doesn't support NRIPS.

If hardware doesn't support DecodeAssist - a feature that provides more information about the intercept in the VMCB, KVM decodes the instruction and then updates the next_rip vmcb control field. However, NRIP support itself depends on cpuid Fn8000_000A_EDX[NRIPS]. Since skip_emulated_instruction() doesn't verify nrip support before accepting control.next_rip as valid, avoid writing this field if support isn't present.

Quoted 7 lines
Quoted 5 lines
Signed-off-by Bandan Das <[email protected]>
Signed-off-by Paolo Bonzini <[email protected]>
---
 arch/x86/kvm/svm.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

What stable kernel trees do you want this applied to?

Sorry, I missed that part. I believe this bug is present since commit cfec82cb7d3 which makes it applicable to #3.0+

Bandan

Quoted 3 lines

thanks,

greg k-h

#3 lore raw
Quoted 23 lines · Bandan Das
Quoted 21 lines · Greg KH
Quoted 19 lines · Bandan Das

Commit f104765b4f81fd74d69e0eb161e89096deade2db upstream.

This causes the L1 guest to crash when running a nested guest with an AMD processor that doesn't support NRIPS.

If hardware doesn't support DecodeAssist - a feature that provides more information about the intercept in the VMCB, KVM decodes the instruction and then updates the next_rip vmcb control field. However, NRIP support itself depends on cpuid Fn8000_000A_EDX[NRIPS]. Since skip_emulated_instruction() doesn't verify nrip support before accepting control.next_rip as valid, avoid writing this field if support isn't present.

Signed-off-by Bandan Das <[email protected]>
Signed-off-by Paolo Bonzini <[email protected]>
---
 arch/x86/kvm/svm.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)
Quoted 6 lines
Quoted 1 line

What stable kernel trees do you want this applied to?

Sorry, I missed that part. I believe this bug is present since commit cfec82cb7d3 which makes it applicable to #3.0+

Thanks, queuing it for the 3.16 kernel.

Cheers,
--
Lu�s

Quoted 8 lines

Bandan

Quoted 3 lines

thanks,

greg k-h

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