Re: [PATCH v5 4/5] arm64/kvm: add a userspace option to enable pointer authentication

From: Amit Daniel Kachhap
Date: Thu Feb 14 2019 - 23:52:50 EST


On 2/13/19 11:05 PM, Kristina Martsenko wrote:
On 28/01/2019 06:58, Amit Daniel Kachhap wrote:
This feature will allow the KVM guest to allow the handling of
pointer authentication instructions or to treat them as undefined
if not set. It uses the existing vcpu API KVM_ARM_VCPU_INIT to
supply this parameter instead of creating a new API.

A new register is not created to pass this parameter via
SET/GET_ONE_REG interface as just a flag (KVM_ARM_VCPU_PTRAUTH)
supplied is enough to enable this feature.


diff --git a/arch/arm/include/asm/kvm_host.h b/arch/arm/include/asm/kvm_host.h
index b200c14..b6950df 100644
--- a/arch/arm/include/asm/kvm_host.h
+++ b/arch/arm/include/asm/kvm_host.h
@@ -346,6 +346,10 @@ static inline int kvm_arm_have_ssbd(void)
static inline void kvm_vcpu_load_sysregs(struct kvm_vcpu *vcpu) {}
static inline void kvm_vcpu_put_sysregs(struct kvm_vcpu *vcpu) {}
static inline void kvm_arm_vcpu_ptrauth_reset(struct kvm_vcpu *vcpu) {}
+static inline bool kvm_arm_vcpu_ptrauth_allowed(struct kvm_vcpu *vcpu)
+ return false;

It seems like this is only ever called from arm64 code, so do we need an
arch/arm/ definition?
Yes not required. Nice catch.

+ * kvm_arm_vcpu_ptrauth_allowed - checks if ptrauth feature is present in vcpu
+ *
+ * @vcpu: The VCPU pointer
+ *
+ * This function will be used to enable/disable ptrauth in guest as configured
+ * by the KVM userspace API.
+ */
+bool kvm_arm_vcpu_ptrauth_allowed(struct kvm_vcpu *vcpu)
+ return test_bit(KVM_ARM_VCPU_PTRAUTH, vcpu->arch.features);

I'm not sure, but should there also be something like

if (test_bit(KVM_ARM_VCPU_PTRAUTH, vcpu->arch.features) &&
return -EINVAL;

in kvm_reset_vcpu?
Yes makes sense. I missed it and with Dave martin patch this may be done cleanly.

Amit D