[PATCH v8 6/9] KVM: arm64: Add vcpu feature flags to control ptrauth accessibility

[Amit Daniel Kachhap]

Since Pointer authentication will be enabled or disabled on a
per-vcpu basis, vcpu feature flags are added in order to know which
vcpus have it enabled from userspace.

This features will allow the KVM guest to allow the handling of
pointer authentication instructions or to treat them as undefined
if not set.

The helper macro added checks the feature flag along with other
conditions such as VHE mode present and system support for
pointer address/generic authentication.

Necessary documentations are added to reflect the changes done.

Signed-off-by: Amit Daniel Kachhap <amit.kachhap@xxxxxxx>
Cc: Mark Rutland <mark.rutland@xxxxxxx>
Cc: Marc Zyngier <marc.zyngier@xxxxxxx>
Cc: Christoffer Dall <christoffer.dall@xxxxxxx>
Cc: kvmarm@xxxxxxxxxxxxxxxxxxxxx
---

Changes since v7:
* Moved the check for userspace features in this patch [James Morse].
* Moved the vcpu feature flags Documentation in this patch [James Morse].

 Documentation/arm64/pointer-authentication.txt | 13 +++++++++----
 Documentation/virtual/kvm/api.txt              |  4 ++++
 arch/arm64/include/asm/kvm_host.h              |  8 +++++++-
 arch/arm64/include/uapi/asm/kvm.h              |  2 ++
 arch/arm64/kvm/reset.c                         |  7 +++++++
 5 files changed, 29 insertions(+), 5 deletions(-)

diff --git a/Documentation/arm64/pointer-authentication.txt b/Documentation/arm64/pointer-authentication.txt
index 5baca42..b164886 100644
--- a/Documentation/arm64/pointer-authentication.txt
+++ b/Documentation/arm64/pointer-authentication.txt
@@ -87,7 +87,12 @@ used to get and set the keys for a thread.
 Virtualization
 --------------
 
-Pointer authentication is not currently supported in KVM guests. KVM
-will mask the feature bits from ID_AA64ISAR1_EL1, and attempted use of
-the feature will result in an UNDEFINED exception being injected into
-the guest.
+Pointer authentication is enabled in KVM guest when each virtual cpu is
+initialised by passing flags KVM_ARM_VCPU_PTRAUTH_[ADDRESS/GENERIC] and
+requesting these two separate cpu features to be enabled. The current KVM
+guest implementation works by enabling both features together, so both these
+userspace flags are checked together before enabling pointer authentication.
+The separate userspace flag will allow to have no userspace ABI changes when
+both features are implemented in an isolated way in future.
+
+Pointer Authentication is supported in KVM guest only in VHE mode.
diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt
index 7de9eee..aaa048d 100644
--- a/Documentation/virtual/kvm/api.txt
+++ b/Documentation/virtual/kvm/api.txt
@@ -2659,6 +2659,10 @@ Possible features:
 	  Depends on KVM_CAP_ARM_PSCI_0_2.
 	- KVM_ARM_VCPU_PMU_V3: Emulate PMUv3 for the CPU.
 	  Depends on KVM_CAP_ARM_PMU_V3.
+	- KVM_ARM_VCPU_PTRAUTH_ADDRESS: Enables Address Pointer authentication
+	  for the CPU and supported only on arm64 architecture.
+	- KVM_ARM_VCPU_PTRAUTH_GENERIC: Enables Generic Pointer authentication
+	  for the CPU and supported only on arm64 architecture.
 
 
 4.83 KVM_ARM_PREFERRED_TARGET
diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
index e3ccd7b..9dd2918 100644
--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h
@@ -45,7 +45,7 @@
 
 #define KVM_MAX_VCPUS VGIC_V3_MAX_CPUS
 
-#define KVM_VCPU_MAX_FEATURES 4
+#define KVM_VCPU_MAX_FEATURES 6
 
 #define KVM_REQ_SLEEP \
 	KVM_ARCH_REQ_FLAGS(0, KVM_REQUEST_WAIT | KVM_REQUEST_NO_WAKEUP)
@@ -491,6 +491,12 @@ static inline bool kvm_arch_requires_vhe(void)
 	return false;
 }
 
+#define vcpu_has_ptrauth(vcpu)	(has_vhe() && \
+		system_supports_address_auth() && \
+		system_supports_generic_auth() && \
+		test_bit(KVM_ARM_VCPU_PTRAUTH_ADDRESS, vcpu->arch.features) && \
+		test_bit(KVM_ARM_VCPU_PTRAUTH_GENERIC, vcpu->arch.features))
+
 static inline void kvm_arch_hardware_unsetup(void) {}
 static inline void kvm_arch_sync_events(struct kvm *kvm) {}
 static inline void kvm_arch_vcpu_uninit(struct kvm_vcpu *vcpu) {}
diff --git a/arch/arm64/include/uapi/asm/kvm.h b/arch/arm64/include/uapi/asm/kvm.h
index 97c3478..8806f71 100644
--- a/arch/arm64/include/uapi/asm/kvm.h
+++ b/arch/arm64/include/uapi/asm/kvm.h
@@ -102,6 +102,8 @@ struct kvm_regs {
 #define KVM_ARM_VCPU_EL1_32BIT		1 /* CPU running a 32bit VM */
 #define KVM_ARM_VCPU_PSCI_0_2		2 /* CPU uses PSCI v0.2 */
 #define KVM_ARM_VCPU_PMU_V3		3 /* Support guest PMUv3 */
+#define KVM_ARM_VCPU_PTRAUTH_ADDRESS	4 /* VCPU uses address authentication */
+#define KVM_ARM_VCPU_PTRAUTH_GENERIC	5 /* VCPU uses generic authentication */
 
 struct kvm_vcpu_init {
 	__u32 target;
diff --git a/arch/arm64/kvm/reset.c b/arch/arm64/kvm/reset.c
index f16a5f8..717afed 100644
--- a/arch/arm64/kvm/reset.c
+++ b/arch/arm64/kvm/reset.c
@@ -128,6 +128,13 @@ int kvm_reset_vcpu(struct kvm_vcpu *vcpu)
 	if (loaded)
 		kvm_arch_vcpu_put(vcpu);
 
+	if (test_bit(KVM_ARM_VCPU_PTRAUTH_ADDRESS, vcpu->arch.features) ||
+		test_bit(KVM_ARM_VCPU_PTRAUTH_GENERIC, vcpu->arch.features)) {
+		/* Verify that KVM startup matches the conditions for ptrauth */
+		if (!vcpu_has_ptrauth(vcpu))
+			goto out;
+	}
+
 	switch (vcpu->arch.target) {
 	default:
 		if (test_bit(KVM_ARM_VCPU_EL1_32BIT, vcpu->arch.features)) {
-- 
2.7.4