[v4,3/6] arm64/kvm: add a userspace option to enable pointer authentication
diff mbox series

Message ID 1545119810-12182-4-git-send-email-amit.kachhap@arm.com
State New
Headers show
Series
  • Add ARMv8.3 pointer authentication for kvm guest
Related show

Commit Message

Amit Kachhap Dec. 18, 2018, 7:56 a.m. UTC
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 select this feature.

Signed-off-by: Amit Daniel Kachhap <amit.kachhap@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Marc Zyngier <marc.zyngier@arm.com>
Cc: Christoffer Dall <christoffer.dall@arm.com>
Cc: kvmarm@lists.cs.columbia.edu
---
 Documentation/arm64/pointer-authentication.txt |  9 +++++----
 Documentation/virtual/kvm/api.txt              |  4 ++++
 arch/arm/include/asm/kvm_host.h                |  4 ++++
 arch/arm64/include/asm/kvm_host.h              |  7 ++++---
 arch/arm64/include/uapi/asm/kvm.h              |  1 +
 arch/arm64/kvm/handle_exit.c                   |  2 +-
 arch/arm64/kvm/hyp/ptrauth-sr.c                | 16 ++++++++++++++++
 arch/arm64/kvm/reset.c                         |  3 +++
 include/uapi/linux/kvm.h                       |  1 +
 9 files changed, 39 insertions(+), 8 deletions(-)

Comments

James Morse Jan. 4, 2019, 5:57 p.m. UTC | #1
Hi Amit,

On 18/12/2018 07:56, 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 select this feature.

What is the motivation for doing this? Doesn't ptrauth 'just' need turning on?
It doesn't need additional setup to be useable, or rely on some qemu support to
work properly. There isn't any hidden state that can't be migrated in the usual way.
Is it just because we don't want to commit to the ABI?


> diff --git a/Documentation/arm64/pointer-authentication.txt b/Documentation/arm64/pointer-authentication.txt
> index 5baca42..8c0f338 100644
> --- a/Documentation/arm64/pointer-authentication.txt
> +++ b/Documentation/arm64/pointer-authentication.txt
> @@ -87,7 +87,8 @@ 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 virtual machine is
> +created by passing a flag (KVM_ARM_VCPU_PTRAUTH) requesting this feature
> +to be enabled. Without this flag, pointer authentication is not enabled
> +in KVM guests and attempted use of the feature will result in an UNDEFINED
> +exception being injected into the guest.

> diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt
> index cd209f7..e20583a 100644
> --- a/Documentation/virtual/kvm/api.txt
> +++ b/Documentation/virtual/kvm/api.txt
> @@ -2634,6 +2634,10 @@ 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: Emulate Pointer authentication for the CPU.
> +	  Depends on KVM_CAP_ARM_PTRAUTH and only on arm64 architecture. If
> +	  set, then the KVM guest allows the execution of pointer authentication
> +	  instructions or treats them as undefined if not set.

> diff --git a/arch/arm64/kvm/hyp/ptrauth-sr.c b/arch/arm64/kvm/hyp/ptrauth-sr.c
> index 1bfaf74..03999bb 100644
> --- a/arch/arm64/kvm/hyp/ptrauth-sr.c
> +++ b/arch/arm64/kvm/hyp/ptrauth-sr.c
> @@ -71,3 +71,19 @@ void __hyp_text __ptrauth_switch_to_host(struct kvm_vcpu *vcpu,
>  	__ptrauth_save_state(guest_ctxt);
>  	__ptrauth_restore_state(host_ctxt);
>  }
> +
> +/**
> + * 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)
> +{
> +	if (test_bit(KVM_ARM_VCPU_PTRAUTH, vcpu->arch.features))
> +		return true;
> +	else
> +		return false;
> +}

Can't you return the result of test_bit() directly?


Thanks,

James
Amit Kachhap Jan. 9, 2019, 10:13 a.m. UTC | #2
Hi,

On Sat, Jan 5, 2019 at 12:05 AM James Morse <james.morse@arm.com> wrote:
>
> Hi Amit,
>
> On 18/12/2018 07:56, 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 select this feature.
>
> What is the motivation for doing this? Doesn't ptrauth 'just' need turning on?
> It doesn't need additional setup to be useable, or rely on some qemu support to
> work properly. There isn't any hidden state that can't be migrated in the usual way.
> Is it just because we don't want to commit to the ABI?
This allows migration of guest to non pointer authenticated supported
systems and hides the extra ptrauth registers.
Basically this suggestion was given by Christoffer
(https://lore.kernel.org/lkml/20180206123847.GY21802@cbox/).
 I don't have strong reservation to have this option and can be
dropped if this doesn't make sense.
>
>
> > diff --git a/Documentation/arm64/pointer-authentication.txt b/Documentation/arm64/pointer-authentication.txt
> > index 5baca42..8c0f338 100644
> > --- a/Documentation/arm64/pointer-authentication.txt
> > +++ b/Documentation/arm64/pointer-authentication.txt
> > @@ -87,7 +87,8 @@ 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 virtual machine is
> > +created by passing a flag (KVM_ARM_VCPU_PTRAUTH) requesting this feature
> > +to be enabled. Without this flag, pointer authentication is not enabled
> > +in KVM guests and attempted use of the feature will result in an UNDEFINED
> > +exception being injected into the guest.
>
> > diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt
> > index cd209f7..e20583a 100644
> > --- a/Documentation/virtual/kvm/api.txt
> > +++ b/Documentation/virtual/kvm/api.txt
> > @@ -2634,6 +2634,10 @@ 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: Emulate Pointer authentication for the CPU.
> > +       Depends on KVM_CAP_ARM_PTRAUTH and only on arm64 architecture. If
> > +       set, then the KVM guest allows the execution of pointer authentication
> > +       instructions or treats them as undefined if not set.
>
> > diff --git a/arch/arm64/kvm/hyp/ptrauth-sr.c b/arch/arm64/kvm/hyp/ptrauth-sr.c
> > index 1bfaf74..03999bb 100644
> > --- a/arch/arm64/kvm/hyp/ptrauth-sr.c
> > +++ b/arch/arm64/kvm/hyp/ptrauth-sr.c
> > @@ -71,3 +71,19 @@ void __hyp_text __ptrauth_switch_to_host(struct kvm_vcpu *vcpu,
> >       __ptrauth_save_state(guest_ctxt);
> >       __ptrauth_restore_state(host_ctxt);
> >  }
> > +
> > +/**
> > + * 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)
> > +{
> > +     if (test_bit(KVM_ARM_VCPU_PTRAUTH, vcpu->arch.features))
> > +             return true;
> > +     else
> > +             return false;
> > +}
>
> Can't you return the result of test_bit() directly?
ok.
>
>
> Thanks,
>
> James

//Amit
James Morse Jan. 31, 2019, 4:19 p.m. UTC | #3
Hi Amit,

On 09/01/2019 10:13, Amit Daniel Kachhap wrote:
> On Sat, Jan 5, 2019 at 12:05 AM James Morse <james.morse@arm.com> wrote:
>> On 18/12/2018 07:56, 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 select this feature.
>>
>> What is the motivation for doing this? Doesn't ptrauth 'just' need turning on?
>> It doesn't need additional setup to be useable, or rely on some qemu support to
>> work properly. There isn't any hidden state that can't be migrated in the usual way.
>> Is it just because we don't want to commit to the ABI?

> This allows migration of guest to non pointer authenticated supported
> systems and hides the extra ptrauth registers.

The MIDR already has to match, so the hardware must be the same. I guess this
lets us hide the new feature so old-guests can migrate to a new-kernel without a
write to the id registers failing.


> Basically this suggestion was given by Christoffer
> (https://lore.kernel.org/lkml/20180206123847.GY21802@cbox/).

Ah, Christoffer asked for it, that's reason enough!


Thanks,

James

Patch
diff mbox series

diff --git a/Documentation/arm64/pointer-authentication.txt b/Documentation/arm64/pointer-authentication.txt
index 5baca42..8c0f338 100644
--- a/Documentation/arm64/pointer-authentication.txt
+++ b/Documentation/arm64/pointer-authentication.txt
@@ -87,7 +87,8 @@  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 virtual machine is
+created by passing a flag (KVM_ARM_VCPU_PTRAUTH) requesting this feature
+to be enabled. Without this flag, pointer authentication is not enabled
+in KVM guests and attempted use of the feature will result in an UNDEFINED
+exception being injected into the guest.
diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt
index cd209f7..e20583a 100644
--- a/Documentation/virtual/kvm/api.txt
+++ b/Documentation/virtual/kvm/api.txt
@@ -2634,6 +2634,10 @@  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: Emulate Pointer authentication for the CPU.
+	  Depends on KVM_CAP_ARM_PTRAUTH and only on arm64 architecture. If
+	  set, then the KVM guest allows the execution of pointer authentication
+	  instructions or treats them as undefined if not set.
 
 
 4.83 KVM_ARM_PREFERRED_TARGET
diff --git a/arch/arm/include/asm/kvm_host.h b/arch/arm/include/asm/kvm_host.h
index 02d9bfc..62a85d9 100644
--- a/arch/arm/include/asm/kvm_host.h
+++ b/arch/arm/include/asm/kvm_host.h
@@ -352,6 +352,10 @@  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_config(struct kvm_vcpu *vcpu) {}
+static inline bool kvm_arm_vcpu_ptrauth_allowed(struct kvm_vcpu *vcpu)
+{
+	return false;
+}
 
 #define __KVM_HAVE_ARCH_VM_ALLOC
 struct kvm *kvm_arch_alloc_vm(void);
diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
index 629712d..f853a95 100644
--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h
@@ -43,7 +43,7 @@ 
 
 #define KVM_MAX_VCPUS VGIC_V3_MAX_CPUS
 
-#define KVM_VCPU_MAX_FEATURES 4
+#define KVM_VCPU_MAX_FEATURES 5
 
 #define KVM_REQ_SLEEP \
 	KVM_ARCH_REQ_FLAGS(0, KVM_REQUEST_WAIT | KVM_REQUEST_NO_WAKEUP)
@@ -453,14 +453,15 @@  static inline bool kvm_arch_check_sve_has_vhe(void)
 
 void kvm_arm_vcpu_ptrauth_enable(struct kvm_vcpu *vcpu);
 void kvm_arm_vcpu_ptrauth_disable(struct kvm_vcpu *vcpu);
+bool kvm_arm_vcpu_ptrauth_allowed(struct kvm_vcpu *vcpu);
 
 static inline void kvm_arm_vcpu_ptrauth_config(struct kvm_vcpu *vcpu)
 {
 	/* Disable ptrauth and use it in a lazy context via traps */
-	if (has_vhe() && system_supports_ptrauth())
+	if (has_vhe() && system_supports_ptrauth()
+			&& kvm_arm_vcpu_ptrauth_allowed(vcpu))
 		kvm_arm_vcpu_ptrauth_disable(vcpu);
 }
-
 void kvm_arm_vcpu_ptrauth_trap(struct kvm_vcpu *vcpu);
 
 static inline void kvm_arch_hardware_unsetup(void) {}
diff --git a/arch/arm64/include/uapi/asm/kvm.h b/arch/arm64/include/uapi/asm/kvm.h
index 97c3478..5f82ca1 100644
--- a/arch/arm64/include/uapi/asm/kvm.h
+++ b/arch/arm64/include/uapi/asm/kvm.h
@@ -102,6 +102,7 @@  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		4 /* VCPU uses address authentication */
 
 struct kvm_vcpu_init {
 	__u32 target;
diff --git a/arch/arm64/kvm/handle_exit.c b/arch/arm64/kvm/handle_exit.c
index 5c47a8f47..3394028 100644
--- a/arch/arm64/kvm/handle_exit.c
+++ b/arch/arm64/kvm/handle_exit.c
@@ -180,7 +180,7 @@  static int handle_sve(struct kvm_vcpu *vcpu, struct kvm_run *run)
  */
 void kvm_arm_vcpu_ptrauth_trap(struct kvm_vcpu *vcpu)
 {
-	if (system_supports_ptrauth())
+	if (system_supports_ptrauth() && kvm_arm_vcpu_ptrauth_allowed(vcpu))
 		kvm_arm_vcpu_ptrauth_enable(vcpu);
 	else
 		kvm_inject_undefined(vcpu);
diff --git a/arch/arm64/kvm/hyp/ptrauth-sr.c b/arch/arm64/kvm/hyp/ptrauth-sr.c
index 1bfaf74..03999bb 100644
--- a/arch/arm64/kvm/hyp/ptrauth-sr.c
+++ b/arch/arm64/kvm/hyp/ptrauth-sr.c
@@ -71,3 +71,19 @@  void __hyp_text __ptrauth_switch_to_host(struct kvm_vcpu *vcpu,
 	__ptrauth_save_state(guest_ctxt);
 	__ptrauth_restore_state(host_ctxt);
 }
+
+/**
+ * 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)
+{
+	if (test_bit(KVM_ARM_VCPU_PTRAUTH, vcpu->arch.features))
+		return true;
+	else
+		return false;
+}
diff --git a/arch/arm64/kvm/reset.c b/arch/arm64/kvm/reset.c
index b72a3dd..4656070 100644
--- a/arch/arm64/kvm/reset.c
+++ b/arch/arm64/kvm/reset.c
@@ -91,6 +91,9 @@  int kvm_arch_vm_ioctl_check_extension(struct kvm *kvm, long ext)
 	case KVM_CAP_ARM_VM_IPA_SIZE:
 		r = kvm_ipa_limit;
 		break;
+	case KVM_CAP_ARM_PTRAUTH:
+		r = system_supports_ptrauth();
+		break;
 	default:
 		r = 0;
 	}
diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index 2b7a652..fa48660 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -975,6 +975,7 @@  struct kvm_ppc_resize_hpt {
 #define KVM_CAP_HYPERV_ENLIGHTENED_VMCS 163
 #define KVM_CAP_EXCEPTION_PAYLOAD 164
 #define KVM_CAP_ARM_VM_IPA_SIZE 165
+#define KVM_CAP_ARM_PTRAUTH 166
 
 #ifdef KVM_CAP_IRQ_ROUTING