Commit a22fa321 authored by Amit Daniel Kachhap's avatar Amit Daniel Kachhap Committed by Marc Zyngier
Browse files

KVM: arm64: Add userspace flag to enable pointer authentication 



Now that the building blocks of pointer authentication are present, lets
add userspace flags KVM_ARM_VCPU_PTRAUTH_ADDRESS and
KVM_ARM_VCPU_PTRAUTH_GENERIC. These flags will enable pointer
authentication for the KVM guest on a per-vcpu basis through the ioctl
KVM_ARM_VCPU_INIT.

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

Necessary documentations are added to reflect the changes done.

Reviewed-by: default avatarDave Martin <Dave.Martin@arm.com>
Signed-off-by: default avatarAmit 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
Signed-off-by: default avatarMarc Zyngier <marc.zyngier@arm.com>
parent 384b40ca

Documentation/arm64/pointer-authentication.txt

+18 −4
Original line number Diff line number Diff line
@@ -87,7 +87,21 @@ 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 before enabling pointer authentication.

The separate userspace flag will allow to have no userspace ABI changes

if support is added in the future to allow these two features to be

enabled independently of one another.



As Arm Architecture specifies that Pointer Authentication feature is

implemented along with the VHE feature so KVM arm64 ptrauth code relies

on VHE mode to be present.



Additionally, when these vcpu feature flags are not set then KVM will

filter out the Pointer Authentication system key registers from

KVM_GET/SET_REG_* ioctls and mask those features from cpufeature ID

register. Any attempt to use the Pointer Authentication instructions will

result in an UNDEFINED exception being injected into the guest.

Documentation/virtual/kvm/api.txt

+10 −0
Original line number Diff line number Diff line
@@ -2761,6 +2761,16 @@ Possible features: 
	- 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 arm64 only.

	  Both KVM_ARM_VCPU_PTRAUTH_ADDRESS and KVM_ARM_VCPU_PTRAUTH_GENERIC

	  must be requested or neither must be requested.



	- KVM_ARM_VCPU_PTRAUTH_GENERIC: Enables Generic Pointer authentication

	  for arm64 only.

	  Both KVM_ARM_VCPU_PTRAUTH_ADDRESS and KVM_ARM_VCPU_PTRAUTH_GENERIC

	  must be requested or neither must be requested.



	- KVM_ARM_VCPU_SVE: Enables SVE for the CPU (arm64 only).

	  Depends on KVM_CAP_ARM_SVE.

	  Requires KVM_ARM_VCPU_FINALIZE(KVM_ARM_VCPU_SVE):

arch/arm64/include/asm/kvm_host.h

+1 −1
Original line number Diff line number Diff line
@@ -49,7 +49,7 @@ 


#define KVM_MAX_VCPUS VGIC_V3_MAX_CPUS



#define KVM_VCPU_MAX_FEATURES 5

#define KVM_VCPU_MAX_FEATURES 7



#define KVM_REQ_SLEEP \

	KVM_ARCH_REQ_FLAGS(0, KVM_REQUEST_WAIT | KVM_REQUEST_NO_WAKEUP)

arch/arm64/include/uapi/asm/kvm.h

+2 −0
Original line number Diff line number Diff line
@@ -104,6 +104,8 @@ struct kvm_regs { 
#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_SVE		4 /* enable SVE for this CPU */

#define KVM_ARM_VCPU_PTRAUTH_ADDRESS	5 /* VCPU uses address authentication */

#define KVM_ARM_VCPU_PTRAUTH_GENERIC	6 /* VCPU uses generic authentication */



struct kvm_vcpu_init {

	__u32 target;

arch/arm64/kvm/reset.c

+27 −0
Original line number Diff line number Diff line
@@ -221,6 +221,27 @@ static void kvm_vcpu_reset_sve(struct kvm_vcpu *vcpu) 
		memset(vcpu->arch.sve_state, 0, vcpu_sve_state_size(vcpu));

}



static int kvm_vcpu_enable_ptrauth(struct kvm_vcpu *vcpu)

{

	/* Support ptrauth only if the system supports these capabilities. */

	if (!has_vhe())

		return -EINVAL;



	if (!system_supports_address_auth() ||

	    !system_supports_generic_auth())

		return -EINVAL;

	/*

	 * For now make sure that both address/generic pointer authentication

	 * features are requested by the userspace together.

	 */

	if (!test_bit(KVM_ARM_VCPU_PTRAUTH_ADDRESS, vcpu->arch.features) ||

	    !test_bit(KVM_ARM_VCPU_PTRAUTH_GENERIC, vcpu->arch.features))

		return -EINVAL;



	vcpu->arch.flags |= KVM_ARM64_GUEST_HAS_PTRAUTH;

	return 0;

}



/**

 * kvm_reset_vcpu - sets core registers and sys_regs to reset value

 * @vcpu: The VCPU pointer
@@ -261,6 +282,12 @@ int kvm_reset_vcpu(struct kvm_vcpu *vcpu) 
		kvm_vcpu_reset_sve(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))

			goto out;

	}



	switch (vcpu->arch.target) {

	default:

		if (test_bit(KVM_ARM_VCPU_EL1_32BIT, vcpu->arch.features)) {

CRA Git | Maintained and supported by SUSTech CRA and CCSE