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SubjectRe: [PATCH v9 3/5] KVM: arm64: Add userspace flag to enable pointer authentication
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Hi,
On 4/16/19 10:01 PM, Dave Martin wrote:
> On Fri, Apr 12, 2019 at 08:50:34AM +0530, Amit Daniel Kachhap wrote:
>> 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.
>>
>> 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
>> ---
>>
>> Changes since v8:
>> * Update vcpu->arch.flags to final enable state. [Dave Martin]
>> * Change in Documentation to make clear the implementation of 2 vcpu
>> feature flags. [Dave Martin]
>>
>> Documentation/arm64/pointer-authentication.txt | 22 ++++++++++++++++++----
>> Documentation/virtual/kvm/api.txt | 6 ++++++
>> arch/arm64/include/asm/kvm_host.h | 2 +-
>> arch/arm64/include/uapi/asm/kvm.h | 2 ++
>> arch/arm64/kvm/reset.c | 24 ++++++++++++++++++++++++
>> 5 files changed, 51 insertions(+), 5 deletions(-)
>>
>> diff --git a/Documentation/arm64/pointer-authentication.txt b/Documentation/arm64/pointer-authentication.txt
>> index 5baca42..fc71b33 100644
>> --- a/Documentation/arm64/pointer-authentication.txt
>> +++ b/Documentation/arm64/pointer-authentication.txt
>> @@ -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.
>> diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt
>> index 68509de..9d202f4 100644
>> --- a/Documentation/virtual/kvm/api.txt
>> +++ b/Documentation/virtual/kvm/api.txt
>> @@ -2753,6 +2753,12 @@ 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.
>
> Nit: (arm64 only) would be less verbose.
ok.
>
>> + Must be requested if KVM_ARM_VCPU_PTRAUTH_GENERIC is also requested.
>> + - KVM_ARM_VCPU_PTRAUTH_GENERIC: Enables Generic Pointer authentication
>> + for the CPU and supported only on arm64 architecture.
>
> Ditto. (Not a big deal, though.)
>
>> + Must be requested if KVM_ARM_VCPU_PTRAUTH_ADDRESS is also requested.
>>
>> - KVM_ARM_VCPU_SVE: Enables SVE for the CPU (arm64 only).
>> Depends on KVM_CAP_ARM_SVE.
>> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
>> index a585d82..25f2598 100644
>> --- a/arch/arm64/include/asm/kvm_host.h
>> +++ b/arch/arm64/include/asm/kvm_host.h
>> @@ -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)
>> diff --git a/arch/arm64/include/uapi/asm/kvm.h b/arch/arm64/include/uapi/asm/kvm.h
>> index 6963b7e..fec2253 100644
>> --- a/arch/arm64/include/uapi/asm/kvm.h
>> +++ b/arch/arm64/include/uapi/asm/kvm.h
>> @@ -103,6 +103,8 @@ 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;
>> diff --git a/arch/arm64/kvm/reset.c b/arch/arm64/kvm/reset.c
>> index f13378d..d13406b 100644
>> --- a/arch/arm64/kvm/reset.c
>> +++ b/arch/arm64/kvm/reset.c
>> @@ -221,6 +221,24 @@ 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() || !system_supports_address_auth() ||
>> + !system_supports_generic_auth())
>> + return -EINVAL;
>
> Nit: Funny indentation. Please align with the "if (". It's also
> preferable to keep the two system_supports_xxx_auth() aligned or on the
> same line, since they go together. This might be clearer split up:
>
> if (!has_vhe())
> return -EINVAL;
>
> if (!system_supports_address_auth() ||
> !system_supports_generic_auth())
> return -EINVAL;
ok.
>
>> + /*
>
> I'd say "for now" here, since we might relax this rule later on.
>
>> + * 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 +279,12 @@ 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)) {
>
> Nit: funny indentation.
>
>> + if (kvm_vcpu_enable_ptrauth(vcpu))
>> + goto out;
>> + }
>> +
>
> [...]
>
> With those fixed,
sure.
>
> Reviewed-by: Dave Martin <Dave.Martin@arm.com>
Thanks,
Amit
>
> Cheers
> ---Dave
>

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