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SubjectRe: [PATCH v6 4/6] arm64/kvm: add a userspace option to enable pointer authentication
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Hi,

On 2/21/19 6:04 PM, Mark Rutland wrote:
> On Tue, Feb 19, 2019 at 02:54:29PM +0530, 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.
>>
>> 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/arm64/include/asm/kvm_host.h | 3 ++-
>> 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 +++
>> arch/arm64/kvm/sys_regs.c | 26 +++++++++++++-------------
>> include/uapi/linux/kvm.h | 1 +
>> 9 files changed, 45 insertions(+), 20 deletions(-)
>>
>> diff --git a/Documentation/arm64/pointer-authentication.txt b/Documentation/arm64/pointer-authentication.txt
>> index a25cd21..0529a7d 100644
>> --- a/Documentation/arm64/pointer-authentication.txt
>> +++ b/Documentation/arm64/pointer-authentication.txt
>> @@ -82,7 +82,8 @@ pointers).
>> 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 356156f..1e646fb 100644
>> --- a/Documentation/virtual/kvm/api.txt
>> +++ b/Documentation/virtual/kvm/api.txt
>> @@ -2642,6 +2642,10 @@ 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. Otherwise, KVM treats these instructions as undefined.
>
> I think that we should have separate flags for address auth and generic
> auth, to match the ID register split.
>
> For now, we can have KVM only support the case where both are set, but
> it gives us freedom to support either in isolation if we have to in
> future, without an ABI break.
yes agree with you about having two address and generic ptrauth flags.
Will add in next iteration.

Thanks,
Amit D
>
> Thanks,
> Mark.
>

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