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SubjectRe: [kvmtool PATCH v6 6/6] arm/kvm: arm64: Add a vcpu feature for pointer authentication
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Hi,

On 2/21/19 9:24 PM, Dave Martin wrote:
> On Tue, Feb 19, 2019 at 02:54:31PM +0530, Amit Daniel Kachhap wrote:
>> This is a runtime capabality for KVM tool to enable Armv8.3 Pointer
>> Authentication in guest kernel. A command line option --ptrauth is
>> required for this.
>>
>> Signed-off-by: Amit Daniel Kachhap <amit.kachhap@arm.com>
>> ---
>> arm/aarch32/include/kvm/kvm-cpu-arch.h | 1 +
>> arm/aarch64/include/asm/kvm.h | 1 +
>> arm/aarch64/include/kvm/kvm-config-arch.h | 4 +++-
>> arm/aarch64/include/kvm/kvm-cpu-arch.h | 1 +
>> arm/include/arm-common/kvm-config-arch.h | 1 +
>> arm/kvm-cpu.c | 6 ++++++
>> include/linux/kvm.h | 1 +
>> 7 files changed, 14 insertions(+), 1 deletion(-)
>>
>> diff --git a/arm/aarch32/include/kvm/kvm-cpu-arch.h b/arm/aarch32/include/kvm/kvm-cpu-arch.h
>> index d28ea67..520ea76 100644
>> --- a/arm/aarch32/include/kvm/kvm-cpu-arch.h
>> +++ b/arm/aarch32/include/kvm/kvm-cpu-arch.h
>> @@ -13,4 +13,5 @@
>> #define ARM_CPU_ID 0, 0, 0
>> #define ARM_CPU_ID_MPIDR 5
>>
>> +#define ARM_VCPU_PTRAUTH_FEATURE 0
>> #endif /* KVM__KVM_CPU_ARCH_H */
>> diff --git a/arm/aarch64/include/asm/kvm.h b/arm/aarch64/include/asm/kvm.h
>> index 97c3478..1068fd1 100644
>> --- a/arm/aarch64/include/asm/kvm.h
>> +++ b/arm/aarch64/include/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 /* CPU uses pointer authentication */
>>
>> struct kvm_vcpu_init {
>> __u32 target;
>> diff --git a/arm/aarch64/include/kvm/kvm-config-arch.h b/arm/aarch64/include/kvm/kvm-config-arch.h
>> index 04be43d..2074684 100644
>> --- a/arm/aarch64/include/kvm/kvm-config-arch.h
>> +++ b/arm/aarch64/include/kvm/kvm-config-arch.h
>> @@ -8,7 +8,9 @@
>> "Create PMUv3 device"), \
>> OPT_U64('\0', "kaslr-seed", &(cfg)->kaslr_seed, \
>> "Specify random seed for Kernel Address Space " \
>> - "Layout Randomization (KASLR)"),
>> + "Layout Randomization (KASLR)"), \
>> + OPT_BOOLEAN('\0', "ptrauth", &(cfg)->has_ptrauth, \
>> + "Enable address authentication"),
>
> Nit: doesn't this enable address *and* generic authentication? The
> discussion on what capababilities and enables the ABI exposes probably
> needs to conclude before we can finalise this here.
ok.
>
> However, I would recommend that we provide a single option here that
> turns both address authentication and generic authentication on, even
> if the ABI treats them independently. This is expected to be the common
> case by far.
ok
>
> We can always add more fine-grained options later if it turns out to be
> necessary.
Mark suggested to provide 2 flags [1] for Address and Generic
authentication so I was thinking of adding 2 features like,

+#define KVM_ARM_VCPU_PTRAUTH_ADDR 4 /* CPU uses pointer address
authentication */
+#define KVM_ARM_VCPU_PTRAUTH_GENERIC 5 /* CPU uses pointer generic
authentication */

And supply both of them concatenated in VCPU_INIT stage. Kernel KVM
would expect both feature requested together.

[1]: https://www.spinics.net/lists/arm-kernel/msg709181.html
>
>> #include "arm-common/kvm-config-arch.h"
>>
>> diff --git a/arm/aarch64/include/kvm/kvm-cpu-arch.h b/arm/aarch64/include/kvm/kvm-cpu-arch.h
>> index a9d8563..496ece8 100644
>> --- a/arm/aarch64/include/kvm/kvm-cpu-arch.h
>> +++ b/arm/aarch64/include/kvm/kvm-cpu-arch.h
>> @@ -17,4 +17,5 @@
>> #define ARM_CPU_CTRL 3, 0, 1, 0
>> #define ARM_CPU_CTRL_SCTLR_EL1 0
>>
>> +#define ARM_VCPU_PTRAUTH_FEATURE (1UL << KVM_ARM_VCPU_PTRAUTH)
>> #endif /* KVM__KVM_CPU_ARCH_H */
>> diff --git a/arm/include/arm-common/kvm-config-arch.h b/arm/include/arm-common/kvm-config-arch.h
>> index 5734c46..5badcbd 100644
>> --- a/arm/include/arm-common/kvm-config-arch.h
>> +++ b/arm/include/arm-common/kvm-config-arch.h
>> @@ -10,6 +10,7 @@ struct kvm_config_arch {
>> bool aarch32_guest;
>> bool has_pmuv3;
>> u64 kaslr_seed;
>> + bool has_ptrauth;
>> enum irqchip_type irqchip;
>> u64 fw_addr;
>> };
>> diff --git a/arm/kvm-cpu.c b/arm/kvm-cpu.c
>> index 7780251..4ac80f8 100644
>> --- a/arm/kvm-cpu.c
>> +++ b/arm/kvm-cpu.c
>> @@ -68,6 +68,12 @@ struct kvm_cpu *kvm_cpu__arch_init(struct kvm *kvm, unsigned long cpu_id)
>> vcpu_init.features[0] |= (1UL << KVM_ARM_VCPU_PSCI_0_2);
>> }
>>
>> + /* Set KVM_ARM_VCPU_PTRAUTH if available */
>> + if (kvm__supports_extension(kvm, KVM_CAP_ARM_PTRAUTH)) {
>> + if (kvm->cfg.arch.has_ptrauth)
>> + vcpu_init.features[0] |= ARM_VCPU_PTRAUTH_FEATURE;
>> + }
>> +
>
> I'm not too keen on requiring a dummy #define for AArch32 here. How do
> we handle other subarch-specific feature flags? Is there something we
> can reuse?
I will check it.

Thanks,
Amit D
>
> (For SVE I didn''t have a proper solution for this yet: my kvmtool
> patches are still a dirty hack...)
>
> [...]
>
> Cheers
> ---Dave
>

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