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

[Amit Daniel Kachhap]

Hi,

On 2/21/19 9:23 PM, Dave Martin 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@xxxxxxx>
> > Cc: Mark Rutland <mark.rutland@xxxxxxx>
> > Cc: Marc Zyngier <marc.zyngier@xxxxxxx>
> > Cc: Christoffer Dall <christoffer.dall@xxxxxxx>
> > Cc: kvmarm@xxxxxxxxxxxxxxxxxxxxx
> > ---
> >   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/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> > index 1bacf78..2768a53 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)
> > @@ -451,6 +451,7 @@ static inline bool kvm_arch_requires_vhe(void)
> >   	return false;
> >   }
> >   
> > +bool kvm_arm_vcpu_ptrauth_allowed(const struct kvm_vcpu *vcpu);
> >   static inline bool kvm_supports_ptrauth(void)
> >   {
> >   	return has_vhe() && system_supports_address_auth() &&
>
> [...]
>
> > diff --git a/arch/arm64/kvm/hyp/ptrauth-sr.c b/arch/arm64/kvm/hyp/ptrauth-sr.c
> > index 528ee6e..6846a23 100644
> > --- a/arch/arm64/kvm/hyp/ptrauth-sr.c
> > +++ b/arch/arm64/kvm/hyp/ptrauth-sr.c
> > @@ -93,9 +93,23 @@ void kvm_arm_vcpu_ptrauth_reset(struct kvm_vcpu *vcpu)
>
> [...]
>
> > +/**
> > + * kvm_arm_vcpu_ptrauth_allowed - checks if ptrauth feature is allowed by user
> > + *
> > + * @vcpu: The VCPU pointer
> > + *
> > + * This function will be used to check userspace option to have ptrauth or not
> > + * in the guest kernel.
> > + */
> > +bool kvm_arm_vcpu_ptrauth_allowed(const struct kvm_vcpu *vcpu)
> > +{
> > +	return kvm_supports_ptrauth() &&
> > +		test_bit(KVM_ARM_VCPU_PTRAUTH, vcpu->arch.features);
> > +}
>
> Nit: for SVE is called the equivalent helper vcpu_has_sve(vcpu).
>
> Neither naming is more correct, but it would make sense to be
> consistent.  We will likely accumulate more of these vcpu feature
> predicates over time.
>
> Given that this is trivial and will be used all over the place, it
> probably makes sense to define it in kvm_host.h rather than having it
> out of line in a separate C file.
Ok I checked the SVE implementation. vcpu_has_ptrauth macro make more sense.
> > diff --git a/arch/arm64/kvm/reset.c b/arch/arm64/kvm/reset.c
> > index b72a3dd..987e0c3c 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 = kvm_supports_ptrauth();
> > +		break;
> >   	default:
> >   		r = 0;
> >   	}
> > diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
> > index 12529df..f7bcc60 100644
> > --- a/arch/arm64/kvm/sys_regs.c
> > +++ b/arch/arm64/kvm/sys_regs.c
> > @@ -1055,7 +1055,7 @@ static bool access_cntp_cval(struct kvm_vcpu *vcpu,
> >   }
> >   
> >   /* Read a sanitised cpufeature ID register by sys_reg_desc */
> > -static u64 read_id_reg(struct sys_reg_desc const *r, bool raz)
> > +static u64 read_id_reg(struct kvm_vcpu *vcpu, struct sys_reg_desc const *r, bool raz)
> >   {
> >   	u32 id = sys_reg((u32)r->Op0, (u32)r->Op1,
> >   			 (u32)r->CRn, (u32)r->CRm, (u32)r->Op2);
> > @@ -1071,7 +1071,7 @@ static u64 read_id_reg(struct sys_reg_desc const *r, bool raz)
> >   					 (0xfUL << ID_AA64ISAR1_API_SHIFT) |
> >   					 (0xfUL << ID_AA64ISAR1_GPA_SHIFT) |
> >   					 (0xfUL << ID_AA64ISAR1_GPI_SHIFT);
> > -		if (!kvm_supports_ptrauth()) {
> > +		if (!kvm_arm_vcpu_ptrauth_allowed(vcpu)) {
> >   			kvm_debug("ptrauth unsupported for guests, suppressing\n");
> >   			val &= ~ptrauth_mask;
> >   		}
> > @@ -1095,7 +1095,7 @@ static bool __access_id_reg(struct kvm_vcpu *vcpu,
> >   	if (p->is_write)
> >   		return write_to_read_only(vcpu, p, r);
> >   
> > -	p->regval = read_id_reg(r, raz);
> > +	p->regval = read_id_reg(vcpu, r, raz);
> >   	return true;
> >   }
>
> The SVE KVM series makes various overlapping changes to propagate vcpuo
> into the relevant places, but hopefully the rebase is not too painful.
> Many of the changes are probably virtually identical between the two
> series.
>
> See for example [1].  Maybe you could cherry-pick and drop the
> equivalent changes here (though if your series is picked up first, I
> will live with it ;)
Yes no issue. I will cherry-pick your specific patch and rebase mine on it.

Thanks,
Amit D
> [...]
>
> Cheers
> ---Dave
>
>
> [1] [PATCH v5 10/26] KVM: arm64: Propagate vcpu into read_id_reg()
> https://lists.cs.columbia.edu/pipermail/kvmarm/2019-February/034687.html