Re: [PATCH v4 4/6] arm64/kvm: enable pointer authentication cpufeature conditionally

[James Morse]

Hi Amit,

On 18/12/2018 07:56, Amit Daniel Kachhap wrote:
> According to userspace settings, pointer authentication cpufeature
> is enabled/disabled from guests.

This reads like the guest is changing something in the host. Isn't this hiding
the id-register values from the guest?


> diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
> index 6af6c7d..ce6144a 100644
> --- a/arch/arm64/kvm/sys_regs.c
> +++ b/arch/arm64/kvm/sys_regs.c
> @@ -1066,6 +1066,15 @@ static u64 read_id_reg(struct sys_reg_desc const *r, bool raz)
>  			kvm_debug("SVE unsupported for guests, suppressing\n");
>  
>  		val &= ~(0xfUL << ID_AA64PFR0_SVE_SHIFT);
> +	} else if (id == SYS_ID_AA64ISAR1_EL1) {
> +		const u64 ptrauth_mask = (0xfUL << ID_AA64ISAR1_APA_SHIFT) |
> +					 (0xfUL << ID_AA64ISAR1_API_SHIFT) |
> +					 (0xfUL << ID_AA64ISAR1_GPA_SHIFT) |
> +					 (0xfUL << ID_AA64ISAR1_GPI_SHIFT);
> +		if (!kvm_arm_vcpu_ptrauth_allowed(vcpu)) {
> +			kvm_debug("ptrauth unsupported for guests, suppressing\n");
> +			val &= ~ptrauth_mask;
> +		}

I think this hunk should have been in the previous patch as otherwise its a
bisection oddity.

Could you merge this hunk with the previous patch, and move the mechanical bits
that pass vcpu around to a prior preparatory patch.

(I'm still unsure if we need to hide this as a user-controlled policy)


Thanks,

James