Re: [PATCH 1/4] KVM: arm64: Enable Pointer Authentication at EL2 if available

Mark Rutland
2020-06-15T10:03:28Z

On Mon, Jun 15, 2020 at 09:19:51AM +0100, Marc Zyngier wrote:
> While initializing EL2, switch Pointer Authentication if detected
> from EL1. We use the EL1-provided keys though.

Perhaps "enable address authentication", to avoid confusion with
context-switch, and since generic authentication cannot be disabled
locally at EL2.

>
> Signed-off-by: Marc Zyngier <maz@kernel.org>
> ---
> arch/arm64/kvm/hyp-init.S | 11 +++++++++++
> 1 file changed, 11 insertions(+)
>
> diff --git a/arch/arm64/kvm/hyp-init.S b/arch/arm64/kvm/hyp-init.S
> index 6e6ed5581eed..81732177507d 100644
> --- a/arch/arm64/kvm/hyp-init.S
> +++ b/arch/arm64/kvm/hyp-init.S
> @@ -104,6 +104,17 @@ alternative_else_nop_endif
> */
> mov_q x4, (SCTLR_EL2_RES1 | (SCTLR_ELx_FLAGS & ~SCTLR_ELx_A))
> CPU_BE( orr x4, x4, #SCTLR_ELx_EE)
> +alternative_if ARM64_HAS_ADDRESS_AUTH_ARCH
> + b 1f
> +alternative_else_nop_endif
> +alternative_if_not ARM64_HAS_ADDRESS_AUTH_IMP_DEF
> + b 2f
> +alternative_else_nop_endif

I see this is the same pattern we use in the kvm context switch, but I
think we can use the ARM64_HAS_ADDRESS_AUTH cap instead (likewise in the
existing code).

AFAICT that won't permit mismatch given both ARM64_HAS_ADDRESS_AUTH_ARCH
and ARM64_HAS_ADDRESS_AUTH_IMP_DEF are dealt with as
ARM64_CPUCAP_BOOT_CPU_FEATURE.

> +1:
> + orr x4, x4, #(SCTLR_ELx_ENIA | SCTLR_ELx_ENIB)
> + orr x4, x4, #SCTLR_ELx_ENDA
> + orr x4, x4, #SCTLR_ELx_ENDB

Assuming we have a spare register, it would be nice if we could follow the same
pattern as in proc.S, where we do:

| ldr x2, =SCTLR_ELx_ENIA | SCTLR_ELx_ENIB | \
| SCTLR_ELx_ENDA | SCTLR_ELx_ENDB
| orr x0, x0, x2

... though we could/should use mov_q rather than a load literal, here and in
proc.S.

... otherwise this looks sound to me.

Thanks,
Mark.

> +2:
> msr sctlr_el2, x4
> isb
>
> --
> 2.27.0
>
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