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

On 2020-06-15 11:03, Mark Rutland wrote:

On Mon, Jun 15, 2020 at 09:19:51AM +0100, Marc Zyngier wrote:

quoted

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.

Ah, fair enough.

quoted

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.

That'd be a nice cleanup, as the two back to back alternatives are a bit 
hard to read.

quoted

+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.

Looks like this code isn't in -rc1 anymore, replaced with a mov_q in 
__ptrauth_keys_init_cpu.

I'll switch to that in v2.

Thanks,

         M.
-- 
Jazz is not dead. It just smells funny...

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