[PATCH v2 5/5] KVM: arm64: Simplify PtrAuth alternative patching
Marc Zyngier
maz at kernel.org
Mon Jun 22 06:25:41 EDT 2020
Hi Mark,
On 2020-06-22 10:15, Mark Rutland wrote:
> On Mon, Jun 22, 2020 at 09:06:43AM +0100, Marc Zyngier wrote:
>> We currently decide to execute the PtrAuth save/restore code based
>> on a set of branches that evaluate as (ARM64_HAS_ADDRESS_AUTH_ARCH ||
>> ARM64_HAS_ADDRESS_AUTH_IMP_DEF). This can be easily replaced by
>> a much simpler test as the ARM64_HAS_ADDRESS_AUTH capability is
>> exactly this expression.
>>
>> Suggested-by: Mark Rutland <mark.rutland at arm.com>
>> Signed-off-by: Marc Zyngier <maz at kernel.org>
>
> Looks good to me. One minor suggestion below, but either way:
>
> Acked-by: Mark Rutland <mark.rutland at arm.com>
>
>> ---
>> arch/arm64/include/asm/kvm_ptrauth.h | 26 +++++++++-----------------
>> 1 file changed, 9 insertions(+), 17 deletions(-)
>>
>> diff --git a/arch/arm64/include/asm/kvm_ptrauth.h
>> b/arch/arm64/include/asm/kvm_ptrauth.h
>> index f1830173fa9e..7a72508a841b 100644
>> --- a/arch/arm64/include/asm/kvm_ptrauth.h
>> +++ b/arch/arm64/include/asm/kvm_ptrauth.h
>> @@ -61,44 +61,36 @@
>>
>> /*
>> * Both ptrauth_switch_to_guest and ptrauth_switch_to_host macros
>> will
>> - * check for the presence of one of the cpufeature flag
>> - * ARM64_HAS_ADDRESS_AUTH_ARCH or ARM64_HAS_ADDRESS_AUTH_IMP_DEF and
>> + * check for the presence ARM64_HAS_ADDRESS_AUTH, which is defined as
>> + * (ARM64_HAS_ADDRESS_AUTH_ARCH || ARM64_HAS_ADDRESS_AUTH_IMP_DEF)
>> and
>> * then proceed ahead with the save/restore of Pointer Authentication
>> - * key registers.
>> + * key registers if enabled for the guest.
>> */
>> .macro ptrauth_switch_to_guest g_ctxt, reg1, reg2, reg3
>> -alternative_if ARM64_HAS_ADDRESS_AUTH_ARCH
>> +alternative_if_not ARM64_HAS_ADDRESS_AUTH
>> b 1000f
>> alternative_else_nop_endif
>> -alternative_if_not ARM64_HAS_ADDRESS_AUTH_IMP_DEF
>> - b 1001f
>> -alternative_else_nop_endif
>> -1000:
>> mrs \reg1, hcr_el2
>> and \reg1, \reg1, #(HCR_API | HCR_APK)
>> - cbz \reg1, 1001f
>> + cbz \reg1, 1000f
>> add \reg1, \g_ctxt, #CPU_APIAKEYLO_EL1
>> ptrauth_restore_state \reg1, \reg2, \reg3
>> -1001:
>> +1000:
>> .endm
>
> Since these are in macros, we could use \@ to generate a macro-specific
> lavel rather than a magic number, which would be less likely to
> conflict
> with the surrounding environment and would be more descriptive. We do
> that in a few places already, and here it could look something like:
>
> | alternative_if_not ARM64_HAS_ADDRESS_AUTH
> | b .L__skip_pauth_switch\@
> | alternative_else_nop_endif
> |
> | ...
> |
> | .L__skip_pauth_switch\@:
>
> Per the gas documentation
>
> | \@
> |
> | as maintains a counter of how many macros it has executed in this
> | pseudo-variable; you can copy that number to your output with
> ‘\@’,
> | but only within a macro definition.
>
> No worries if you don't want to change that now; the Acked-by stands
> either way.
I have folded in the following patch:
diff --git a/arch/arm64/include/asm/kvm_ptrauth.h
b/arch/arm64/include/asm/kvm_ptrauth.h
index 7a72508a841b..0ddf98c3ba9f 100644
--- a/arch/arm64/include/asm/kvm_ptrauth.h
+++ b/arch/arm64/include/asm/kvm_ptrauth.h
@@ -68,29 +68,29 @@
*/
.macro ptrauth_switch_to_guest g_ctxt, reg1, reg2, reg3
alternative_if_not ARM64_HAS_ADDRESS_AUTH
- b 1000f
+ b .L__skip_switch\@
alternative_else_nop_endif
mrs \reg1, hcr_el2
and \reg1, \reg1, #(HCR_API | HCR_APK)
- cbz \reg1, 1000f
+ cbz \reg1, .L__skip_switch\@
add \reg1, \g_ctxt, #CPU_APIAKEYLO_EL1
ptrauth_restore_state \reg1, \reg2, \reg3
-1000:
+.L__skip_switch\@:
.endm
.macro ptrauth_switch_to_host g_ctxt, h_ctxt, reg1, reg2, reg3
alternative_if_not ARM64_HAS_ADDRESS_AUTH
- b 2000f
+ b .L__skip_switch\@
alternative_else_nop_endif
mrs \reg1, hcr_el2
and \reg1, \reg1, #(HCR_API | HCR_APK)
- cbz \reg1, 2000f
+ cbz \reg1, .L__skip_switch\@
add \reg1, \g_ctxt, #CPU_APIAKEYLO_EL1
ptrauth_save_state \reg1, \reg2, \reg3
add \reg1, \h_ctxt, #CPU_APIAKEYLO_EL1
ptrauth_restore_state \reg1, \reg2, \reg3
isb
-2000:
+.L__skip_switch\@:
.endm
#else /* !CONFIG_ARM64_PTR_AUTH */
Thanks,
M.
--
Jazz is not dead. It just smells funny...
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