[PATCH v2 2/2] arm64: Do not configure kernel's PTR_AUTH key when it not needed.

[Will Deacon]

On Fri, Dec 18, 2020 at 12:56:32PM +0100, Daniel Kiss wrote:
> If the kernel is not compiled with CONFIG_ARM64_PTR_AUTH_KERNEL,
> then no need to install dedicated key for the kernel, user's key
> could be left enabled because no PACI/AUTI instructions are expected..

(same comment as before re commit message)

> Signed-off-by: Daniel Kiss <daniel.kiss at arm.com>
> ---
>  arch/arm64/include/asm/asm_pointer_auth.h | 53 +++++++++++++----------
>  arch/arm64/include/asm/pointer_auth.h     | 20 ++++++---
>  arch/arm64/include/asm/processor.h        |  2 +
>  arch/arm64/kernel/asm-offsets.c           |  4 ++
>  4 files changed, 51 insertions(+), 28 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/asm_pointer_auth.h b/arch/arm64/include/asm/asm_pointer_auth.h
> index 52dead2a8640..b2572a943f59 100644
> --- a/arch/arm64/include/asm/asm_pointer_auth.h
> +++ b/arch/arm64/include/asm/asm_pointer_auth.h
> @@ -39,27 +39,6 @@ alternative_if ARM64_HAS_GENERIC_AUTH
>  alternative_else_nop_endif
>  	.endm
>  
> -	.macro __ptrauth_keys_install_kernel_nosync tsk, tmp1, tmp2, tmp3
> -	mov	\tmp1, #THREAD_KEYS_KERNEL
> -	add	\tmp1, \tsk, \tmp1
> -	ldp	\tmp2, \tmp3, [\tmp1, #PTRAUTH_KERNEL_KEY_APIA]
> -	msr_s	SYS_APIAKEYLO_EL1, \tmp2
> -	msr_s	SYS_APIAKEYHI_EL1, \tmp3
> -	.endm
> -
> -	.macro ptrauth_keys_install_kernel_nosync tsk, tmp1, tmp2, tmp3
> -alternative_if ARM64_HAS_ADDRESS_AUTH
> -	__ptrauth_keys_install_kernel_nosync \tsk, \tmp1, \tmp2, \tmp3
> -alternative_else_nop_endif
> -	.endm
> -
> -	.macro ptrauth_keys_install_kernel tsk, tmp1, tmp2, tmp3
> -alternative_if ARM64_HAS_ADDRESS_AUTH
> -	__ptrauth_keys_install_kernel_nosync \tsk, \tmp1, \tmp2, \tmp3
> -	isb
> -alternative_else_nop_endif
> -	.endm
> -
>  	.macro __ptrauth_keys_init_cpu tsk, tmp1, tmp2, tmp3
>  	mrs	\tmp1, id_aa64isar1_el1
>  	ubfx	\tmp1, \tmp1, #ID_AA64ISAR1_APA_SHIFT, #8
> @@ -69,7 +48,9 @@ alternative_else_nop_endif
>  	mrs	\tmp2, sctlr_el1
>  	orr	\tmp2, \tmp2, \tmp1
>  	msr	sctlr_el1, \tmp2
> +#ifdef CONFIG_ARM64_PTR_AUTH_KERNEL
>  	__ptrauth_keys_install_kernel_nosync \tsk, \tmp1, \tmp2, \tmp3
> +#endif
>  	isb
>  .Lno_addr_auth\@:
>  	.endm
> @@ -82,17 +63,43 @@ alternative_else_nop_endif
>  .Lno_addr_auth\@:
>  	.endm
>  
> -#else /* CONFIG_ARM64_PTR_AUTH */
> +#else /* !CONFIG_ARM64_PTR_AUTH */
>  
>  	.macro ptrauth_keys_install_user tsk, tmp1, tmp2, tmp3
>  	.endm
>  
> +#endif /* CONFIG_ARM64_PTR_AUTH */
> +
> +#ifdef CONFIG_ARM64_PTR_AUTH_KERNEL
> +	.macro __ptrauth_keys_install_kernel_nosync tsk, tmp1, tmp2, tmp3
> +	mov	\tmp1, #THREAD_KEYS_KERNEL
> +	add	\tmp1, \tsk, \tmp1
> +	ldp	\tmp2, \tmp3, [\tmp1, #PTRAUTH_KERNEL_KEY_APIA]
> +	msr_s	SYS_APIAKEYLO_EL1, \tmp2
> +	msr_s	SYS_APIAKEYHI_EL1, \tmp3
> +	.endm
> +

nit: can you please define these macros at the top of the file, so that
they are defined before the macros which use them?

Will