Subject: Re: [PATCH v4 2/7] powerpc/64: Add interrupt register sanitisation macros

From: "Nicholas Piggin" <[email-masked]>
Date: Tue, 29 Nov 2022 19:40:53 +1000

On Tue Nov 29, 2022 at 2:43 PM AEST, Rohan McLure wrote:
> Include in asm/ppc_asm.h macros to be used in multiple successive
> patches to implement zeroising architected registers in interrupt
> handlers. Registers will be sanitised in this fashion in future patches
> to reduce the speculation influence of user-controlled register values.
> These mitigations will be configurable through the
> CONFIG_INTERRUPT_SANITIZE_REGISTERS Kconfig option.
>
> Included are macros for conditionally zeroising registers and restoring
> as required with the mitigation enabled. With the mitigation disabled,
> non-volatiles must be restored on demand at separate locations to
> those required by the mitigation.
>
> Signed-off-by: Rohan McLure <[email-masked]>

Thanks. You might just call them SANITIZE_NVGPRS() etc if it's not
functionally important that they're zero. But I don't mind long names
too much.

Reviewed-by: Nicholas Piggin <[email-masked]>

> ---
> v4: New patch
> ---
>  arch/powerpc/include/asm/ppc_asm.h | 17 +++++++++++++++++
>  1 file changed, 17 insertions(+)
>
> diff --git a/arch/powerpc/include/asm/ppc_asm.h b/arch/powerpc/include/asm/ppc_asm.h
> index 753a2757bcd4..272b2795c36a 100644
> --- a/arch/powerpc/include/asm/ppc_asm.h
> +++ b/arch/powerpc/include/asm/ppc_asm.h
> @@ -74,6 +74,23 @@
>  #define SAVE_GPR(n, base)		SAVE_GPRS(n, n, base)
>  #define REST_GPR(n, base)		REST_GPRS(n, n, base)
>  
> +/* macros for handling user register sanitisation */
> +#ifdef CONFIG_INTERRUPT_SANITIZE_REGISTERS
> +#define SANITIZE_ZEROIZE_SYSCALL_GPRS()		ZEROIZE_GPR(0);		\
> +						ZEROIZE_GPRS(5, 12);	\
> +						ZEROIZE_NVGPRS()
> +#define SANITIZE_ZEROIZE_INTERRUPT_NVGPRS()	ZEROIZE_NVGPRS()
> +#define SANITIZE_ZEROIZE_NVGPRS()		ZEROIZE_NVGPRS()
> +#define SANITIZE_RESTORE_NVGPRS()		REST_NVGPRS(r1)
> +#define HANDLER_RESTORE_NVGPRS()
> +#else
> +#define SANITIZE_ZEROIZE_INTERRUPT_NVGPRS()
> +#define SANITIZE_ZEROIZE_SYSCALL_GPRS()
> +#define SANITIZE_ZEROIZE_NVGPRS()
> +#define SANITIZE_RESTORE_NVGPRS()
> +#define HANDLER_RESTORE_NVGPRS()		REST_NVGPRS(r1)
> +#endif /* CONFIG_INTERRUPT_SANITIZE_REGISTERS */
> +
>  #define SAVE_FPR(n, base)	stfd	n,8*TS_FPRWIDTH*(n)(base)
>  #define SAVE_2FPRS(n, base)	SAVE_FPR(n, base); SAVE_FPR(n+1, base)
>  #define SAVE_4FPRS(n, base)	SAVE_2FPRS(n, base); SAVE_2FPRS(n+2, base)
> -- 
> 2.37.2