Subject: Re: pkeys: Reserve PKEY_DISABLE_READ

From: Florian Weimer <[email-masked]>
Date: Tue, 27 Nov 2018 12:57:15 +0100

* Ram Pai:

> diff --git a/arch/x86/include/uapi/asm/mman.h b/arch/x86/include/uapi/asm/mman.h
> index d4a8d04..e9b121b 100644
> --- a/arch/x86/include/uapi/asm/mman.h
> +++ b/arch/x86/include/uapi/asm/mman.h
> @@ -24,6 +24,11 @@
>  		((key) & 0x2 ? VM_PKEY_BIT1 : 0) |      \
>  		((key) & 0x4 ? VM_PKEY_BIT2 : 0) |      \
>  		((key) & 0x8 ? VM_PKEY_BIT3 : 0))
> +
> +/* Override any generic PKEY permission defines */
> +#undef PKEY_ACCESS_MASK
> +#define PKEY_ACCESS_MASK       (PKEY_DISABLE_ACCESS |\
> +				PKEY_DISABLE_WRITE)
>  #endif

I would have expected something that translates PKEY_DISABLE_WRITE |
PKEY_DISABLE_READ into PKEY_DISABLE_ACCESS, and also accepts
PKEY_DISABLE_ACCESS | PKEY_DISABLE_READ, for consistency with POWER.

(My understanding is that PKEY_DISABLE_ACCESS does not disable all
access, but produces execute-only memory.)

> diff --git a/include/uapi/asm-generic/mman-common.h b/include/uapi/asm-generic/mman-common.h
> index e7ee328..61168e4 100644
> --- a/include/uapi/asm-generic/mman-common.h
> +++ b/include/uapi/asm-generic/mman-common.h
> @@ -71,7 +71,8 @@
>  
>  #define PKEY_DISABLE_ACCESS	0x1
>  #define PKEY_DISABLE_WRITE	0x2
> -#define PKEY_ACCESS_MASK	(PKEY_DISABLE_ACCESS |\
> -				 PKEY_DISABLE_WRITE)
> -
> +#define PKEY_DISABLE_EXECUTE	0x4
> +#define PKEY_DISABLE_READ	0x8
> +#define PKEY_ACCESS_MASK	0x0	/* arch can override and define its own
> +					   mask bits */
>  #endif /* __ASM_GENERIC_MMAN_COMMON_H */

I think Dave requested a value for PKEY_DISABLE_READ which is further
away from the existing bits.

Thanks,
Florian