Re: [PATCH] riscv: Define TASK_SIZE_MAX for __access_ok()

[Arnd Bergmann]

On Wed, Mar 13, 2024, at 18:59, Samuel Holland wrote:
> TASK_SIZE_MAX should be set to the largest userspace address under any
> runtime configuration. This optimizes the check in __access_ok(), which
> no longer needs to compute the current value of TASK_SIZE. It is still
> safe because addresses between TASK_SIZE and TASK_SIZE_MAX are invalid
> at the hardware level.
>
> This removes about half of the references to pgtable_l[45]_enabled.
>
> Signed-off-by: Samuel Holland <samuel.holland@xxxxxxxxxx>

Reviewed-by: Arnd Bergmann <arnd@xxxxxxxx>

>  #ifdef CONFIG_64BIT
>  #define TASK_SIZE_64	(PGDIR_SIZE * PTRS_PER_PGD / 2)
>  #define TASK_SIZE_MIN	(PGDIR_SIZE_L3 * PTRS_PER_PGD / 2)
> +#define TASK_SIZE_MAX	(PGDIR_SIZE_L5 * PTRS_PER_PGD / 2)

I see that TASK_SIZE_MIN is unused since 085e2ff9aeb0 ("efi:
libstub: Drop randomization of runtime memory map") and could
be dropped now, but it doesn't really hurt either.

     Arnd