Re: [PATCH v6 11/14] mips: Adjust brk randomization offset to fit generic version

[Sergei Shtylyov]

Hello!

On 08.08.2019 9:17, Alexandre Ghiti wrote:

> This commit simply bumps up to 32MB and 1GB the random offset
> of brk, compared to 8MB and 256MB, for 32bit and 64bit respectively.
>
> Suggested-by: Kees Cook <keescook@xxxxxxxxxxxx>
> Signed-off-by: Alexandre Ghiti <alex@xxxxxxxx>
> Acked-by: Paul Burton <paul.burton@xxxxxxxx>
> Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>
> Reviewed-by: Luis Chamberlain <mcgrof@xxxxxxxxxx>
> ---
>   arch/mips/mm/mmap.c | 7 ++++---
>   1 file changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/arch/mips/mm/mmap.c b/arch/mips/mm/mmap.c
> index a7e84b2e71d7..ff6ab87e9c56 100644
> --- a/arch/mips/mm/mmap.c
> +++ b/arch/mips/mm/mmap.c
[...]
> @@ -189,11 +190,11 @@ static inline unsigned long brk_rnd(void)
>   	unsigned long rnd = get_random_long();
>   
>   	rnd = rnd << PAGE_SHIFT;
> -	/* 8MB for 32bit, 256MB for 64bit */
> +	/* 32MB for 32bit, 1GB for 64bit */
>   	if (TASK_IS_32BIT_ADDR)
> -		rnd = rnd & 0x7ffffful;
> +		rnd = rnd & (SZ_32M - 1);
>   	else
> -		rnd = rnd & 0xffffffful;
> +		rnd = rnd & (SZ_1G - 1);

   Why not make these 'rnd &= SZ_* - 1', while at it anyways?

[...]

MBR, Sergei