Re: [PATCH REBASE v4 11/14] mips: Adjust brk randomization offset to fit generic version

[Alexandre Ghiti]

On 7/24/19 7:58 AM, 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>
> Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>
> ---
>   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..faa5aa615389 100644
> --- a/arch/mips/mm/mmap.c
> +++ b/arch/mips/mm/mmap.c
> @@ -16,6 +16,7 @@
>   #include <linux/random.h>
>   #include <linux/sched/signal.h>
>   #include <linux/sched/mm.h>
> +#include <linux/sizes.h>
>   
>   unsigned long shm_align_mask = PAGE_SIZE - 1;	/* Sane caches */
>   EXPORT_SYMBOL(shm_align_mask);
> @@ -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;
>   	else
> -		rnd = rnd & 0xffffffful;
> +		rnd = rnd & SZ_1G;
>   
>   	return rnd;
>   }

Hi Andrew,

I have just noticed that this patch is wrong, do you want me to send
another version of the entire series or is the following diff enough ?
This mistake gets fixed anyway in patch 13/14 when it gets merged with the
generic version.

Sorry about that,

Thanks,

Alex

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
@@ -16,6 +16,7 @@
Â#include <linux/random.h>
Â#include <linux/sched/signal.h>
Â#include <linux/sched/mm.h>
+#include <linux/sizes.h>

Âunsigned long shm_align_mask = PAGE_SIZE - 1;Â /* Sane caches */
ÂEXPORT_SYMBOL(shm_align_mask);
@@ -189,11 +190,11 @@ static inline unsigned long brk_rnd(void)
ÂÂÂÂÂÂÂ unsigned long rnd = get_random_long();

ÂÂÂÂÂÂÂ rnd = rnd << PAGE_SHIFT;
-ÂÂÂÂÂÂ /* 8MB for 32bit, 256MB for 64bit */
+ÂÂÂÂÂÂ /* 32MB for 32bit, 1GB for 64bit */
ÂÂÂÂÂÂÂ if (TASK_IS_32BIT_ADDR)
-ÂÂÂÂÂÂÂÂÂÂÂÂÂÂ rnd = rnd & 0x7ffffful;
+ÂÂÂÂÂÂÂÂÂÂÂÂÂÂ rnd = rnd & (SZ_32M - 1);
ÂÂÂÂÂÂÂ else
-ÂÂÂÂÂÂÂÂÂÂÂÂÂÂ rnd = rnd & 0xffffffful;
+ÂÂÂÂÂÂÂÂÂÂÂÂÂÂ rnd = rnd & (SZ_1G - 1);

ÂÂÂÂÂÂÂ return rnd;
Â}