Re: [PATCH v2] selftests/mm: Fix incorrect mmap() error handling with NULL instead of MAP_FAILED

[David Hildenbrand (Arm)]

On 5/13/26 11:56, Hongfu Li wrote:
> mmap() returns MAP_FAILED, which is defined as (void *)-1, on error,
> not NULL.  Several selftests incorrectly check the return value of
> mmap() using !ptr or ptr == NULL, which would erroneously treat
> MAP_FAILED as a valid pointer since MAP_FAILED is non-zero and
> non-NULL.  This can lead to segfaults when mmap() actually fails
> under memory pressure.

Well, your patch also adds more checks where we previously didn't have any checks?

> 
> Signed-off-by: Hongfu Li <lihongfu@xxxxxxxxxx>
> Reviewed-by: Dev Jain <dev.jain@xxxxxxx>
> ---
> v2:
> - Add missing mmap() return value checks in pkey_sighandler_tests.c
>   and protection_keys.c
> ---

[...]

> diff --git a/tools/testing/selftests/mm/protection_keys.c b/tools/testing/selftests/mm/protection_keys.c
> index 2085982dba69..580bf1668c71 100644
> --- a/tools/testing/selftests/mm/protection_keys.c
> +++ b/tools/testing/selftests/mm/protection_keys.c
> @@ -1217,6 +1217,7 @@ static void arch_force_pkey_reg_init(void)
>  	 * doing the XSAVE size enumeration dance.
>  	 */
>  	buf = mmap(NULL, 1*MB, PROT_READ|PROT_WRITE, MAP_ANONYMOUS|MAP_PRIVATE, -1, 0);
> +	pkey_assert(buf != (void *)-1);

What's the reason for not using MAP_FAILED?

-- 
Cheers,

David