Re: [PATCH] selftests: secretmem: Floor the memory size to the multiple of page_size

[Mike Rapoport <rppt@kernel.org>]

On Thu, Dec 14, 2023 at 03:19:30PM +0500, Muhammad Usama Anjum wrote:
> The "locked-in-memory size" limit per process can be non-multiple of
> page_size. The mmap() fails if we try to allocate locked-in-memory
> with same size as the allowed limit if it isn't multiple of the
> page_size because mmap() rounds off the memory size to be allocated
> to next multiple of page_size.
> 
> Fix this by flooring the length to be allocated with mmap() to the
> previous multiple of the page_size.
> 
> Fixes: 76fe17ef588a ("secretmem: test: add basic selftest for memfd_secret(2)")
> Reported-by: "kernelci.org bot" <bot@kernelci.org>
> Signed-off-by: Muhammad Usama Anjum <usama.anjum@collabora.com>
> ---
>  tools/testing/selftests/mm/memfd_secret.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/tools/testing/selftests/mm/memfd_secret.c b/tools/testing/selftests/mm/memfd_secret.c
> index 957b9e18c729..9b298f6a04b3 100644
> --- a/tools/testing/selftests/mm/memfd_secret.c
> +++ b/tools/testing/selftests/mm/memfd_secret.c
> @@ -62,6 +62,9 @@ static void test_mlock_limit(int fd)
>  	char *mem;
>  
>  	len = mlock_limit_cur;
> +	if (len % page_size != 0)
> +		len = (len/page_size) * page_size;
> +

With mlock limit smaller than a page we get zero length here and mmap will
fail with -EINVAL because of it.
In this case I think we can just skip the first mmap and only check that
mmaping more than mlock limit fails.

>  	mem = mmap(NULL, len, prot, mode, fd, 0);
>  	if (mem == MAP_FAILED) {
>  		fail("unable to mmap secret memory\n");
> -- 
> 2.42.0
> 

-- 
Sincerely yours,
Mike.