Re: [PATCH v5] mm/gup_test: safely calculate GUP batch size

["David Hildenbrand (Arm)" <david@kernel.org>]

On 9/15/26 12:25, Sarthak Sharma wrote:
> __gup_test_ioctl() calculates the end of a GUP batch using:
> 
> next = addr + nr * PAGE_SIZE;
> 
> If nr is too large, it can cause next to overflow and wrap around.
> If it wraps, the next > end check is bypassed and a large value
> of nr is passed to the GUP call, even though the pages array was
> allocated according to gup->size. This can lead to out of bounds writes.
> 
> Also, when fewer than PAGE_SIZE bytes remain, the calculated batch
> contains zero pages. The code still calls GUP functions with pages + i,
> which can point past the allocated array.
> 
> Calculate nr by taking the minimum of the number of pages per call and
> the pages remaining in the address range. Reject zero sized and non
> page aligned gup->size values and zero nr_pages_per_call value.
> 
> Fixes: 64c349f4ae78 ("mm: add infrastructure for get_user_pages_fast() benchmarking")
> Reviewed-by: Kiryl Shutsemau (Meta) <kas@kernel.org>
> Signed-off-by: Sarthak Sharma <sarthak.sharma@arm.com>
> ---

Acked-by: David Hildenbrand (Arm) <david@kernel.org>

-- 
Cheers,

David