Re: [Linaro-mm-sig] [PATCH v2 08/16] dma-buf: Proactively round up to kmalloc bucket size

Christian König
2022-09-26T09:30:55Z

Am 23.09.22 um 22:28 schrieb Kees Cook:
> Instead of discovering the kmalloc bucket size _after_ allocation, round
> up proactively so the allocation is explicitly made for the full size,
> allowing the compiler to correctly reason about the resulting size of
> the buffer through the existing __alloc_size() hint.
>
> Cc: Sumit Semwal <sumit.semwal@linaro.org>
> Cc: "Christian König" <christian.koenig@amd.com>
> Cc: linux-media@vger.kernel.org
> Cc: dri-devel@lists.freedesktop.org
> Cc: linaro-mm-sig@lists.linaro.org
> Signed-off-by: Kees Cook <keescook@chromium.org>

Reviewed-by: Christian König <christian.koenig@amd.com>

> ---
> drivers/dma-buf/dma-resv.c | 9 +++++++--
> 1 file changed, 7 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/dma-buf/dma-resv.c b/drivers/dma-buf/dma-resv.c
> index 205acb2c744d..5b0a4b8830ff 100644
> --- a/drivers/dma-buf/dma-resv.c
> +++ b/drivers/dma-buf/dma-resv.c
> @@ -98,12 +98,17 @@ static void dma_resv_list_set(struct dma_resv_list *list,
> static struct dma_resv_list *dma_resv_list_alloc(unsigned int max_fences)
> {
> struct dma_resv_list *list;
> + size_t size;
>
> - list = kmalloc(struct_size(list, table, max_fences), GFP_KERNEL);
> + /* Round up to the next kmalloc bucket size. */
> + size = kmalloc_size_roundup(struct_size(list, table, max_fences));
> +
> + list = kmalloc(size, GFP_KERNEL);
> if (!list)
> return NULL;
>
> - list->max_fences = (ksize(list) - offsetof(typeof(*list), table)) /
> + /* Given the resulting bucket size, recalculated max_fences. */
> + list->max_fences = (size - offsetof(typeof(*list), table)) /
> sizeof(*list->table);
>
> return list;