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

[Christian König]

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@xxxxxxxxxx>
> Cc: "Christian König" <christian.koenig@xxxxxxx>
> Cc: linux-media@xxxxxxxxxxxxxxx
> Cc: dri-devel@xxxxxxxxxxxxxxxxxxxxx
> Cc: linaro-mm-sig@xxxxxxxxxxxxxxxx
> Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>

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

> ---
>   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;