Re: [PATCH v2 13/16] mempool: Use kmalloc_size_roundup() to match ksize() usage

Kees Cook
2022-09-26T18:26:26Z

On Mon, Sep 26, 2022 at 03:50:43PM +0200, Vlastimil Babka wrote:
> On 9/23/22 22:28, Kees Cook wrote:
> > Round up allocations with kmalloc_size_roundup() so that mempool's use
> > of ksize() is always accurate and no special handling of the memory is
> > needed by KASAN, UBSAN_BOUNDS, nor FORTIFY_SOURCE.
> >
> > Cc: Andrew Morton <akpm@linux-foundation.org>
> > Cc: linux-mm@kvack.org
> > Signed-off-by: Kees Cook <keescook@chromium.org>
> > ---
> > mm/mempool.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/mm/mempool.c b/mm/mempool.c
> > index 96488b13a1ef..0f3107b28e6b 100644
> > --- a/mm/mempool.c
> > +++ b/mm/mempool.c
> > @@ -526,7 +526,7 @@ EXPORT_SYMBOL(mempool_free_slab);
> > */
> > void *mempool_kmalloc(gfp_t gfp_mask, void *pool_data)
> > {
> > - size_t size = (size_t)pool_data;
> > + size_t size = kmalloc_size_roundup((size_t)pool_data);
>
> Hm it is kinda wasteful to call into kmalloc_size_roundup for every
> allocation that has the same input. We could do it just once in
> mempool_init_node() for adjusting pool->pool_data ?
>
> But looking more closely, I wonder why poison_element() and
> kasan_unpoison_element() in mm/mempool.c even have to use ksize()/__ksize()
> and not just operate on the requested size (again, pool->pool_data). If no
> kmalloc mempool's users use ksize() to write beyond requested size, then we
> don't have to unpoison/poison that area either?

Yeah, I think that's a fair point. I will adjust this.

--
Kees Cook