Re: [PATCH 2/3] zram: do not use copy_page with non-page alinged address

Sergey Senozhatsky
2017-04-17T01:48:53Z

On (04/13/17 09:17), Minchan Kim wrote:
> The copy_page is optimized memcpy for page-alinged address.
> If it is used with non-page aligned address, it can corrupt memory which
> means system corruption. With zram, it can happen with
>
> 1. 64K architecture
> 2. partial IO
> 3. slub debug
>
> Partial IO need to allocate a page and zram allocates it via kmalloc.
> With slub debug, kmalloc(PAGE_SIZE) doesn't return page-size aligned
> address. And finally, copy_page(mem, cmem) corrupts memory.
>
> So, this patch changes it to memcpy.
>
> Acutaully, we don't need to change zram_bvec_write part because zsmalloc
> returns page-aligned address in case of PAGE_SIZE class but it's not
> good to rely on the internal of zsmalloc.
>
> Note:
> When this patch is merged to stable, clear_page should be fixed, too.
> Unfortunately, recent zram removes it by "same page merge" feature
> so it's hard to backport this patch to -stable tree.
>
> I will handle it when I receive the mail from stable tree maintainer
> to merge this patch to backport.
>
> Fixes: 42e99bd ("zram: optimize memory operations with clear_page()/copy_page()")
> Cc: stable@vger.kernel.org
> Signed-off-by: Minchan Kim <minchan@kernel.org>

Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>

-ss