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

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Date:   Mon, 17 Apr 2017 10:48:53 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:     Minchan Kim <minchan@...nel.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        kernel-team@....com, stable@...r.kernel.org
Subject: Re: [PATCH 2/3] zram: do not use copy_page with non-page alinged
 address

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@...r.kernel.org
> Signed-off-by: Minchan Kim <minchan@...nel.org>

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

	-ss