Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932444AbdDQBsD (ORCPT ); Sun, 16 Apr 2017 21:48:03 -0400 Received: from mail-pg0-f66.google.com ([74.125.83.66]:34981 "EHLO mail-pg0-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932128AbdDQBsA (ORCPT ); Sun, 16 Apr 2017 21:48:00 -0400 Date: Mon, 17 Apr 2017 10:48:03 +0900 From: Sergey Senozhatsky To: Minchan Kim , Christoph Lameter , Joonsoo Kim Cc: Andrew Morton , Michal Hocko , Vlastimil Babka , linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-team@lge.com, Sergey Senozhatsky , Sergey Senozhatsky Subject: copy_page() on a kmalloc-ed page with DEBUG_SLAB enabled (was "zram: do not use copy_page with non-page alinged address") Message-ID: <20170417014803.GC518@jagdpanzerIV.localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.8.1 (2017-04-11) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1614 Lines: 39 Hello, I'll fork it into a separate thread and Cc more MM people. sorry for top-posting. Minchan reported that doing copy_page() on a kmalloc(PAGE_SIZE) page with DEBUG_SLAB enabled can cause a memory corruption (See below or lkml.kernel.org/r/1492042622-12074-2-git-send-email-minchan@kernel.org ) that's an interesting problem. arm64 copy_page(), for instance, wants src and dst to be page aligned, which is reasonable, while generic copy_page(), on the contrary, simply does memcpy(). there are, probably, other callpaths that do copy_page() on kmalloc-ed pages and I'm wondering if there is some sort of a generic fix to the problem. > > 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. > > > > which would be the case for many other copy_page() calls in the kernel. > > right? if so - should the fix be in copy_page() then? > > I thought about it but was not sure it's good idea by several reasons > (but don't want to discuss it in this thread). > > Anyway, it's stable stuff so I don't want to make the patch bloat. > If you believe it is right direction and valuable, you could be > a volunteer. :) -ss