From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf0-f197.google.com (mail-pf0-f197.google.com [209.85.192.197]) by kanga.kvack.org (Postfix) with ESMTP id E72B26B0390 for ; Sun, 16 Apr 2017 21:48:00 -0400 (EDT) Received: by mail-pf0-f197.google.com with SMTP id o68so78976404pfj.20 for ; Sun, 16 Apr 2017 18:48:00 -0700 (PDT) Received: from mail-pg0-x242.google.com (mail-pg0-x242.google.com. [2607:f8b0:400e:c05::242]) by mx.google.com with ESMTPS id g26si9487288plj.197.2017.04.16.18.47.59 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Sun, 16 Apr 2017 18:47:59 -0700 (PDT) Received: by mail-pg0-x242.google.com with SMTP id o123so24325453pga.1 for ; Sun, 16 Apr 2017 18:47:59 -0700 (PDT) Date: Mon, 17 Apr 2017 10:48:03 +0900 From: 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 Sender: owner-linux-mm@kvack.org List-ID: 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 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 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org