From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-15.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 85E87C433FE for ; Fri, 4 Dec 2020 15:11:17 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4EA7322B3B for ; Fri, 4 Dec 2020 15:11:17 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726412AbgLDPLQ (ORCPT ); Fri, 4 Dec 2020 10:11:16 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43846 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725923AbgLDPLQ (ORCPT ); Fri, 4 Dec 2020 10:11:16 -0500 Received: from mail-qv1-xf41.google.com (mail-qv1-xf41.google.com [IPv6:2607:f8b0:4864:20::f41]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B35FBC061A4F for ; Fri, 4 Dec 2020 07:10:30 -0800 (PST) Received: by mail-qv1-xf41.google.com with SMTP id es6so2875037qvb.7 for ; Fri, 04 Dec 2020 07:10:30 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=ziepe.ca; s=google; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=kBeUn5P5wE5MCbsqxhOqI6oHNmGrXnrLIbqNK49mm0I=; b=FMZKxOrWV/Gw3vq3n73axTVe6lyEaokINiMM9qlxoM9F38QY6zzkdEhvyprzTWWyBi Meno/+YIx7OOOuYAgj6kt7vNHYaUDObhdq/nEKTSerjT/g4OMEjEQoKsrTyL1dnkomXN fE6Rz8mwWmYMzGXzFtHVZLrxa4n0/rni0C+aSsEG6sBvT38CoeBIX05SOV6JUEqLB6/9 hHPEesYfv6QaxmBtUJY0c4LU28NqcmdzS+HemA9AIsxoUjgoa7pqcTrp40uHszaH1xga Eprc+Vy59MW0OaP5kAQdvWpkKF06KKbSLrwcMrwH82Ypht0vovxncPOhHfjMlpKUmSxE VbBw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=kBeUn5P5wE5MCbsqxhOqI6oHNmGrXnrLIbqNK49mm0I=; b=d/1rhfXHTPCqNNjHAXl+34sv02rRaD2VftsZV7GgfoOEVd35X7fXI6aLwlylOFfQRt U4QEgbZwVuVh3TDkW4UJXEz9nr5AsV9rvIxqTz24Twp21nuZ6HkoILUwemIhe9INyeBy kMi/sYQ3J66PRqhSJ7DI7pmRH6bvN80BS7sCmDIhTLQa6VWkpW83dFn+ywXiBEtvb3Kz UhW3gqJNPRUmO0BImx8Ts0xnFX4pughFeGnpI8SeNTJ4hDqK0/mx7h1hLxHLvrmNi3Hs 5h52GWu7sMDk6eIR3Rw+70r4e62bO+LVDNGW28r4DGAk5gkkmopi/ZYwaXn5DopR2egq ZUcw== X-Gm-Message-State: AOAM531Xx3tjGA77qLmfpsB54ZH3sERzuk/oHB1QPrq0uymEN2aKFo+z yBdFC8Qh8hE6NQyhFI8TCgnB/Q8XmOqWBQ== X-Google-Smtp-Source: ABdhPJxufNqV7sKpWrPaM1CPV1hhTtTtEsP4V5Ga0AZ4MKMdNca+YZDsulis5sl7uI/XxhICi8LS6Q== X-Received: by 2002:a0c:bf0f:: with SMTP id m15mr5766682qvi.23.1607094629954; Fri, 04 Dec 2020 07:10:29 -0800 (PST) Received: from ziepe.ca ([206.223.160.26]) by smtp.gmail.com with ESMTPSA id o9sm5206035qte.35.2020.12.04.07.10.29 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 04 Dec 2020 07:10:29 -0800 (PST) Received: from jgg by mlx with local (Exim 4.94) (envelope-from ) id 1klCj6-005uXv-6R; Fri, 04 Dec 2020 11:10:28 -0400 Date: Fri, 4 Dec 2020 11:10:28 -0400 From: Jason Gunthorpe To: David Hildenbrand Cc: Liu Zixian , akpm@linux-foundation.org, linmiaohe@huawei.com, louhongxiang@huawei.com, linux-mm@kvack.org, hushiyuan@huawei.com, stable@vger.kernel.org Subject: Re: [PATCH v2] fix mmap return value when vma is merged after call_mmap() Message-ID: <20201204151028.GZ5487@ziepe.ca> References: <20201203085350.22624-1-liuzixian4@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org On Fri, Dec 04, 2020 at 03:11:54PM +0100, David Hildenbrand wrote: > On 03.12.20 09:53, Liu Zixian wrote: > > On success, mmap should return the begin address of newly mapped area, > > but patch "mm: mmap: merge vma after call_mmap() if possible" > > set vm_start of newly merged vma to return value addr. > > Users of mmap will get wrong address if vma is merged after call_mmap(). > > We fix this by moving the assignment to addr before merging vma. > > > > Fixes: d70cec898324 ("mm: mmap: merge vma after call_mmap() if possible") > > Signed-off-by: Liu Zixian > > v2: > > We want to do "addr = vma->vm_start;" unconditionally, > > so move assignment to addr before if(unlikely) block. > > mm/mmap.c | 26 ++++++++++++-------------- > > 1 file changed, 12 insertions(+), 14 deletions(-) > > > > diff --git a/mm/mmap.c b/mm/mmap.c > > index d91ecb00d38c..5c8b4485860d 100644 > > +++ b/mm/mmap.c > > @@ -1808,6 +1808,17 @@ unsigned long mmap_region(struct file *file, unsigned long addr, > > if (error) > > goto unmap_and_free_vma; > > > > + /* Can addr have changed?? > > + * > > + * Answer: Yes, several device drivers can do it in their > > + * f_op->mmap method. -DaveM > > + * Bug: If addr is changed, prev, rb_link, rb_parent should > > + * be updated for vma_link() > > + */ > > > Why do we tolerate device drivers doing such stuff at all? > WARN_ON_ONCE() is just as good as BUG_ON() in many environments. If we > support it, then no warning. If we don't support it, then why tolerate it? The commit that introduced this seemed pretty clear it is to catch possibly wrong drivers. I suppose the idea was to give a migration time where things would "work" and drivers could be fixed. Since it has now been 8 years it should be either dropped or turned into: /* Drivers are not permitted to change vm_start */ if (WARN_ON(addr != vma->vm_start)) { err = EINVAL goto unmap_and_free_vma } commit 2897b4d29d9fca82a57b09b8a216a5d604966e4b Author: Joonsoo Kim Date: Wed Dec 12 13:51:53 2012 -0800 mm: WARN_ON_ONCE if f_op->mmap() change vma's start address During reviewing the source code, I found a comment which mention that after f_op->mmap(), vma's start address can be changed. I didn't verify that it is really possible, because there are so many f_op->mmap() implementation. But if there are some mmap() which change vma's start address, it is possible error situation, because we already prepare prev vma, rb_link and rb_parent and these are related to original address. So add WARN_ON_ONCE for finding that this situtation really happens. Jason