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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 97E44C43334 for ; Wed, 8 Jun 2022 09:06:02 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233904AbiFHJF7 (ORCPT ); Wed, 8 Jun 2022 05:05:59 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:57658 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234238AbiFHJE2 (ORCPT ); Wed, 8 Jun 2022 05:04:28 -0400 Received: from mail-lj1-x233.google.com (mail-lj1-x233.google.com [IPv6:2a00:1450:4864:20::233]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 2B4AA222345 for ; Wed, 8 Jun 2022 01:24:21 -0700 (PDT) Received: by mail-lj1-x233.google.com with SMTP id s13so21877397ljd.4 for ; Wed, 08 Jun 2022 01:24:20 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=qn1e9UAfXz5aNABeJOAzysJEyHPbsjfCU7HdITnS84k=; b=Zf/rY8UPfUil7LCo0AmPL0ktcOejRjNbVkLs6BfbQEG0tklgICY+14UzNT7D2l+FDP kd/C58CeMvLCk8v3OokScSeoWleedGL2pCuZ4fpDA/Jq1KQDZNs4yJvNeRq2uK5ohQfv x4JYv71VyLAWcCv/E2Q2Aj30ajf43xjO6xVU0l7ZmWZuCFV8Mab02uK+G5KxWVWLxWab pz3zN5y+pykDMGv075WbOy8vrLxMM7b81TO1CCsC2Cjxlj6PBZkA0QWRSCsNtnZJpAjf OGONEqGxWA91wAD7DPtau1HbAdjZEXl/4fttRzwneXCGvy6jRrNp4vyt+nqKNTR9wue/ xJKA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=qn1e9UAfXz5aNABeJOAzysJEyHPbsjfCU7HdITnS84k=; b=aAul12IlDTKVr/LaZj+QIq2Ham7bwpEoGMs6NcHgs4Vk5H/8aPa2iei2evgSDmZObc u0Y5WenPFZ9bqn9vWCllS5XnSSN1TTxCl3IjTsAC3PEKyrx75NTTZgc+Px23EM+WukXO APdxdcu4kx8AWgLgiIcDXoXlhgBMKTPhl4Pervzo+OY2SkIePETcTCTNmQyiZCbg+TRg TDy0cGdnslCZfKJubnOwqxsA6adjwDeRuPeLw3vXbzuwdMSwfhpyqImflVfjpTN9Fd3A 49BxRYoHCf74CsXL+OKdyBmU14touLue+DDK0SboYQmUQQeBGzVoN1txLhg5PGo5glqZ Tayw== X-Gm-Message-State: AOAM531/ssu6sckTCEJP3W2Rewc0rCEfPEWPra24NNSjcuDwKZoK+amm i5JXnFdXqi+KXdI2sVSsL1IiTrJqWBmLI+2MQgFc5g== X-Google-Smtp-Source: ABdhPJwud0+3E/Q29u9oy+kzSCNdY14guBqBmA0Hqpt4c+PmhIEHReOxdmFrIBDqbHdvMdQZbHcRxllXIDLHtj3hagQ= X-Received: by 2002:a2e:bf14:0:b0:255:b789:576b with SMTP id c20-20020a2ebf14000000b00255b789576bmr3093006ljr.47.1654676659002; Wed, 08 Jun 2022 01:24:19 -0700 (PDT) MIME-Version: 1.0 References: <000000000000bb7f1c05da29b601@google.com> <00000000000010b7d305e08837c8@google.com> <20220606123839.GW2146@kadam> In-Reply-To: From: Dmitry Vyukov Date: Wed, 8 Jun 2022 10:24:07 +0200 Message-ID: Subject: Re: [syzbot] general protection fault in __device_attach To: Matthew Wilcox Cc: Dan Carpenter , Greg KH , Alan Stern , Andy Shevchenko , syzbot , hdanton@sina.com, lenb@kernel.org, linux-acpi@vger.kernel.org, linux-kernel@vger.kernel.org, rafael.j.wysocki@intel.com, rafael@kernel.org, rjw@rjwysocki.net, syzkaller-bugs@googlegroups.com, linux-usb@vger.kernel.org, Linux-MM Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-acpi@vger.kernel.org On Wed, 8 Jun 2022 at 10:20, Dmitry Vyukov wrote: > > On Tue, Jun 07, 2022 at 09:15:09AM +0200, Dmitry Vyukov wrote: > > > On Mon, 6 Jun 2022 at 14:39, Dan Carpenter wrote: > > > > > > > > On Sat, Jun 04, 2022 at 10:32:46AM +0200, 'Dmitry Vyukov' via syzkaller-bugs wrote: > > > > > On Fri, 3 Jun 2022 at 18:12, Greg KH wrote: > > > > > > > > > > > > But again, is this a "real and able to be triggered from userspace" > > > > > > problem, or just fault-injection-induced? > > > > > > > > > > Then this is something to fix in the fault injection subsystem. > > > > > Testing systems shouldn't be reporting false positives. > > > > > What allocations cannot fail in real life? Is it <=page_size? > > > > > > > > > > > > > Apparently in 2014, anything less than *EIGHT?!!* pages succeeded! > > > > > > > > https://lwn.net/Articles/627419/ > > > > > > > > I have been on the look out since that article and never seen anyone > > > > mention it changing. I think we should ignore that and say that > > > > anything over PAGE_SIZE can fail. Possibly we could go smaller than > > > > PAGE_SIZE... > > > > > > +linux-mm for GFP expertise re what allocations cannot possibly fail > > > and should be excluded from fault injection. > > > > > > Interesting, thanks for the link. > > > > > > PAGE_SIZE looks like a good start. Once we have the predicate in > > > place, we can refine it later when/if we have more inputs. > > > > > > But I wonder about GFP flags. They definitely have some impact on allocations. > > > If GFP_ACCOUNT is set, all allocations can fail, right? > > > If GFP_DMA/DMA32 is set, allocations can fail, right? What about other zones? > > > If GFP_NORETRY is set, allocations can fail? > > > What about GFP_NOMEMALLOC and GFP_ATOMIC? > > > What about GFP_IO/GFP_FS/GFP_DIRECT_RECLAIM/GFP_KSWAPD_RECLAIM? At > > > least some of these need to be set for allocations to not fail? Which > > > ones? > > > Any other flags are required to be set/unset for allocations to not fail? > > > > I'm not the expert on page allocation, but ... > > > > I don't think GFP_ACCOUNT makes allocations fail. It might make reclaim > > happen from within that cgroup, and it might cause an OOM kill for > > something in that cgroup. But I don't think it makes a (low order) > > allocation more likely to fail. > > Interesting. > I was thinking of some malicious specifically crafted configurations > with very low limit and particular pattern of allocations. Also what > if there is just 1 process (current)? Is it possible to kill and > reclaim the current process when a thread is stuck in the middle of > the kernel on a kmalloc? > Also I see e.g.: > Tasks with the OOM protection (oom_score_adj set to -1000) > are treated as an exception and are never killed. > > I am not an expert on this either, but I think it may be hard to fight > with a specifically crafted attack. > > > > There's usually less memory avilable in DMA/DMA32 zones, but we have > > so few allocations from those zones, I question the utility of focusing > > testing on those allocations. > > > > GFP_ATOMIC allows access to emergency pools, so I would say _less_ likely > > to fail. KSWAPD_RECLAIM has no effect on whether _this_ allocation > > succeeds or fails; it kicks kswapd to do reclaim, rather than doing > > reclaim directly. DIRECT_RECLAIM definitely makes allocations more likely > > to succeed. GFP_FS allows (direct) reclaim to happen from filesystems. > > GFP_IO allows IO to start (ie writeback can start) in order to clean > > dirty memory. > > > > Anyway, I hope somebody who knows the page allocator better than I do > > can say smarter things than this. Even better if they can put it into > > Documentation/ somewhere ;-) > > Even better to put this into code as a predicate function that fault > injection will use. It will also serve as precise up-to-date > documentation. Also at the end of kmalloc as: WARN_ON(!ret && !cant_fail(size, gfp)); ! > > https://www.kernel.org/doc/html/latest/core-api/memory-allocation.html > > exists but isn't quite enough to answer this question.