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=-13.4 required=3.0 tests=DKIMWL_WL_MED,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SPF_HELO_NONE,SPF_PASS,USER_IN_DEF_DKIM_WL autolearn=ham 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 763FBC433E0 for ; Sun, 14 Jun 2020 08:03:45 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 49D3B20714 for ; Sun, 14 Jun 2020 08:03:45 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="seRFgt70" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726824AbgFNIDa (ORCPT ); Sun, 14 Jun 2020 04:03:30 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40830 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725265AbgFNID3 (ORCPT ); Sun, 14 Jun 2020 04:03:29 -0400 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 2D6FDC03E969 for ; Sun, 14 Jun 2020 01:03:29 -0700 (PDT) Received: by mail-qv1-xf41.google.com with SMTP id x16so6379628qvr.3 for ; Sun, 14 Jun 2020 01:03:29 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=GiVdg0/XTq6EfadHzCxE8in79joYlrqmvBcAlMl/dg0=; b=seRFgt70D0QePUGJ8oQ/+neBFh/B0zsLl8SGjMlCXvFaOKxxsftbwQGar4WvYb7oVg gx/4n2tASXfjEPcbZkGfXR7XACVBeYUBcFjO+1Z6UXSnuWtJ5Ft+FuPQzFRSh6heVb44 nCm4I8aoJdqhb/VX6t7qoYuGfneE7W+nWkW04mvcS5gBd2cha2SFACHlnDZIby3VwZe4 e0C1PHHA4j7t3P5otMCZrsvatq/bYCVLlErvLdk5QbLzHtzySZAW6okD5pkcE3SxOmYG uqrYJCiJo5fXo/MhewL7qzl0UF3XTVKgk6RgquCVwAET8R1usRNaRqvMEA12o00E4EPR YMzA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=GiVdg0/XTq6EfadHzCxE8in79joYlrqmvBcAlMl/dg0=; b=DfOY8kF8uCHVkXOIaPlNV5D0iFKOAvZRme8+LU1LxmXiRs3JeTSfHIt7GVDXRHbTNZ 47mjdPudBXb0vK79IPojcvr9BRiK4Ckm5SoHCLP0YR0bQ9/Dmc4vTphKdLd6SoE+m+YW e0uS5w+X5mXKYbNQ+s9nbDwT9kk/F5eT83AtuHR/CrRE3w9HLA1yRKCt6VJibUJuD4yZ a/uBLAN1OtMeeA9JPC3rbX57qPJ/Bcpe5r4cus5b56CG963MA/VrzuBzFqw/Bbb3cGxR bK7ENe0ugCim4J9vnLnkD06ukysMk2hiCTxHfg/3OAvsbvOGQ+1iXeIkPGuzaLkO2vqw UBTg== X-Gm-Message-State: AOAM533YiKWalcZGY4AbxPKRBWC8uXPlzHb1Y56fZc2rvB6OF4O9dCOr nIp9iGZOospMtowbMn0Qx5/l9LylavWFvX4xtgx2sQ== X-Google-Smtp-Source: ABdhPJyfyiFN7f/pMjOwj4bUFBtAVC/GCyc2VW2CVWffBrNbuXxZMVJc2T1JMCN+KJWxiagdRDCL0E7YicHSYao7HIg= X-Received: by 2002:ad4:42b1:: with SMTP id e17mr20105422qvr.159.1592121807848; Sun, 14 Jun 2020 01:03:27 -0700 (PDT) MIME-Version: 1.0 References: <000000000000ff323f05a053100c@google.com> <20200310061525.GA30283@ubuntu-m2-xlarge-x86> In-Reply-To: From: Dmitry Vyukov Date: Sun, 14 Jun 2020 10:03:16 +0200 Message-ID: Subject: Re: general protection fault in syscall_return_slowpath To: Jann Horn Cc: syzkaller , syzbot , Borislav Petkov , "H . Peter Anvin" , kernel list , Andy Lutomirski , Ingo Molnar , syzkaller-bugs , Thomas Gleixner , "the arch/x86 maintainers" , Nathan Chancellor , Dan Carpenter Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Mar 10, 2020 at 9:10 AM Dmitry Vyukov wrote: > > On Tue, Mar 10, 2020 at 7:15 AM Nathan Chancellor > wrote: > > > > On Mon, Mar 09, 2020 at 09:20:58AM +0100, Dmitry Vyukov wrote: > > > On Sun, Mar 8, 2020 at 7:35 PM 'Jann Horn' via syzkaller-bugs > > > wrote: > > > > > > > > On Sun, Mar 8, 2020 at 5:40 PM syzbot > > > > wrote: > > > > > HEAD commit: 63623fd4 Merge tag 'for-linus' of git://git.kernel.org/pub.. > > > > > git tree: upstream > > > > > console output: https://syzkaller.appspot.com/x/log.txt?x=16cfeac3e00000 > > > > > kernel config: https://syzkaller.appspot.com/x/.config?x=5d2e033af114153f > > > > > dashboard link: https://syzkaller.appspot.com/bug?extid=cd66e43794b178bb5cd6 > > > > > compiler: clang version 10.0.0 (https://github.com/llvm/llvm-project/ c2443155a0fb245c8f17f2c1c72b6ea391e86e81) > > > > > syz repro: https://syzkaller.appspot.com/x/repro.syz?x=12a42329e00000 > > > > > > > > > > IMPORTANT: if you fix the bug, please add the following tag to the commit: > > > > > Reported-by: syzbot+cd66e43794b178bb5cd6@syzkaller.appspotmail.com > > > > > > > > > > general protection fault, probably for non-canonical address 0x1ffffffff1255a6b: 0000 [#1] PREEMPT SMP KASAN > > > > > CPU: 0 PID: 8742 Comm: syz-executor.2 Not tainted 5.6.0-rc3-syzkaller #0 > > > > > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 > > > > > RIP: 0010:arch_local_irq_disable arch/x86/include/asm/paravirt.h:757 [inline] > > > > > RIP: 0010:syscall_return_slowpath+0xeb/0x4a0 arch/x86/entry/common.c:277 > > > > > Code: 00 10 0f 85 de 00 00 00 e8 b2 a3 76 00 48 c7 c0 58 d3 2a 89 48 c1 e8 03 80 3c 18 00 74 0c 48 c7 c7 58 d3 2a 89 e8 05 00 00 00 <00> 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 > > > > > RSP: 0018:ffffc900020a7ed0 EFLAGS: 00010246 > > > > > RAX: 1ffffffff1255a6b RBX: dffffc0000000000 RCX: ffff88808c512380 > > > > > RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000 > > > > > RBP: ffffc900020a7f10 R08: ffffffff810075bb R09: fffffbfff14d9182 > > > > > R10: fffffbfff14d9182 R11: 0000000000000000 R12: 1ffff110118a2470 > > > > > R13: 0000000000004000 R14: ffff88808c512380 R15: ffff88808c512380 > > > > > FS: 000000000154f940(0000) GS:ffff8880aea00000(0000) knlGS:0000000000000000 > > > > > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > > > > > CR2: 000000000076c000 CR3: 00000000a6b05000 CR4: 00000000001406f0 > > > > > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 > > > > > DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 > > > > > Call Trace: > > > > > do_syscall_64+0x11f/0x1c0 arch/x86/entry/common.c:304 > > > > > entry_SYSCALL_64_after_hwframe+0x49/0xbe > > > > > BUG: kernel NULL pointer dereference, address: 0000000000000000 > > > > > #PF: supervisor write access in kernel mode > > > > > #PF: error_code(0x0002) - not-present page > > > > > PGD 8fecc067 P4D 8fecc067 PUD 97953067 PMD 0 > > > > > Oops: 0002 [#2] PREEMPT SMP KASAN > > > > > CPU: 0 PID: 8742 Comm: syz-executor.2 Not tainted 5.6.0-rc3-syzkaller #0 > > > > > > > > Ugh, why does it build with -Werror... > > > > There are certain warnings that are specifically treated like errors: > > > > In the main Makefile: > > > > KBUILD_CFLAGS += $(call cc-option,-Werror=incompatible-pointer-types) > > > > > Now I am realizing I don't know what's the proper way to turn off > > > warnings entirely... > > > > > > We turn off this CONFIG_ERROR_ON_WARNING historically: > > > https://github.com/google/syzkaller/blob/2e9971bbbfb4df6ba0118353163a7703f3dbd6ec/dashboard/config/bits-syzbot.config#L17 > > > and I thought that's enough. But now I realize it's not even a thing. > > > I see it referenced in some ChromeOS threads and there are some > > > discussions re upstreaming, but apparently it never existed upstream. > > > > > > make has W=n, but it seems that it can only be used to produce more > > > warnings. We don't pass W=3 specifically and there is no W=0. > > > > > > Should we always build with CFLAGS=-w? Is it guaranteed to work? Or is > > > there a better way? > > > > Would passing -Wno-werror via KCFLAGS work? Otherwise, passing > > -Wno-error= should work. > > > > Cheers, > > Nathan > > Filed https://github.com/google/syzkaller/issues/1635 so that this is not lost. Jann, Getting back to this. Are you sure building without warning will be better? Currently make enables these warnings as errors only: -Werror=strict-prototypes -Werror=implicit-function-declaration -Werror=implicit-int -Werror=date-time -Werror=incompatible-pointer-types -Werror=designated-init So most warnings won't cause build failure. And, say, converting T* to Y* implicitly may be an actual bug in the patch. The other concern is that some people may use syzbot testing as the only patch testing and then submit a patch that breaks build...