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From:   Dmitry Vyukov <dvyukov@google.com>
Date:   Fri, 29 May 2020 15:20:21 +0200
Message-ID: <CACT4Y+ajjB8RmG3_H_9r-kaRAZ05ejW02-Py47o7wkkBjwup3Q@mail.gmail.com>
Subject: Re: PANIC: double fault in fixup_bad_iret
To:     syzbot <syzbot+dc1fa714cb070b184db5@syzkaller.appspotmail.com>
Cc:     LKML <linux-kernel@vger.kernel.org>,
        syzkaller-bugs <syzkaller-bugs@googlegroups.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        "the arch/x86 maintainers" <x86@kernel.org>,
        Oleg Nesterov <oleg@redhat.com>
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Sender: linux-kernel-owner@vger.kernel.org
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On Fri, May 29, 2020 at 3:14 PM syzbot
<syzbot+dc1fa714cb070b184db5@syzkaller.appspotmail.com> wrote:
>
> Hello,
>
> syzbot found the following crash on:
>
> HEAD commit:    7b4cb0a4 Add linux-next specific files for 20200525
> git tree:       linux-next
> console output: https://syzkaller.appspot.com/x/log.txt?x=15dc34ba100000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=47b0740d89299c10
> dashboard link: https://syzkaller.appspot.com/bug?extid=dc1fa714cb070b184db5
> compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=14678626100000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1017ef06100000
>
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+dc1fa714cb070b184db5@syzkaller.appspotmail.com

From the reproducer it seems to be either x86 related or ptrace related.

> traps: PANIC: double fault, error_code: 0x0
> double fault: 0000 [#1] PREEMPT SMP KASAN
> CPU: 0 PID: 7280 Comm: syz-executor776 Not tainted 5.7.0-rc7-next-20200525-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> RIP: 0010:fixup_bad_iret+0x24/0x170 arch/x86/kernel/traps.c:665
> Code: eb cb 0f 1f 40 00 41 55 49 bd 00 00 00 00 00 fc ff df 41 54 55 48 89 fd 48 c7 c7 80 8a 25 88 53 48 81 ec 40 01 00 00 48 89 e3 <48> c7 04 24 b3 8a b5 41 48 c7 44 24 08 bf d3 49 89 48 c1 eb 03 48
> RSP: 0018:fffffe0000001fb8 EFLAGS: 00010086
> RAX: fffffffffffffff7 RBX: fffffe0000001fb8 RCX: ffffffff87e00d57
> RDX: 0000000000000000 RSI: ffffffff87e009c8 RDI: ffffffff88258a80
> RBP: fffffe0000002120 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
> R13: dffffc0000000000 R14: 0000000000000000 R15: 0000000000000000
> FS:  0000000001f65880(0000) GS:ffff8880ae600000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: fffffe0000001fa8 CR3: 00000000a02aa000 CR4: 00000000001406f0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
>  <ENTRY_TRAMPOLINE>
>  error_entry+0xb8/0xc0 arch/x86/entry/entry_64.S:1375
> RIP: 0010:native_irq_return_iret+0x0/0x2
> Code: 5a 41 59 41 58 58 59 5a 5e 5f 48 83 c4 08 e9 10 00 00 00 90 0f 1f 44 00 00 66 2e 0f 1f 84 00 00 00 00 00 f6 44 24 20 04 75 02 <48> cf 57 0f 01 f8 0f 1f 00 65 48 8b 3c 25 00 b0 01 00 48 89 07 48
> RSP: 0018:fffffe00000021d8 EFLAGS: 00010046 ORIG_RAX: 0000000000000000
> RAX: fffffffffffffff7 RBX: 0000000000000000 RCX: 0000000000000000
> RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000020000100
> RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
> R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
> RIP: 0033:0x3bfd19e0df38d197
> Code: Bad RIP value.
> RSP: 002b:00007fffaaa547c8 EFLAGS: 00000346 </ENTRY_TRAMPOLINE>
> Modules linked in:
> ---[ end trace d6561a908e3835a1 ]---
> RIP: 0010:fixup_bad_iret+0x24/0x170 arch/x86/kernel/traps.c:665
> Code: eb cb 0f 1f 40 00 41 55 49 bd 00 00 00 00 00 fc ff df 41 54 55 48 89 fd 48 c7 c7 80 8a 25 88 53 48 81 ec 40 01 00 00 48 89 e3 <48> c7 04 24 b3 8a b5 41 48 c7 44 24 08 bf d3 49 89 48 c1 eb 03 48
> RSP: 0018:fffffe0000001fb8 EFLAGS: 00010086
> RAX: fffffffffffffff7 RBX: fffffe0000001fb8 RCX: ffffffff87e00d57
> RDX: 0000000000000000 RSI: ffffffff87e009c8 RDI: ffffffff88258a80
> RBP: fffffe0000002120 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
> R13: dffffc0000000000 R14: 0000000000000000 R15: 0000000000000000
> FS:  0000000001f65880(0000) GS:ffff8880ae600000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: fffffe0000001fa8 CR3: 00000000a02aa000 CR4: 00000000001406f0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
>
>
> ---
> This bug is generated by a bot. It may contain errors.
> See https://goo.gl/tpsmEJ for more information about syzbot.
> syzbot engineers can be reached at syzkaller@googlegroups.com.
>
> syzbot will keep track of this bug report. See:
> https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
> syzbot can test patches for this bug, for details see:
> https://goo.gl/tpsmEJ#testing-patches
>
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