From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753311AbdLNPbb (ORCPT ); Thu, 14 Dec 2017 10:31:31 -0500 Received: from Galois.linutronix.de ([146.0.238.70]:37734 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753280AbdLNPb3 (ORCPT ); Thu, 14 Dec 2017 10:31:29 -0500 Date: Thu, 14 Dec 2017 16:31:27 +0100 (CET) From: Thomas Gleixner To: syzbot cc: Darren Hart , LKML , Ingo Molnar , Peter Zijlstra , syzkaller-bugs@googlegroups.com, Andrey Ryabinin , Alexander Potapenko , Dmitry Vyukov Subject: Re: BUG: unable to handle kernel paging request in do_futex In-Reply-To: <001a113ed15ed79d14055f379011@google.com> Message-ID: References: <001a113ed15ed79d14055f379011@google.com> User-Agent: Alpine 2.20 (DEB 67 2015-01-07) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 30 Nov 2017, syzbot wrote: > Hello, > > syzkaller hit the following crash on 11fed7829beff10184503fd65e5919926464601a > git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/master > compiler: gcc (GCC) 7.1.1 20170620 > .config is attached > Raw console output is attached. > > Unfortunately, I don't have any reproducer for this bug yet. > > > BUG: unable to handle kernel paging request at 00000000c314149f That's a user space address which is nowhere in the registers. Is that perhaps pre commit: 328b4ed93b69a ? > IP: arch_futex_atomic_op_inuser arch/x86/include/asm/futex.h:67 [inline] > IP: futex_atomic_op_inuser kernel/futex.c:1588 [inline] > IP: futex_wake_op kernel/futex.c:1637 [inline] > IP: do_futex+0x14c8/0x2280 kernel/futex.c:3483 > PGD 5e28067 P4D 5e28067 PUD 5e2a067 PMD 0 > Oops: 0002 [#1] SMP KASAN ^^^^ X86_PF_WRITE > Dumping ftrace buffer: > (ftrace buffer empty) > Modules linked in: > CPU: 0 PID: 14626 Comm: syz-executor6 Not tainted 4.15.0-rc1-next-20171130+ > #56 > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google > 01/01/2011 > task: 000000005f17dad6 task.stack: 000000005af7607c > RIP: 0010:arch_futex_atomic_op_inuser arch/x86/include/asm/futex.h:67 [inline] > RIP: 0010:futex_atomic_op_inuser kernel/futex.c:1588 [inline] > RIP: 0010:futex_wake_op kernel/futex.c:1637 [inline] > RIP: 0010:do_futex+0x14c8/0x2280 kernel/futex.c:3483 > RSP: 0018:ffff8801cffafa18 EFLAGS: 00010246 > RAX: 000000007fffffff RBX: 0000000040000002 RCX: ffffffff8164e3d9 > RDX: 0000000000000000 RSI: ffffc900034e8000 RDI: 0000000000000000 > RBP: ffff8801cffafe38 R08: 1ffffffff0d31367 R09: 0000000000000004 > R10: 0000000000000000 R11: ffffffff8748cd60 R12: ffff8801d0f30180 > R13: 0000000020000000 R14: dffffc0000000000 R15: ffff8801cffafe10 > FS: 00007f66305e0700(0000) GS:ffff8801db400000(0000) knlGS:0000000000000000 > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > CR2: fffffffffffffff8 CR3: 00000001ccc2e000 CR4: 00000000001426f0 ^^^^^^^^^^^^^^^^ is a totally different address so its either completely bogus or the above address is a hashed pointer because that printk used to be %p and was changed to %px in 328b4ed93b69a > DR0: 0000000020000000 DR1: 0000000020000000 DR2: 0000000000000000 > DR3: 0000000000000000 DR6: 00000000ffff0ff3 DR7: 0000000000bb060a > Call Trace: > SYSC_futex kernel/futex.c:3533 [inline] > SyS_futex+0x260/0x390 kernel/futex.c:3501 > entry_SYSCALL_64_fastpath+0x1f/0x96 > RIP: 0033:0x4529d9 > RSP: 002b:00007f66305dfc58 EFLAGS: 00000212 ORIG_RAX: 00000000000000ca > RAX: ffffffffffffffda RBX: 00007f66305e0700 RCX: 00000000004529d9 > RDX: 0000000000000007 RSI: 0000000000000085 RDI: 0000000020062000 > RBP: 0000000000000000 R08: 0000000020000000 R09: 0000000040000002 > R10: 000000002085fff0 R11: 0000000000000212 R12: 0000000000000000 > R13: 0000000000a6f7ff R14: 00007f66305e09c0 R15: 0000000000000000 The arguments are: RDI uaddr 0000000020062000 RSI op 0000000000000085 RDX val 0000000000000007 RCX utime 00000000004529d9 R8 uaddr2 0000000020000000 R9 val2 0000000040000002 > Code: 31 d2 0f 1f 00 45 87 65 00 0f 1f 00 89 95 30 fc ff ff e9 1d ff ff ff e8 > 67 56 0b 00 31 d2 8b bd 00 fc ff ff 0f 1f 00 41 8b 45 00 <89> c1 31 f9 f0 41 > 0f b1 4d 00 75 f0 0f 1f 00 41 89 c4 89 95 30 and the code is: 27: 41 8b 45 00 mov 0x0(%r13),%eax 2b:* 89 c1 mov %eax,%ecx <-- trapping instruction 2d: 31 f9 xor %edi,%ecx 2f: f0 41 0f b1 4d 00 lock cmpxchg %ecx,0x0(%r13) 35: 75 f0 jne 0x27 The trapping instruction cannot trap :). Assumed it's the move before that, then the accessed location is R13 + 0 = 0000000020000000, which is uaddr2 and entirely correct. And what I completely fail to understand why this triggers at all. That code section is guarded by an extable fixup so this should never come in. Is this a KASAN artifact? Thanks, tglx