From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1161653AbdAEPJy (ORCPT ); Thu, 5 Jan 2017 10:09:54 -0500 Received: from mail-lf0-f51.google.com ([209.85.215.51]:34143 "EHLO mail-lf0-f51.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S938630AbdAEPJV (ORCPT ); Thu, 5 Jan 2017 10:09:21 -0500 MIME-Version: 1.0 In-Reply-To: <20170105144942.whqucdwmeqybng3s@treble> References: <20161220210144.u47znzx6qniecuvv@treble> <20161220233640.pc4goscldmpkvtqa@treble> <20161222051701.soqwh47frxwsbkni@treble> <20170105144942.whqucdwmeqybng3s@treble> From: Dmitry Vyukov Date: Thu, 5 Jan 2017 15:59:52 +0100 Message-ID: Subject: Re: x86: warning in unwind_get_return_address To: syzkaller Cc: Andrey Konovalov , Andrey Ryabinin , Alexander Potapenko , kasan-dev , "linux-mm@kvack.org" , LKML , Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , "x86@kernel.org" , Kostya Serebryany Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jan 5, 2017 at 3:49 PM, Josh Poimboeuf wrote: > On Tue, Dec 27, 2016 at 05:38:59PM +0100, Dmitry Vyukov wrote: >> On Thu, Dec 22, 2016 at 6:17 AM, Josh Poimboeuf wrote: >> > On Wed, Dec 21, 2016 at 01:46:36PM +0100, Andrey Konovalov wrote: >> >> On Wed, Dec 21, 2016 at 12:36 AM, Josh Poimboeuf wrote: >> >> > >> >> > Thanks. Looking at the stack trace, my guess is that an interrupt hit >> >> > while running in generated BPF code, and the unwinder got confused >> >> > because regs->ip points to the generated code. I may need to disable >> >> > that warning until we figure out a better solution. >> >> > >> >> > Can you share your .config file? >> >> >> >> Sure, attached. >> > >> > Ok, I was able to recreate with your config. The culprit was generated >> > code, as I suspected, though it wasn't BPF, it was a kprobe (created by >> > dccpprobe_init()). >> > >> > I'll make a patch to disable the warning. >> >> Hi, >> >> I am also seeing the following warnings: >> >> [ 281.889259] WARNING: kernel stack regs at ffff8801c29a7ea8 in >> syz-executor8:1302 has bad 'bp' value ffff8801c29a7f28 >> [ 833.994878] WARNING: kernel stack regs at ffff8801c4e77ea8 in >> syz-executor1:13094 has bad 'bp' value ffff8801c4e77f28 >> >> Can it also be caused by bpf/kprobe? > > This is a different warning. I suspect it's due to unwinding the stack > of another CPU while it's running, which is still possible in a few > places. I'm going to have to disable all these warnings for now. I also have the following diff locally. These loads trigger episodic KASAN warnings about stack-of-bounds reads on rcu stall warnings when it does backtrace of all cpus. If it looks correct to you, can you please also incorporate it into your patch? diff --git a/arch/x86/include/asm/stacktrace.h b/arch/x86/include/asm/stacktrace.h index a3269c897ec5..d8d4fc66ffec 100644 --- a/arch/x86/include/asm/stacktrace.h +++ b/arch/x86/include/asm/stacktrace.h @@ -58,7 +58,7 @@ get_frame_pointer(struct task_struct *task, struct pt_regs *regs) if (task == current) return __builtin_frame_address(0); - return (unsigned long *)((struct inactive_task_frame *)task->thread.sp)->bp; + return (unsigned long *)READ_ONCE_NOCHECK(((struct inactive_task_frame *)task->thread.sp)->bp); } #else static inline unsigned long * diff --git a/arch/x86/kernel/unwind_frame.c b/arch/x86/kernel/unwind_frame.c index 4443e499f279..f3a225ffa231 100644 --- a/arch/x86/kernel/unwind_frame.c +++ b/arch/x86/kernel/unwind_frame.c @@ -162,7 +162,7 @@ bool unwind_next_frame(struct unwind_state *state) if (state->regs) next_bp = (unsigned long *)state->regs->bp; else - next_bp = (unsigned long *)*state->bp; + next_bp = (unsigned long *)READ_ONCE_NOCHECK(*state->bp); /* is the next frame pointer an encoded pointer to pt_regs? */ regs = decode_frame_pointer(next_bp);