From: Peter Zijlstra <peterz@infradead.org>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: syzbot
<bot+72c44cd8b0e8a1a64b9c03c4396aea93a16465ef@syzkaller.appspotmail.com>,
Ingo Molnar <mingo@redhat.com>,
Andrew Morton <akpm@linux-foundation.org>,
Dave Jiang <dave.jiang@intel.com>,
Hugh Dickins <hughd@google.com>, Jan Kara <jack@suse.cz>,
Jerome Glisse <jglisse@redhat.com>,
"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
linux-mm <linux-mm@kvack.org>, tcharding <me@tobin.cc>,
Michal Hocko <mhocko@suse.com>, Minchan Kim <minchan@kernel.org>,
Ross Zwisler <ross.zwisler@linux.intel.com>,
syzkaller-bugs@googlegroups.com,
Matthew Wilcox <willy@infradead.org>
Subject: Re: general protection fault in finish_task_switch
Date: Fri, 22 Dec 2017 09:17:56 +0100 [thread overview]
Message-ID: <20171222081756.ur5uuh5wjri2ymyk@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <CA+55aFyco00CBed1ADAz+EGtoP6w+nvuR2Y+YWH13cvkatOg4w@mail.gmail.com>
On Thu, Dec 21, 2017 at 10:42:04AM -0800, Linus Torvalds wrote:
> On Wed, Dec 20, 2017 at 8:03 AM, syzbot
> <bot+72c44cd8b0e8a1a64b9c03c4396aea93a16465ef@syzkaller.appspotmail.com>
> wrote:
> > Hello,
> >
> > syzkaller hit the following crash on
> > 7dc9f647127d6955ffacaf51cb6a627b31dceec2
> > git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/master
> >
> > kasan: CONFIG_KASAN_INLINE enabled
> > kasan: GPF could be caused by NULL-ptr deref or user memory access
> > general protection fault: 0000 [#1] SMP KASAN
> > Dumping ftrace buffer:
> > (ftrace buffer empty)
> > Modules linked in:
> > CPU: 0 PID: 4227 Comm: syzkaller244813 Not tainted 4.15.0-rc4-next-20171220+
> > #77
> > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
> > Google 01/01/2011
> > RIP: __fire_sched_in_preempt_notifiers kernel/sched/core.c:2534 [inline]
>
> That line 2534 is the call inside the hlist_for_each_entry() loop:
>
> hlist_for_each_entry(notifier, &curr->preempt_notifiers, link)
> notifier->ops->sched_in(notifier, raw_smp_processor_id());
>
> and the Code: line disassembly is
>
> 0: ff 11 callq *(%rcx)
> 2: 4c 89 f9 mov %r15,%rcx
> 5: 48 c1 e9 03 shr $0x3,%rcx
> 9: 42 80 3c 31 00 cmpb $0x0,(%rcx,%r14,1)
> e: 0f 85 1b 02 00 00 jne 0x22f
> 14: 4d 8b 3f mov (%r15),%r15
> 17: 4d 85 ff test %r15,%r15
> 1a: 0f 84 c0 fd ff ff je 0xfffffffffffffde0
> 20: 49 8d 7f 10 lea 0x10(%r15),%rdi
> 24: 48 89 f9 mov %rdi,%rcx
> 27: 48 c1 e9 03 shr $0x3,%rcx
> 2b:* 42 80 3c 31 00 cmpb $0x0,(%rcx,%r14,1) <-- trapping instruction
> 30: 74 ae je 0xffffffffffffffe0
> 32: e8 a7 cc 5b 00 callq 0x5bccde
> 37: eb a7 jmp 0xffffffffffffffe0
> 39: 4c 89 fe mov %r15,%rsi
> 3c: 4c 89 e7 mov %r12,%rdi
>
> and while the "callq *(%rcx)" might be just the end part of some
> previous instruction, I think it may be right (there is indeed an
> indirect call in that function - that very "->sched_in()" call).
>
> So I think the oops happens after the indirect call returns.
>
> I think the second "callq" is
>
> call __asan_report_load8_noabort
>
> and the actual trapping instruction is loading the KASAN byte state.
>
> As far as I can tell, the kasan check is trying to check this part of
> hlist_for_each_entry():
>
> movq (%r15), %r15 # notifier_110->link.next,
>
> and %r15 is dead000000000100, which is LIST_POISON1.
>
> End result: KASAN actually makes these things harder to debug, because
> it's trying to "validate" the list poison values before they are used,
> and takes a much more complex and indirect fault in the process,
> instead of just getting a page-fault on the LIST_POISON1 that would
> have made it more obvious.
>
> Oh well.
>
> There is nothing in this that indicates that it's actually related to
> KASAN, and it _should_ oops even without KASAN enabled.
>
> But the reproducer does nothing for me. Of course, I didn't actually
> run it on linux-next at all, so it is quite possibly related to
> scheduler work (or the TLB/pagetable work) that just hasn't hit
> mainstream yet.
>
> None of the scheduler people seem to have been on the report, though.
> Adding some in.
So the only user of that preempt_notifier stuff is KVM, if you don't run
a guest the notifiers are empty and are in fact disabled with a
static_key.
We've not touched this part of the scheduler in a fair while. I'll go
dig out the original report and see if that reproducer does anything for
me.
next prev parent reply other threads:[~2017-12-22 8:18 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-12-20 16:03 general protection fault in finish_task_switch syzbot
2017-12-21 18:42 ` Linus Torvalds
2017-12-22 8:17 ` Peter Zijlstra [this message]
2017-12-22 8:26 ` Dmitry Vyukov
2017-12-22 8:36 ` Peter Zijlstra
2017-12-22 8:44 ` Dmitry Vyukov
2017-12-22 8:57 ` Peter Zijlstra
2017-12-22 9:08 ` Dmitry Vyukov
2017-12-22 9:30 ` Peter Zijlstra
2017-12-22 9:48 ` Dmitry Vyukov
2017-12-22 10:03 ` Peter Zijlstra
2017-12-22 10:24 ` Dmitry Vyukov
2017-12-22 10:37 ` Peter Zijlstra
2017-12-22 8:37 ` Dmitry Vyukov
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