linux-kernel - Re: WARNING: can't access registers at asm_sysvec_call_function

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Date:   Tue, 15 Sep 2020 09:19:13 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Dmitry Vyukov <dvyukov@...gle.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        syzbot <syzbot+bc9dbf05dcc151e9b972@...kaller.appspotmail.com>,
        alexandre.chartre@...cle.com, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Andy Lutomirski <luto@...nel.org>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        the arch/x86 maintainers <x86@...nel.org>
Subject: Re: WARNING: can't access registers at
 asm_sysvec_call_function_single

On Tue, Sep 15, 2020 at 06:27:25AM +0200, Dmitry Vyukov wrote:
> On Mon, Sep 14, 2020 at 6:51 PM Josh Poimboeuf <jpoimboe@...hat.com> wrote:
> > > > On Tue, Sep 08 2020 at 13:16, syzbot wrote:
> > > >
> > > > > Hello,
> > > > >
> > > > > syzbot found the following issue on:
> > > > >
> > > > > HEAD commit:    f4d51dff Linux 5.9-rc4
> > > > > git tree:       upstream
> > > > > console output: https://syzkaller.appspot.com/x/log.txt?x=1455d4f9900000
> > > > > kernel config:  https://syzkaller.appspot.com/x/.config?x=a9075b36a6ae26c9
> > > > > dashboard link: https://syzkaller.appspot.com/bug?extid=bc9dbf05dcc151e9b972
> > > > > compiler:       gcc (GCC) 10.1.0-syz 20200507
> > > > >
> > > > > Unfortunately, I don't have any reproducer for this issue yet.
> > > > >
> > > > > IMPORTANT: if you fix the issue, please add the following tag to the commit:
> > > > > Reported-by: syzbot+bc9dbf05dcc151e9b972@...kaller.appspotmail.com
> > > > >
> > > > > WARNING: can't access registers at asm_sysvec_call_function_single+0x12/0x20 arch/x86/include/asm/idtentry.h:589
> > > >
> > > > That's the ORC unwinder complaining, but I have no idea why...
> > >
> > > 0000000000000cd0 <asm_sysvec_call_function_single>:
> > >      cd0:     90                      nop
> > >      cd1:     90                      nop
> > >      cd2:     90                      nop
> > >      cd3:     6a ff                   pushq  $0xffffffffffffffff
> > >      cd5:     e8 b6 03 00 00          callq  1090 <error_entry>
> > >      cda:     48 89 e7                mov    %rsp,%rdi
> > >      cdd:     e8 00 00 00 00          callq  ce2 <asm_sysvec_call_function_single+0x12>
> > >                       cde: R_X86_64_PLT32     sysvec_call_function_single-0x4
> > >      ce2:     e9 69 04 00 00          jmpq   1150 <error_return>
> > >      ce7:     66 0f 1f 84 00 00 00    nopw   0x0(%rax,%rax,1)
> > >      cee:     00 00
> > >
> > > This is a head scratcher.  The ORC data looks ok, at least when I build
> > > it on my system.  It's expecting to find pt_regs at the top of the stack
> > > after returning from sysvec_call_function_single().  But it can't
> > > dereference the regs for some reason.
> > >
> > > So either it's a bug in ORC data or unwinder (not likely) or the stack
> > > pointer got corrupted somehow (also seems unlikely)...
> >
> > The true bug may be revealed elsewhere on the stack... I probably need
> > to start enabling ORC stack dumps like I did for FP.
> 
> Hi Josh,
> 
> Is there a config for this? We could enable it on syzbot. More
> informative kernel diagnostics are always better.

Unfortunately the ORC dump code doesn't exist upstream yet.  I need to
dust the patches off and post.

-- 
Josh