From: Sean Christopherson <sean.j.christopherson@intel.com>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: "Daniel Díaz" <daniel.diaz@linaro.org>,
"Naresh Kamboju" <naresh.kamboju@linaro.org>,
"Stephen Rothwell" <sfr@canb.auug.org.au>,
"Matthew Wilcox (Oracle)" <willy@infradead.org>,
zenglg.jy@cn.fujitsu.com,
"Peter Zijlstra (Intel)" <peterz@infradead.org>,
"Viresh Kumar" <viresh.kumar@linaro.org>,
"X86 ML" <x86@kernel.org>,
"open list" <linux-kernel@vger.kernel.org>,
lkft-triage@lists.linaro.org,
"Eric W. Biederman" <ebiederm@xmission.com>,
linux-mm <linux-mm@kvack.org>,
linux-m68k <linux-m68k@lists.linux-m68k.org>,
"Linux-Next Mailing List" <linux-next@vger.kernel.org>,
"Thomas Gleixner" <tglx@linutronix.de>,
kasan-dev <kasan-dev@googlegroups.com>,
"Dmitry Vyukov" <dvyukov@google.com>,
"Geert Uytterhoeven" <geert@linux-m68k.org>,
"Christian Brauner" <christian.brauner@ubuntu.com>,
"Ingo Molnar" <mingo@redhat.com>, "LTP List" <ltp@lists.linux.it>,
"Al Viro" <viro@zeniv.linux.org.uk>
Subject: Re: [LTP] mmstress[1309]: segfault at 7f3d71a36ee8 ip 00007f3d77132bdf sp 00007f3d71a36ee8 error 4 in libc-2.27.so[7f3d77058000+1aa000]
Date: Thu, 22 Oct 2020 22:02:14 -0700 [thread overview]
Message-ID: <20201023050214.GG23681@linux.intel.com> (raw)
In-Reply-To: <CAHk-=wgqAp5B46SWzgBt6UkheVGFPs2rrE6H4aqLExXE1TXRfQ@mail.gmail.com>
On Thu, Oct 22, 2020 at 08:05:05PM -0700, Linus Torvalds wrote:
> On Thu, Oct 22, 2020 at 6:36 PM Daniel Díaz <daniel.diaz@linaro.org> wrote:
> >
> > The kernel Naresh originally referred to is here:
> > https://builds.tuxbuild.com/SCI7Xyjb7V2NbfQ2lbKBZw/
>
> Thanks.
>
> And when I started looking at it, I realized that my original idea
> ("just look for __put_user_nocheck_X calls, there aren't so many of
> those") was garbage, and that I was just being stupid.
>
> Yes, the commit that broke was about __put_user(), but in order to not
> duplicate all the code, it re-used the regular put_user()
> infrastructure, and so all the normal put_user() calls are potential
> problem spots too if this is about the compiler interaction with KASAN
> and the asm changes.
>
> So it's not just a couple of special cases to look at, it's all the
> normal cases too.
>
> Ok, back to the drawing board, but I think reverting it is probably
> the right thing to do if I can't think of something smart.
>
> That said, since you see this on x86-64, where the whole ugly trick with that
>
> register asm("%"_ASM_AX)
>
> is unnecessary (because the 8-byte case is still just a single
> register, no %eax:%edx games needed), it would be interesting to hear
> if the attached patch fixes it. That would confirm that the problem
> really is due to some register allocation issue interaction (or,
> alternatively, it would tell me that there's something else going on).
I haven't reproduced the crash, but I did find a smoking gun that confirms the
"register shenanigans are evil shenanigans" theory. I ran into a similar thing
recently where a seemingly innocuous line of code after loading a value into a
register variable wreaked havoc because it clobbered the input register.
This put_user() in schedule_tail():
if (current->set_child_tid)
put_user(task_pid_vnr(current), current->set_child_tid);
generates the following assembly with KASAN out-of-line:
0xffffffff810dccc9 <+73>: xor %edx,%edx
0xffffffff810dcccb <+75>: xor %esi,%esi
0xffffffff810dcccd <+77>: mov %rbp,%rdi
0xffffffff810dccd0 <+80>: callq 0xffffffff810bf5e0 <__task_pid_nr_ns>
0xffffffff810dccd5 <+85>: mov %r12,%rdi
0xffffffff810dccd8 <+88>: callq 0xffffffff81388c60 <__asan_load8>
0xffffffff810dccdd <+93>: mov 0x590(%rbp),%rcx
0xffffffff810dcce4 <+100>: callq 0xffffffff817708a0 <__put_user_4>
0xffffffff810dcce9 <+105>: pop %rbx
0xffffffff810dccea <+106>: pop %rbp
0xffffffff810dcceb <+107>: pop %r12
__task_pid_nr_ns() returns the pid in %rax, which gets clobbered by
__asan_load8()'s check on current for the current->set_child_tid dereference.
next prev parent reply other threads:[~2020-10-23 5:02 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-21 16:58 mmstress[1309]: segfault at 7f3d71a36ee8 ip 00007f3d77132bdf sp 00007f3d71a36ee8 error 4 in libc-2.27.so[7f3d77058000+1aa000] Naresh Kamboju
2020-10-21 17:05 ` Linus Torvalds
2020-10-21 17:22 ` Naresh Kamboju
2020-10-22 20:55 ` Naresh Kamboju
2020-10-22 23:43 ` Linus Torvalds
2020-10-23 0:11 ` Linus Torvalds
2020-10-23 0:22 ` Linus Torvalds
2020-10-23 1:36 ` [LTP] " Daniel Díaz
2020-10-23 3:05 ` Linus Torvalds
2020-10-23 5:02 ` Sean Christopherson [this message]
2020-10-23 7:14 ` Rasmus Villemoes
2020-10-23 15:54 ` Linus Torvalds
2020-10-23 16:32 ` Linus Torvalds
2020-10-23 17:50 ` Naresh Kamboju
2020-10-23 15:52 ` Linus Torvalds
2020-10-23 17:00 ` Naresh Kamboju
2020-10-23 17:50 ` Linus Torvalds
2020-10-23 21:15 ` Song Liu
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20201023050214.GG23681@linux.intel.com \
--to=sean.j.christopherson@intel.com \
--cc=christian.brauner@ubuntu.com \
--cc=daniel.diaz@linaro.org \
--cc=dvyukov@google.com \
--cc=ebiederm@xmission.com \
--cc=geert@linux-m68k.org \
--cc=kasan-dev@googlegroups.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-m68k@lists.linux-m68k.org \
--cc=linux-mm@kvack.org \
--cc=linux-next@vger.kernel.org \
--cc=lkft-triage@lists.linaro.org \
--cc=ltp@lists.linux.it \
--cc=mingo@redhat.com \
--cc=naresh.kamboju@linaro.org \
--cc=peterz@infradead.org \
--cc=sfr@canb.auug.org.au \
--cc=tglx@linutronix.de \
--cc=torvalds@linux-foundation.org \
--cc=viresh.kumar@linaro.org \
--cc=viro@zeniv.linux.org.uk \
--cc=willy@infradead.org \
--cc=x86@kernel.org \
--cc=zenglg.jy@cn.fujitsu.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).