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Re: BUG: unable to handle kernel paging request from pty_write [was: Linux 4.4.2]

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On 02/26/2016 10:05 AM, Linus Torvalds wrote:
> On Fri, Feb 26, 2016 at 9:52 AM, Peter Hurley <peter@hurleysoftware.com> wrote:
>>
>> So more analysis would seem to confirm that RSP has been bumped +8
>> while in ttwu_stat() so when the epilog executed, register restore
>> was off by 1 qword. However, there's nothing in ttwu_stat() that
>> results in stack pointer offset by +1 qword from prolog.
> 
> I agree.
> 
> That's why I'm actually starting to suspect that it's an AMD microcode
> bug that we know very little about. There's apparently register
> corruption (the guess being from NMI handling, but virtualization was
> also involved) under some circumstances.

Yep, that could explain it.

> Of course, if Jiri isn't actually running this on an AMD CPU, that
> theory flies right out the window.

I'll wait for Jiri to confirm before sinking more time here.


> But we do have a reported oops on
> the security list that looks totally different in the big picture, but
> shares the exact same "corrupted stack pointer register state
> resulting in crazy instruction pointer, resulting in NX fault"
> behavior in the end.
> 
> In the other case, microcode patchlevel 0x0600081c was fine, and
> 0x06000832 is the one exhibiting the corruption problem.
> 
> I've contacted Robert Święcki (who found the microcode problem) in
> case he wants to weigh in in this thread.. He was talking to some AMD
> people, but I don't know the exactly who.

Ok, thanks for the info.

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Re: BUG: unable to handle kernel paging request from pty_write [was:  Linux 4.4.2] Linus Torvalds <torvalds@linux-foundation.org> - 2016-02-26 19:10 +0100
  Re: BUG: unable to handle kernel paging request from pty_write [was:  Linux 4.4.2] Peter Hurley <peter@hurleysoftware.com> - 2016-02-26 19:20 +0100
  Re: BUG: unable to handle kernel paging request from pty_write [was:  Linux 4.4.2] Borislav Petkov <bp@alien8.de> - 2016-02-26 19:20 +0100
  Re: BUG: unable to handle kernel paging request from pty_write [was:  Linux 4.4.2] Linus Torvalds <torvalds@linux-foundation.org> - 2016-02-26 20:50 +0100
    Re: BUG: unable to handle kernel paging request from pty_write [was:  Linux 4.4.2] Robert Święcki <robert@swiecki.net> - 2016-02-26 21:10 +0100
      Re: BUG: unable to handle kernel paging request from pty_write [was:  Linux 4.4.2] Jiri Slaby <jslaby@suse.cz> - 2016-02-29 08:40 +0100
        Re: BUG: unable to handle kernel paging request from pty_write [was:  Linux 4.4.2] Henrique de Moraes Holschuh <hmh@hmh.eng.br> - 2016-02-29 13:50 +0100

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