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Re: [x86] 45fc8757d1: BUG:unable_to_handle_kernel

From Linus Torvalds <torvalds@linux-foundation.org>
Newsgroups linux.kernel
Subject Re: [x86] 45fc8757d1: BUG:unable_to_handle_kernel
Date 2017-03-17 22:20 +0100
Message-ID <tm7rY-495-1@gated-at.bofh.it> (permalink)
References (2 earlier) <tm4u5-21N-5@gated-at.bofh.it> <tm4u6-21N-25@gated-at.bofh.it> <tm4Ns-29P-21@gated-at.bofh.it> <tm6vT-3sM-7@gated-at.bofh.it> <tm6vT-3sM-5@gated-at.bofh.it>
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On Fri, Mar 17, 2017 at 1:18 PM, Andy Lutomirski <luto@amacapital.net> wrote:
> On Fri, Mar 17, 2017 at 12:36 PM, Linus Torvalds
> <torvalds@linux-foundation.org> wrote:
>>
>> Can they even *read* the LDT contents, though? The whole accessed bit
>> doesn't show up in 'struct user_desc', so you can neither set it nor
>> read it.
>
> LAR.  I've learned to never underestimate the absurdity of the games
> played by 16-bit apps.  (See, for example, the fact that some of them
> apparently use SGDT just to find a page that's guaranteed not to be
> accessible.)

Ugh. Right you are, LAR will return those type bits.

Of course, maybe somebody cares about them in the GDT already?  So
it's visible even with your patch, isn't it. We give users four
entries to play with...

                Linus

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Re: [x86] 45fc8757d1: BUG:unable_to_handle_kernel Linus Torvalds <torvalds@linux-foundation.org> - 2017-03-17 19:00 +0100
  Re: [x86] 45fc8757d1: BUG:unable_to_handle_kernel Linus Torvalds <torvalds@linux-foundation.org> - 2017-03-17 19:10 +0100
    Re: [x86] 45fc8757d1: BUG:unable_to_handle_kernel Linus Torvalds <torvalds@linux-foundation.org> - 2017-03-17 19:10 +0100
      Re: [x86] 45fc8757d1: BUG:unable_to_handle_kernel Andy Lutomirski <luto@kernel.org> - 2017-03-17 19:30 +0100
        Re: [x86] 45fc8757d1: BUG:unable_to_handle_kernel Andy Lutomirski <luto@amacapital.net> - 2017-03-17 21:20 +0100
          Re: [x86] 45fc8757d1: BUG:unable_to_handle_kernel Linus Torvalds <torvalds@linux-foundation.org> - 2017-03-17 22:20 +0100
        Re: [x86] 45fc8757d1: BUG:unable_to_handle_kernel Linus Torvalds <torvalds@linux-foundation.org> - 2017-03-17 22:50 +0100

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