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Re: Rethinking sigcontext's xfeatures slightly for PKRU's benefit?

From Andy Lutomirski <luto@amacapital.net>
Newsgroups linux.kernel
Subject Re: Rethinking sigcontext's xfeatures slightly for PKRU's benefit?
Date 2015-12-18 20:30 +0100
Message-ID <qH8T0-1js-7@gated-at.bofh.it> (permalink)
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On Fri, Dec 18, 2015 at 10:42 AM, Dave Hansen
<dave.hansen@linux.intel.com> wrote:
> On 12/18/2015 08:04 AM, Andy Lutomirski wrote:
>> 1b. If the app malfunctions such that RSP points to pmem, the kernel
>> MUST NOT clobber the pmem space.  I think that this basically mandates
>> that PKRU needs to have some safe state (i.e. definitely not the init
>> state) on signal delivery: the kernel is going to write a signal frame
>> at the address identified by RSP, and that address is in pmem, so
>> those writes need to fail.
>
> The kernel is writing the signal frame using normal old copy_to_user().
>  Those are writing through mappings with _PAGE_USER set and should be
> subject to the PKRU state of the thread before the signal started to be
> delivered.
>
> We don't do the fpu__clear() until after this copy, so I think pkeys
> enforcement is being done properly for this today.

True, but I think only in a very limited sense.  Your average signal
handler is reasonably like to execute "push $rbp" as its very first
instruction, at which point we're immediately screwed with the current
arrangement.

--Andy

-- 
Andy Lutomirski
AMA Capital Management, LLC
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Thread

Rethinking sigcontext's xfeatures slightly for PKRU's benefit? Andy Lutomirski <luto@kernel.org> - 2015-12-18 02:50 +0100
  Re: Rethinking sigcontext's xfeatures slightly for PKRU's benefit? Dave Hansen <dave.hansen@linux.intel.com> - 2015-12-18 03:20 +0100
    Re: Rethinking sigcontext's xfeatures slightly for PKRU's benefit? Andy Lutomirski <luto@amacapital.net> - 2015-12-18 03:40 +0100
      Re: Rethinking sigcontext's xfeatures slightly for PKRU's benefit? Dave Hansen <dave.hansen@linux.intel.com> - 2015-12-18 04:00 +0100
        Re: Rethinking sigcontext's xfeatures slightly for PKRU's benefit? Andy Lutomirski <luto@amacapital.net> - 2015-12-18 06:30 +0100
          Re: Rethinking sigcontext's xfeatures slightly for PKRU's benefit? "H. Peter Anvin" <hpa@zytor.com> - 2015-12-18 07:50 +0100
            Re: Rethinking sigcontext's xfeatures slightly for PKRU's benefit? Andy Lutomirski <luto@amacapital.net> - 2015-12-18 17:10 +0100
              Re: Rethinking sigcontext's xfeatures slightly for PKRU's benefit? Dave Hansen <dave.hansen@linux.intel.com> - 2015-12-18 18:00 +0100
              Re: Rethinking sigcontext's xfeatures slightly for PKRU's benefit? Dave Hansen <dave.hansen@linux.intel.com> - 2015-12-18 19:50 +0100
                Re: Rethinking sigcontext's xfeatures slightly for PKRU's benefit? Andy Lutomirski <luto@amacapital.net> - 2015-12-18 20:30 +0100
                Re: Rethinking sigcontext's xfeatures slightly for PKRU's benefit? Dave Hansen <dave.hansen@linux.intel.com> - 2015-12-18 21:10 +0100
                Re: Rethinking sigcontext's xfeatures slightly for PKRU's benefit? Andy Lutomirski <luto@amacapital.net> - 2015-12-18 21:30 +0100
                Re: Rethinking sigcontext's xfeatures slightly for PKRU's benefit? Linus Torvalds <torvalds@linux-foundation.org> - 2015-12-18 21:40 +0100
                Re: Rethinking sigcontext's xfeatures slightly for PKRU's benefit? Andy Lutomirski <luto@amacapital.net> - 2015-12-18 21:50 +0100
                Re: Rethinking sigcontext's xfeatures slightly for PKRU's benefit? "H. Peter Anvin" <hpa@zytor.com> - 2015-12-18 22:00 +0100
                Re: Rethinking sigcontext's xfeatures slightly for PKRU's benefit? Andy Lutomirski <luto@amacapital.net> - 2015-12-18 22:10 +0100
                Re: Rethinking sigcontext's xfeatures slightly for PKRU's benefit? Dave Hansen <dave.hansen@linux.intel.com> - 2015-12-18 22:10 +0100
                Re: Rethinking sigcontext's xfeatures slightly for PKRU's benefit? Linus Torvalds <torvalds@linux-foundation.org> - 2015-12-18 22:10 +0100
                Re: Rethinking sigcontext's xfeatures slightly for PKRU's benefit? Dave Hansen <dave.hansen@linux.intel.com> - 2015-12-18 22:20 +0100
                Re: Rethinking sigcontext's xfeatures slightly for PKRU's benefit? Linus Torvalds <torvalds@linux-foundation.org> - 2015-12-18 22:50 +0100
                Re: Rethinking sigcontext's xfeatures slightly for PKRU's benefit? Andy Lutomirski <luto@amacapital.net> - 2015-12-18 23:30 +0100
                Re: Rethinking sigcontext's xfeatures slightly for PKRU's benefit? Linus Torvalds <torvalds@linux-foundation.org> - 2015-12-19 00:10 +0100
                Re: Rethinking sigcontext's xfeatures slightly for PKRU's benefit? Andy Lutomirski <luto@amacapital.net> - 2015-12-19 00:20 +0100
                Re: Rethinking sigcontext's xfeatures slightly for PKRU's benefit? Linus Torvalds <torvalds@linux-foundation.org> - 2015-12-19 00:30 +0100
                Re: Rethinking sigcontext's xfeatures slightly for PKRU's benefit? Dave Hansen <dave.hansen@linux.intel.com> - 2015-12-21 18:10 +0100
                Re: Rethinking sigcontext's xfeatures slightly for PKRU's benefit? Andy Lutomirski <luto@amacapital.net> - 2015-12-22 00:00 +0100
                Re: Rethinking sigcontext's xfeatures slightly for PKRU's benefit? Dave Hansen <dave.hansen@linux.intel.com> - 2015-12-22 00:10 +0100
                Re: Rethinking sigcontext's xfeatures slightly for PKRU's benefit? Andy Lutomirski <luto@amacapital.net> - 2015-12-22 00:10 +0100
                Re: Rethinking sigcontext's xfeatures slightly for PKRU's benefit? Dave Hansen <dave.hansen@linux.intel.com> - 2015-12-22 00:10 +0100
                Re: Rethinking sigcontext's xfeatures slightly for PKRU's benefit? Dave Hansen <dave.hansen@linux.intel.com> - 2015-12-22 00:10 +0100
                Re: Rethinking sigcontext's xfeatures slightly for PKRU's benefit? Andy Lutomirski <luto@amacapital.net> - 2015-12-22 00:10 +0100
                Re: Rethinking sigcontext's xfeatures slightly for PKRU's benefit? Dave Hansen <dave.hansen@linux.intel.com> - 2015-12-30 00:50 +0100
                Re: Rethinking sigcontext's xfeatures slightly for PKRU's benefit? Linus Torvalds <torvalds@linux-foundation.org> - 2015-12-18 22:20 +0100
          Re: Rethinking sigcontext's xfeatures slightly for PKRU's benefit? Ingo Molnar <mingo@kernel.org> - 2015-12-18 09:40 +0100
  Re: Rethinking sigcontext's xfeatures slightly for PKRU's benefit? Christoph Hellwig <hch@infradead.org> - 2015-12-18 10:00 +0100
    Re: Rethinking sigcontext's xfeatures slightly for PKRU's benefit? Borislav Petkov <bp@alien8.de> - 2015-12-18 14:00 +0100

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