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Re: [PATCH v2 00/20] Fix handling of compat_siginfo_t

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On Wed, Nov 4, 2015 at 4:50 PM, Amanieu d'Antras <amanieu@gmail.com> wrote:
> One issue that isn't resolved in this series is sending signals between a 32-bit
> process and 64-bit process. Sending a si_int will work correctly, but a si_ptr
> value will likely get corrupted due to the different layouts of the 32-bit and
> 64-bit siginfo_t structures.

This is so screwed up it's not even funny.

A 64-bit big-endian compat calls rt_sigqueueinfo.  It passes in (among
other things) a sigval_t.  The kernel can choose to interpret it as a
pointer (call it p) or an integer (call it i).  Then (unsigned long)p
= (i<<32) | [something].  If the number was an integer to begin with
*and* user code zeroed out the mess first, then [something] will be 0.
Regardless, p != i unless they're both zero.

If the result gets delivered to a signalfd, then it's plausible that
everything could work.  If it gets delivered to a 64-bit siginfo, then
all is well because it's in exactly the same screwed up state it was
in when the signal gets sent.

If, however, it's delivered to a compat task, wtf is the kernel
supposed to do?  We're effectively supposed to convert a 64-bit
sigval_t to a 32-bit sigval_t.  On a little-endian architecture, we
can fudge it because it doesn't really matter whether we consider the
pointer or the int to be authoritative.  I think that, on big-endian,
we're screwed.

BTW, x86 has its own set of screwups here.  Somehow cr2 and error_code
ended up as part of ucontext instead of siginfo, which makes
absolutely no sense to me and bloats task_struct.

--Andy
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[PATCH v2 00/20] Fix handling of compat_siginfo_t Amanieu d'Antras <amanieu@gmail.com> - 2015-11-05 02:00 +0100
  [PATCH v2 14/20] powerpc: Use generic copy_siginfo_{to,from}_user32 Amanieu d'Antras <amanieu@gmail.com> - 2015-11-05 02:00 +0100
  [PATCH v2 04/20] x86: Rewrite copy_siginfo_{to,from}_user32 Amanieu d'Antras <amanieu@gmail.com> - 2015-11-05 02:00 +0100
    Re: [PATCH v2 04/20] x86: Rewrite copy_siginfo_{to,from}_user32 "H. Peter Anvin" <hpa@zytor.com> - 2015-11-05 03:40 +0100
  [PATCH v2 05/20] mips: Clean up compat_siginfo_t Amanieu d'Antras <amanieu@gmail.com> - 2015-11-05 02:00 +0100
  [PATCH v2 06/20] mips: Use generic copy_siginfo_{to,from}_user32 Amanieu d'Antras <amanieu@gmail.com> - 2015-11-05 02:00 +0100
  [PATCH v2 19/20] signalfd: Fix some issues in signalfd_copyinfo Amanieu d'Antras <amanieu@gmail.com> - 2015-11-05 02:00 +0100
  [PATCH v2 11/20] s390: Use generic compat_siginfo_t Amanieu d'Antras <amanieu@gmail.com> - 2015-11-05 02:00 +0100
  [PATCH v2 10/20] parsic: Use generic copy_siginfo_{to,from}_user32 Amanieu d'Antras <amanieu@gmail.com> - 2015-11-05 02:00 +0100
  [PATCH v2 17/20] sparc: Use generic compat_siginfo_t Amanieu d'Antras <amanieu@gmail.com> - 2015-11-05 02:00 +0100
  [PATCH v2 18/20] sparc: Use generic copy_siginfo_{to,from}_user32 Amanieu d'Antras <amanieu@gmail.com> - 2015-11-05 02:00 +0100
  [PATCH v2 03/20] x86: Update compat_siginfo_t to be closer to the generic version Amanieu d'Antras <amanieu@gmail.com> - 2015-11-05 02:00 +0100
  [PATCH v2 20/20] signal: Remove unnecessary zero-initialization of siginfo_t Amanieu d'Antras <amanieu@gmail.com> - 2015-11-05 02:00 +0100
  [PATCH v2 02/20] compat: Add generic copy_siginfo_{to,from}_user32 Amanieu d'Antras <amanieu@gmail.com> - 2015-11-05 02:00 +0100
  [PATCH v2 16/20] tile: Use generic copy_siginfo_{to,from}_user32 Amanieu d'Antras <amanieu@gmail.com> - 2015-11-05 02:00 +0100
  [PATCH v2 07/20] arm64: Use generic compat_siginfo_t Amanieu d'Antras <amanieu@gmail.com> - 2015-11-05 02:00 +0100
  [PATCH v2 01/20] compat: Add generic compat_siginfo_t Amanieu d'Antras <amanieu@gmail.com> - 2015-11-05 02:00 +0100
  Re: [PATCH v2 00/20] Fix handling of compat_siginfo_t Andy Lutomirski <luto@amacapital.net> - 2015-11-08 06:10 +0100
    Re: [PATCH v2 00/20] Fix handling of compat_siginfo_t Oleg Nesterov <oleg@redhat.com> - 2015-11-09 15:20 +0100

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