32-on-64 (x86-64) siginfo corruption

32-on-64 (x86-64) siginfo corruption

[Albert Cahalan]

The situation:  32-bit debugger, 32-bit child, 64-bit kernel

The debugger sends an RT signal to the child. (to stop it, with
a queue and siginfo so that non-debugger signals don't get lost)
To do this, the debugger uses tgkill().

Later, the debugger checks the child's siginfo_t before discarding
it. This is to be sure that the child didn't get the RT signal from
some other source. The debugger fills a siginfo_t with 0xff, then
fetches siginfo data via ptrace. The data is corrupt:

FIELD     32-ON-64   NORMAL
si_pid      -1       getpid()
si_uid    getpid()   getuid()

The "getpid" and "getuid" above are done in the debugger, not in
the child. The si_code values are SI_TKILL.

Probably the other ports with 32-on-64 support ought to verify
that this stuff works right.

Re: 32-on-64 (x86-64) siginfo corruption

[David S. Miller]

From: "Albert Cahalan" <acahalan@gmail.com>
Date: Wed, 5 Apr 2006 23:20:07 -0400

> The situation:  32-bit debugger, 32-bit child, 64-bit kernel
> 
> The debugger sends an RT signal to the child. (to stop it, with
> a queue and siginfo so that non-debugger signals don't get lost)
> To do this, the debugger uses tgkill().
> 
> Later, the debugger checks the child's siginfo_t before discarding
> it. This is to be sure that the child didn't get the RT signal from
> some other source. The debugger fills a siginfo_t with 0xff, then
> fetches siginfo data via ptrace. The data is corrupt:
> 
> FIELD     32-ON-64   NORMAL
> si_pid      -1       getpid()
> si_uid    getpid()   getuid()
> 
> The "getpid" and "getuid" above are done in the debugger, not in
> the child. The si_code values are SI_TKILL.
> 
> Probably the other ports with 32-on-64 support ought to verify
> that this stuff works right.

Ugh, just like PTRACE_GETEVENTMSG we'll need translations for
GETSIGINFO and SETSIGINFO.

I've CC'd linux-arch which is where the port maintainers hang
out and look for postings about issues like this.  I mentioned
the PTRACE_GETEVENTMSG issue there just the other day.