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signal/parisc: Document a conflict with SI_USER with SIGFPE 

Setting si_code to 0 results in a userspace seeing an si_code of 0.
This is the same si_code as SI_USER.  Posix and common sense requires
that SI_USER not be a signal specific si_code.  As such this use of 0
for the si_code is a pretty horribly broken ABI.

Further use of si_code == 0 guaranteed that copy_siginfo_to_user saw a
value of __SI_KILL and now sees a value of SIL_KILL with the result
that uid and pid fields are copied and which might copying the si_addr
field by accident but certainly not by design.  Making this a very
flakey implementation.

Utilizing FPE_FIXME siginfo_layout will now return SIL_FAULT and the
appropriate fields will reliably be copied.

This bug is 13 years old and parsic machines are no longer being built
so I don't know if it possible or worth fixing it.  But it is at least
worth documenting this so other architectures don't make the same
mistake.

Possible ABI fixes includee:
  - Send the signal without siginfo
  - Don't generate a signal
  - Possibly assign and use an appropriate si_code
  - Don't handle cases which can't happen

Cc: "James E.J. Bottomley" <jejb@parisc-linux.org>
Cc: Helge Deller <deller@gmx.de>
Cc: linux-parisc@vger.kernel.org
Ref: 313c01d3e3fd ("[PATCH] PA-RISC update for 2.6.0")
Histroy Tree: https://git.kernel.org/pub/scm/linux/kernel/git/tglx/history.git
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
This commit is contained in:
Eric W. Biederman 2017-07-31 22:25:01 -05:00
parent 500d583005
commit b5daf2b9d1
2 changed files with 8 additions and 1 deletions
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7
arch/parisc/include/uapi/asm/siginfo.h
View File

@ -8,4 +8,11 @@
#include <asm-generic/siginfo.h>
/*
* SIGFPE si_codes
*/
#ifdef __KERNEL__
#define FPE_FIXME 0 /* Broken dup of SI_USER */
#endif /* __KERNEL__ */
#endif

2
arch/parisc/kernel/traps.c
View File

@ -629,7 +629,7 @@ void notrace handle_interruption(int code, struct pt_regs *regs)
si.si_signo = SIGFPE;
/* Set to zero, and let the userspace app figure it out from
the insn pointed to by si_addr */
si.si_code = 0;
si.si_code = FPE_FIXME;
si.si_addr = (void __user *) regs->iaoq[0];
force_sig_info(SIGFPE, &si, current);
return;