Commit b80328be authored Aug 01, 2017 by Eric W. Biederman

signal/metag: 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
hat 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.

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 Hogan <james.hogan@imgtec.com>
Cc: linux-metag@vger.kernel.org
Ref: ac919f08 ("metag: Traps")
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>

parent b5daf2b9

arch/metag/include/uapi/asm/siginfo.h

+7 −0

Original line number	Diff line number	Diff line
		@@ -6,4 +6,11 @@

		#include <asm-generic/siginfo.h>

		/*
		* SIGFPE si_codes
		*/
		#ifdef __KERNEL__
		#define FPE_FIXME 0 /* Broken dup of SI_USER */
		#endif /* __KERNEL__ */

		#endif

arch/metag/kernel/traps.c

+1 −1

Original line number	Diff line number	Diff line
		@@ -735,7 +735,7 @@ TBIRES fpe_handler(TBIRES State, int SigNum, int Triggers, int Inst, PTBI pTBI)
		else if (error_state & TXSTAT_FPE_INEXACT_BIT)
		info.si_code = FPE_FLTRES;
		else
		info.si_code = 0;
		info.si_code = FPE_FIXME;
		info.si_errno = 0;
		info.si_addr = (__force void __user *)regs->ctx.CurrPC;
		force_sig_info(SIGFPE, &info, current);