x86/signal: Remove bogus user_64bit_mode() check from sigaction_compat_abi()

The recent introduction of SA_X32/IA32 sa_flags added a check for
user_64bit_mode() into sigaction_compat_abi(). user_64bit_mode() is true
for native 64-bit processes and x32 processes.

Due to that the function returns w/o setting the SA_X32_ABI flag for X32
processes. In consequence the kernel attempts to deliver the signal to the
X32 process in native 64-bit mode causing the process to segfault.

Remove the check, so the actual check for X32 mode which sets the ABI flag
can be reached. There is no side effect for native 64-bit mode.

[ tglx: Rewrote changelog ]

Fixes: 68463510 ("x86/signal: Add SA_{X32,IA32}_ABI sa_flags")
Reported-by: Mikulas Patocka <mpatocka@redhat.com>
Tested-by: Adam Borowski <kilobyte@angband.pl>
Signed-off-by: Dmitry Safonov <0x7f454c46@gmail.com>
Cc: Dmitry Safonov <dsafonov@virtuozzo.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: linux-mm@kvack.org
Cc: Cyrill Gorcunov <gorcunov@openvz.org>
Cc: Pavel Emelyanov <xemul@virtuozzo.com>
Link: http://lkml.kernel.org/r/CAJwJo6Z8ZWPqNfT6t-i8GW1MKxQrKDUagQqnZ%2B0%2B697%3DMyVeGg@mail.gmail.comSigned-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>

arch/x86/kernel/signal_compat.c

@@ -105,9 +105,6 @@ void sigaction_compat_abi(struct k_sigaction *act, struct k_sigaction *oact)
 	/* Don't let flags to be set from userspace */
 	act->sa.sa_flags &= ~(SA_IA32_ABI | SA_X32_ABI);
 
-	if (user_64bit_mode(current_pt_regs()))
-		return;
-
 	if (in_ia32_syscall())
 		act->sa.sa_flags |= SA_IA32_ABI;
 	if (in_x32_syscall())