[tip:x86/urgent] x86/signal: Remove bogus user_64bit_mode() check from sigaction_compat_abi()

[tip-bot for Dmitry Safonov <tipbot@zytor.com>]

Commit-ID:  3b68db0c1f80c763213f07db60b4feda186345f5
Gitweb:     http://git.kernel.org/tip/3b68db0c1f80c763213f07db60b4feda186345f5
Author:     Dmitry Safonov <0x7f454c46@gmail.com>
AuthorDate: Thu, 20 Oct 2016 00:53:08 +0300
Committer:  Thomas Gleixner <tglx@linutronix.de>
CommitDate: Thu, 20 Oct 2016 11:17:12 +0200

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 64bit 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 64bit 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 64bit mode.

[ tglx: Rewrote changelog ]

Fixes: 6846351052e6 ("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.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
 arch/x86/kernel/signal_compat.c | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/arch/x86/kernel/signal_compat.c b/arch/x86/kernel/signal_compat.c
index 40df337..ec1f756 100644
--- a/arch/x86/kernel/signal_compat.c
+++ b/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())