x86/ptrace: Remove checks for TIF_IA32 when changing CS and SS

The ability for modified CS and/or SS to be useful has nothing
to do with TIF_IA32.  Similarly, if there's an exploit involving
changing CS or SS, it's exploitable with or without a TIF_IA32
check.

So just delete the check.

Signed-off-by: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Link: http://lkml.kernel.org/r/71c7ab36456855d11ae07edd4945a7dfe80f9915.1424822291.git.luto@amacapital.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>

arch/x86/kernel/ptrace.c

@@ -364,18 +364,12 @@ static int set_segment_reg(struct task_struct *task,
 	case offsetof(struct user_regs_struct,cs):
 		if (unlikely(value == 0))
 			return -EIO;
-#ifdef CONFIG_IA32_EMULATION
+		task_pt_regs(task)->cs = value;
-		if (test_tsk_thread_flag(task, TIF_IA32))
-			task_pt_regs(task)->cs = value;
-#endif
 		break;
 	case offsetof(struct user_regs_struct,ss):
 		if (unlikely(value == 0))
 			return -EIO;
-#ifdef CONFIG_IA32_EMULATION
+		task_pt_regs(task)->ss = value;
-		if (test_tsk_thread_flag(task, TIF_IA32))
-			task_pt_regs(task)->ss = value;
-#endif
 		break;
 	}