x86/asm/entry, perf: Fix incorrect TIF_IA32 check in code_segment_base()

We want to check whether user code is in 32-bit mode, not
whether the task is nominally 32-bit.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brad Spengler <spender@grsecurity.net>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/33e5107085ce347a8303560302b15c2cadd62c4c.1426728647.git.luto@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

arch/x86/kernel/cpu/perf_event.c

@@ -2161,10 +2161,9 @@ static unsigned long code_segment_base(struct pt_regs *regs)
 	if (user_mode(regs) && regs->cs != __USER_CS)
 		return get_segment_base(regs->cs);
 #else
-	if (test_thread_flag(TIF_IA32)) {
-		if (user_mode(regs) && regs->cs != __USER32_CS)
+	if (user_mode(regs) && !user_64bit_mode(regs) &&
+	    regs->cs != __USER32_CS)
 		return get_segment_base(regs->cs);
-	}
 #endif
 	return 0;
 }