ARM: 7526/1: traps: send SIGILL if get_user fails on undef handling path

get_user may fail to load from the provided __user address due to an
unhandled fault generated by the access.

In the case of the undefined instruction trap, this results in failure
to load the faulting instruction, in which case we should send SIGILL to
the task rather than continue with potentially uninitialised data.
Signed-off-by: NWill Deacon <will.deacon@arm.com>
Cc: stable@vger.kernel.org
Signed-off-by: NRussell King <rmk+kernel@arm.linux.org.uk>

arch/arm/kernel/traps.c

@@ -420,20 +420,23 @@ asmlinkage void __exception do_undefinstr(struct pt_regs *regs)
 #endif
 			instr = *(u32 *) pc;
 	} else if (thumb_mode(regs)) {
-		get_user(instr, (u16 __user *)pc);
+		if (get_user(instr, (u16 __user *)pc))
+			goto die_sig;
 		if (is_wide_instruction(instr)) {
 			unsigned int instr2;
-			get_user(instr2, (u16 __user *)pc+1);
+			if (get_user(instr2, (u16 __user *)pc+1))
+				goto die_sig;
 			instr <<= 16;
 			instr |= instr2;
 		}
-	} else {
-		get_user(instr, (u32 __user *)pc);
+	} else if (get_user(instr, (u32 __user *)pc)) {
+		goto die_sig;
 	}
 
 	if (call_undef_hook(regs, instr) == 0)
 		return;
 
+die_sig:
 #ifdef CONFIG_DEBUG_USER
 	if (user_debug & UDBG_UNDEFINED) {
 		printk(KERN_INFO "%s (%d): undefined instruction: pc=%p\n",