parisc: Ensure userspace privilege for ptraced processes in regset functions

On parisc the privilege level of a process is stored in the lowest two bits of the instruction pointers (IAOQ0 and IAOQ1). On Linux we use privilege level 0 for the kernel and privilege level 3 for user-space. So userspace should not be allowed to modify IAOQ0 or IAOQ1 of a ptraced process to change it's privilege level to e.g. 0 to try to gain kernel privileges.

This patch prevents such modifications in the regset support functions by always setting the two lowest bits to one (which relates to privilege level 3 for user-space) if IAOQ0 or IAOQ1 are modified via ptrace regset calls.

index c60229075a33..4fa0d4c07521 100644
@@ -502,7 +510,8 @@ static void set_reg(struct pt_regs *regs, int num, unsigned long val)
 			return;
 	case RI(iaoq[0]):
 	case RI(iaoq[1]):
-			regs->iaoq[num - RI(iaoq[0])] = val;
+			/* set 2 lowest bits to ensure userspace privilege: */
+			regs->iaoq[num - RI(iaoq[0])] = val | 3;
 			return;
 	case RI(sar):	regs->sar = val;
 			return;