x86/mpx: Fix off-by-one comparison with nr_registers

In the unlikely event that regno == nr_registers then we get an array
overrun on regoff because the invalid register check is currently
off-by-one. Fix this with a check that regno is >= nr_registers instead.

Detected with static analysis using CoverityScan.

Fixes: fcc7ffd "x86, mpx: Decode MPX instruction to get bound violation information"
Signed-off-by: Colin Ian King <[email protected]>
Acked-by: Dave Hansen <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: "Kirill A . Shutemov" <[email protected]>
Cc: [email protected]
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Thomas Gleixner <[email protected]>

arch/x86/mm/mpx.c

@@ -123,7 +123,7 @@ static int get_reg_offset(struct insn *insn, struct pt_regs *regs,
 		break;
 	}
 
-	if (regno > nr_registers) {
+	if (regno >= nr_registers) {
 		WARN_ONCE(1, "decoded an instruction with an invalid register");
 		return -EINVAL;
 	}