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

commit 9bf148cb0812595bfdf5100bd2c07e9bec9c6ef5 upstream.

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: fcc7ffd67991 "x86, mpx: Decode MPX instruction to get bound violation information"
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Acked-by: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>
Link: http://lkml.kernel.org/r/1456512931-3388-1-git-send-email-colin.king@canonical.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/x86/mm/mpx.c b/arch/x86/mm/mpx.c
index b2fd67da1701433d9168ebf1d0a908330544bd7d..ef05755a190063cdf79210f7ac164aef1a0f4ec5 100644 (file)
--- a/arch/x86/mm/mpx.c
+++ b/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;
        }