msm: perf: Protect buffer overflow due to malicious user

In function krait_pmu_disable_event, parameter hwc comes from
userspace and is untrusted.The function krait_clearpmu is called
after the function get_krait_evtinfo.
Function get_krait_evtinfo as parameter krait_evt_type variable
which is used to extract the groupcode(reg) which is bound to
 KRAIT_MAX_L1_REG (is 3). After validation,one code path modifies
groupcode(reg):If this code path executes, groupcode(reg) can be
3,4, 5, or 6. In krait_clearpmu groupcode used to access array
krait_functions whose size is 3. Since groupcode can be 3,4,5,6
accessing array krait_functions lead to bufferoverlflow.
This change will validate groupcode not to exceed 3.

Change-Id: I48c92adda137d8a074b4e1a367a468195a810ca1
CRs-fixed: 962450
Signed-off-by: Swetha Chikkaboraiah <schikk@codeaurora.org>

arch/arm/kernel/perf_event_msm_krait.c

 /*
- * Copyright (c) 2011-2014, The Linux Foundation. All rights reserved.
+ * Copyright (c) 2011-2014, 2016 The Linux Foundation. All rights reserved.
  *
  * This program is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 2 and
@@ -208,9 +208,6 @@ static unsigned int get_krait_evtinfo(unsigned int krait_evt_type,
 	code = (krait_evt_type & 0x00FF0) >> 4;
 	group = krait_evt_type & 0x0000F;
 
-	if ((group > 3) || (reg > KRAIT_MAX_L1_REG))
-		return -EINVAL;
-
 	if (prefix != KRAIT_EVT_PREFIX && prefix != KRAIT_VENUMEVT_PREFIX)
 		return -EINVAL;
 
@@ -221,6 +218,9 @@ static unsigned int get_krait_evtinfo(unsigned int krait_evt_type,
 			reg += VENUM_BASE_OFFSET;
 	}
 
+	if ((group > 3) || (reg > KRAIT_MAX_L1_REG))
+		return -EINVAL;
+
 	evtinfo->group_setval = 0x80000000 | (code << (group * 8));
 	evtinfo->groupcode = reg;
 	evtinfo->armv7_evt_type = evt_type_base[reg] | group;