From: Alexei Fedorov <Alexei.Fedorov@arm.com>
Date: Fri, 24 May 2019 11:17:09 +0000 (+0100)
Subject: Add support for Branch Target Identification
X-Git-Url: http://git.lede-project.org./?a=commitdiff_plain;h=9fc59639e649f614318f78ae2ca103fe102405ec;p=project%2Fbcm63xx%2Fatf.git

Add support for Branch Target Identification

This patch adds the functionality needed for platforms to provide
Branch Target Identification (BTI) extension, introduced to AArch64
in Armv8.5-A by adding BTI instruction used to mark valid targets
for indirect branches. The patch sets new GP bit [50] to the stage 1
Translation Table Block and Page entries to denote guarded EL3 code
pages which will cause processor to trap instructions in protected
pages trying to perform an indirect branch to any instruction other
than BTI.
BTI feature is selected by BRANCH_PROTECTION option which supersedes
the previous ENABLE_PAUTH used for Armv8.3-A Pointer Authentication
and is disabled by default. Enabling BTI requires compiler support
and was tested with GCC versions 9.0.0, 9.0.1 and 10.0.0.
The assembly macros and helpers are modified to accommodate the BTI
instruction.
This is an experimental feature.
Note. The previous ENABLE_PAUTH build option to enable PAuth in EL3
is now made as an internal flag and BRANCH_PROTECTION flag should be
used instead to enable Pointer Authentication.
Note. USE_LIBROM=1 option is currently not supported.

Change-Id: Ifaf4438609b16647dc79468b70cd1f47a623362e
Signed-off-by: Alexei Fedorov <Alexei.Fedorov@arm.com>
---

diff --git a/Makefile b/Makefile
index 976f514d..1078ef53 100644
--- a/Makefile
+++ b/Makefile
@@ -117,6 +117,29 @@ ifneq (${GENERATE_COT},0)
         FWU_FIP_DEPS += fwu_certificates
 endif
 
+# Process BRANCH_PROTECTION value and set
+# Pointer Authentication and Branch Target Identification flags
+ifeq (${BRANCH_PROTECTION},0)
+	# Default value turns off all types of branch protection
+	BP_OPTION := none
+else ifneq (${ARCH},aarch64)
+        $(error BRANCH_PROTECTION requires AArch64)
+else ifeq (${BRANCH_PROTECTION},1)
+	# Enables all types of branch protection features
+	BP_OPTION := standard
+	ENABLE_BTI := 1
+	ENABLE_PAUTH := 1
+else ifeq (${BRANCH_PROTECTION},2)
+	# Return address signing to its standard level
+	BP_OPTION := pac-ret
+	ENABLE_PAUTH := 1
+else ifeq (${BRANCH_PROTECTION},3)
+	# Extend the signing to include leaf functions
+	BP_OPTION := pac-ret+leaf
+	ENABLE_PAUTH := 1
+else
+        $(error Unknown BRANCH_PROTECTION value ${BRANCH_PROTECTION})
+endif
 
 ################################################################################
 # Toolchain
@@ -189,6 +212,10 @@ endif
 TF_CFLAGS_aarch32	+=	-mno-unaligned-access
 TF_CFLAGS_aarch64	+=	-mgeneral-regs-only -mstrict-align
 
+ifneq (${BP_OPTION},none)
+TF_CFLAGS_aarch64	+=	-mbranch-protection=${BP_OPTION}
+endif
+
 ASFLAGS_aarch32		=	$(march32-directive)
 ASFLAGS_aarch64		=	$(march64-directive)
 
@@ -451,26 +478,30 @@ ifeq ($(DYN_DISABLE_AUTH), 1)
 endif
 
 # If pointer authentication is used in the firmware, make sure that all the
-# registers associated to it are also saved and restored. Not doing it would
-# leak the value of the key used by EL3 to EL1 and S-EL1.
+# registers associated to it are also saved and restored.
+# Not doing it would leak the value of the keys used by EL3 to EL1 and S-EL1.
 ifeq ($(ENABLE_PAUTH),1)
-    ifneq ($(ARCH),aarch64)
-        $(error ENABLE_PAUTH=1 requires AArch64)
-    else ifeq ($(CTX_INCLUDE_PAUTH_REGS),0)
-        $(error ENABLE_PAUTH=1 requires CTX_INCLUDE_PAUTH_REGS=1)
-    else
-        $(info ENABLE_PAUTH and CTX_INCLUDE_PAUTH_REGS are experimental features)
+    ifeq ($(CTX_INCLUDE_PAUTH_REGS),0)
+        $(error Pointer Authentication requires CTX_INCLUDE_PAUTH_REGS=1)
     endif
-else
-    ifeq ($(CTX_INCLUDE_PAUTH_REGS),1)
-        ifneq ($(ARCH),aarch64)
-            $(error CTX_INCLUDE_PAUTH_REGS=1 requires AArch64)
-        else
-            $(info CTX_INCLUDE_PAUTH_REGS is an experimental feature)
-        endif
+endif
+
+ifeq ($(CTX_INCLUDE_PAUTH_REGS),1)
+    ifneq (${ARCH},aarch64)
+        $(error CTX_INCLUDE_PAUTH_REGS requires AArch64)
+    else
+        $(info CTX_INCLUDE_PAUTH_REGS is an experimental feature)
     endif
 endif
 
+ifeq ($(ENABLE_PAUTH),1)
+    $(info Pointer Authentication is an experimental feature)
+endif
+
+ifeq ($(ENABLE_BTI),1)
+    $(info Branch Protection is an experimental feature)
+endif
+
 ################################################################################
 # Process platform overrideable behaviour
 ################################################################################
@@ -599,7 +630,6 @@ $(eval $(call assert_boolean,EL3_EXCEPTION_HANDLING))
 $(eval $(call assert_boolean,ENABLE_AMU))
 $(eval $(call assert_boolean,ENABLE_ASSERTIONS))
 $(eval $(call assert_boolean,ENABLE_MPAM_FOR_LOWER_ELS))
-$(eval $(call assert_boolean,ENABLE_PAUTH))
 $(eval $(call assert_boolean,ENABLE_PIE))
 $(eval $(call assert_boolean,ENABLE_PMF))
 $(eval $(call assert_boolean,ENABLE_PSCI_STAT))
@@ -635,6 +665,7 @@ $(eval $(call assert_boolean,BL2_IN_XIP_MEM))
 
 $(eval $(call assert_numeric,ARM_ARCH_MAJOR))
 $(eval $(call assert_numeric,ARM_ARCH_MINOR))
+$(eval $(call assert_numeric,BRANCH_PROTECTION))
 
 ################################################################################
 # Add definitions to the cpp preprocessor based on the current build options.
@@ -651,6 +682,7 @@ $(eval $(call add_define,CTX_INCLUDE_PAUTH_REGS))
 $(eval $(call add_define,EL3_EXCEPTION_HANDLING))
 $(eval $(call add_define,ENABLE_AMU))
 $(eval $(call add_define,ENABLE_ASSERTIONS))
+$(eval $(call add_define,ENABLE_BTI))
 $(eval $(call add_define,ENABLE_MPAM_FOR_LOWER_ELS))
 $(eval $(call add_define,ENABLE_PAUTH))
 $(eval $(call add_define,ENABLE_PIE))
diff --git a/bl1/bl1.mk b/bl1/bl1.mk
index 7f1a8230..b8399907 100644
--- a/bl1/bl1.mk
+++ b/bl1/bl1.mk
@@ -21,10 +21,6 @@ BL1_SOURCES		+=	lib/cpus/aarch64/dsu_helpers.S		\
 				lib/el3_runtime/aarch64/context.S
 endif
 
-ifeq (${ENABLE_PAUTH},1)
-BL1_CFLAGS		+=	-msign-return-address=non-leaf
-endif
-
 ifeq (${TRUSTED_BOARD_BOOT},1)
 BL1_SOURCES		+=	bl1/bl1_fwu.c
 endif
diff --git a/bl2/aarch64/bl2_el3_entrypoint.S b/bl2/aarch64/bl2_el3_entrypoint.S
index d1e42471..261d2957 100644
--- a/bl2/aarch64/bl2_el3_entrypoint.S
+++ b/bl2/aarch64/bl2_el3_entrypoint.S
@@ -10,7 +10,6 @@
 #include <el3_common_macros.S>
 
 	.globl	bl2_entrypoint
-	.globl	bl2_vector_table
 	.globl	bl2_el3_run_image
 	.globl	bl2_run_next_image
 
@@ -51,6 +50,13 @@ func bl2_entrypoint
 #if ENABLE_PAUTH
 	mrs	x0, sctlr_el3
 	orr	x0, x0, #SCTLR_EnIA_BIT
+#if ENABLE_BTI
+	/* ---------------------------------------------
+	 * Enable PAC branch type compatibility
+	 * ---------------------------------------------
+	 */
+	bic	x0, x0, #SCTLR_BT_BIT
+#endif	/* ENABLE_BTI */
 	msr	sctlr_el3, x0
 	isb
 #endif /* ENABLE_PAUTH */
diff --git a/bl2/aarch64/bl2_entrypoint.S b/bl2/aarch64/bl2_entrypoint.S
index c820cd13..5e5b83b1 100644
--- a/bl2/aarch64/bl2_entrypoint.S
+++ b/bl2/aarch64/bl2_entrypoint.S
@@ -124,6 +124,13 @@ func bl2_entrypoint
 #if ENABLE_PAUTH
 	mrs	x0, sctlr_el1
 	orr	x0, x0, #SCTLR_EnIA_BIT
+#if ENABLE_BTI
+	/* ---------------------------------------------
+	 * Enable PAC branch type compatibility
+	 * ---------------------------------------------
+	 */
+	bic	x0, x0, #(SCTLR_BT0_BIT | SCTLR_BT1_BIT)
+#endif	/* ENABLE_BTI */
 	msr	sctlr_el1, x0
 	isb
 #endif /* ENABLE_PAUTH */
diff --git a/bl2/bl2.mk b/bl2/bl2.mk
index 9523918b..6dc0f182 100644
--- a/bl2/bl2.mk
+++ b/bl2/bl2.mk
@@ -15,10 +15,6 @@ ifeq (${ARCH},aarch64)
 BL2_SOURCES		+=	common/aarch64/early_exceptions.S
 endif
 
-ifeq (${ENABLE_PAUTH},1)
-BL2_CFLAGS		+=	-msign-return-address=non-leaf
-endif
-
 ifeq (${BL2_AT_EL3},0)
 BL2_SOURCES		+=	bl2/${ARCH}/bl2_entrypoint.S
 BL2_LINKERFILE		:=	bl2/bl2.ld.S
diff --git a/bl31/aarch64/bl31_entrypoint.S b/bl31/aarch64/bl31_entrypoint.S
index f24458c1..e7ad5a89 100644
--- a/bl31/aarch64/bl31_entrypoint.S
+++ b/bl31/aarch64/bl31_entrypoint.S
@@ -105,6 +105,13 @@ func bl31_entrypoint
 #if ENABLE_PAUTH
 	mrs	x0, sctlr_el3
 	orr	x0, x0, #SCTLR_EnIA_BIT
+#if ENABLE_BTI
+	/* --------------------------------------------------------------------
+	 * Enable PAC branch type compatibility
+	 * --------------------------------------------------------------------
+	 */
+	bic	x0, x0, #SCTLR_BT_BIT
+#endif	/* ENABLE_BTI */
 	msr	sctlr_el3, x0
 	isb
 #endif /* ENABLE_PAUTH */
@@ -211,6 +218,13 @@ func bl31_warm_entrypoint
 
 	mrs	x0, sctlr_el3
 	orr	x0, x0, #SCTLR_EnIA_BIT
+#if ENABLE_BTI
+	/* --------------------------------------------------------------------
+	 * Enable PAC branch type compatibility
+	 * --------------------------------------------------------------------
+	 */
+	bic	x0, x0, #SCTLR_BT_BIT
+#endif	/* ENABLE_BTI */
 	msr	sctlr_el3, x0
 	isb
 #endif /* ENABLE_PAUTH */
diff --git a/bl31/bl31.mk b/bl31/bl31.mk
index 10feae16..c9ba926c 100644
--- a/bl31/bl31.mk
+++ b/bl31/bl31.mk
@@ -75,10 +75,6 @@ ifeq (${ENABLE_MPAM_FOR_LOWER_ELS},1)
 BL31_SOURCES		+=	lib/extensions/mpam/mpam.c
 endif
 
-ifeq (${ENABLE_PAUTH},1)
-BL31_CFLAGS		+=	-msign-return-address=non-leaf
-endif
-
 ifeq (${WORKAROUND_CVE_2017_5715},1)
 BL31_SOURCES		+=	lib/cpus/aarch64/wa_cve_2017_5715_bpiall.S	\
 				lib/cpus/aarch64/wa_cve_2017_5715_mmu.S
diff --git a/bl32/tsp/aarch64/tsp_entrypoint.S b/bl32/tsp/aarch64/tsp_entrypoint.S
index cd08ce7d..fd6b0fbc 100644
--- a/bl32/tsp/aarch64/tsp_entrypoint.S
+++ b/bl32/tsp/aarch64/tsp_entrypoint.S
@@ -136,6 +136,13 @@ func tsp_entrypoint _align=3
 #if ENABLE_PAUTH
 	mrs	x0, sctlr_el1
 	orr	x0, x0, #SCTLR_EnIA_BIT
+#if ENABLE_BTI
+	/* ---------------------------------------------
+	 * Enable PAC branch type compatibility
+	 * ---------------------------------------------
+	 */
+	bic	x0, x0, #(SCTLR_BT0_BIT | SCTLR_BT1_BIT)
+#endif	/* ENABLE_BTI */
 	msr	sctlr_el1, x0
 	isb
 #endif /* ENABLE_PAUTH */
@@ -164,7 +171,7 @@ endfunc tsp_entrypoint
 	 * TSPD for the various entrypoints
 	 * -------------------------------------------
 	 */
-func tsp_vector_table
+vector_base tsp_vector_table
 	b	tsp_yield_smc_entry
 	b	tsp_fast_smc_entry
 	b	tsp_cpu_on_entry
@@ -175,7 +182,6 @@ func tsp_vector_table
 	b	tsp_system_off_entry
 	b	tsp_system_reset_entry
 	b	tsp_abort_yield_smc_entry
-endfunc tsp_vector_table
 
 	/*---------------------------------------------
 	 * This entrypoint is used by the TSPD when this
diff --git a/bl32/tsp/tsp.mk b/bl32/tsp/tsp.mk
index b1fe7ff6..3fd6d995 100644
--- a/bl32/tsp/tsp.mk
+++ b/bl32/tsp/tsp.mk
@@ -17,11 +17,6 @@ BL32_SOURCES		+=	bl32/tsp/tsp_main.c			\
 
 BL32_LINKERFILE		:=	bl32/tsp/tsp.ld.S
 
-# This flag determines whether pointer authentication is used in the TSP or not
-ifeq ($(ENABLE_PAUTH),1)
-BL32_CFLAGS		+=	-msign-return-address=non-leaf
-endif
-
 # This flag determines if the TSPD initializes BL32 in tspd_init() (synchronous
 # method) or configures BL31 to pass control to BL32 instead of BL33
 # (asynchronous method).
diff --git a/docs/design/firmware-design.rst b/docs/design/firmware-design.rst
index 21b82346..e4e2bc1d 100644
--- a/docs/design/firmware-design.rst
+++ b/docs/design/firmware-design.rst
@@ -2564,7 +2564,7 @@ Armv8.3-A
    to the context that is saved when doing a world switch.
 
    The TF-A itself has support for pointer authentication at runtime
-   that can be enabled by setting both options ``ENABLE_PAUTH`` and
+   that can be enabled by setting ``BRANCH_PROTECTION`` option to non-zero and
    ``CTX_INCLUDE_PAUTH_REGS`` to 1. This enables pointer authentication in BL1,
    BL2, BL31, and the TSP if it is used.
 
@@ -2577,6 +2577,12 @@ Armv8.3-A
    enabling PAuth is lower because the compiler will use the optimized
    PAuth instructions rather than the backwards-compatible ones.
 
+Armv8.5-A
+~~~~~~~~~
+
+-  Branch Target Identification feature is selected by ``BRANCH_PROTECTION``
+   option set to 1. This option defaults to 0 and this is an experimental feature.
+
 Armv7-A
 ~~~~~~~
 
diff --git a/docs/getting_started/user-guide.rst b/docs/getting_started/user-guide.rst
index 60654644..db365488 100644
--- a/docs/getting_started/user-guide.rst
+++ b/docs/getting_started/user-guide.rst
@@ -315,6 +315,34 @@ Common build options
    file that contains the BL33 private key in PEM format. If ``SAVE_KEYS=1``,
    this file name will be used to save the key.
 
+-  ``BRANCH_PROTECTION``: Numeric value to enable ARMv8.3 Pointer Authentication
+   and ARMv8.5 Branch Target Identification support for TF-A BL images themselves.
+   If enabled, it is needed to use a compiler that supports the option
+   ``-mbranch-protection``. Selects the branch protection features to use:
+-  0: Default value turns off all types of branch protection
+-  1: Enables all types of branch protection features
+-  2: Return address signing to its standard level
+-  3: Extend the signing to include leaf functions
+
+   The table below summarizes ``BRANCH_PROTECTION`` values, GCC compilation options
+   and resulting PAuth/BTI features.
+
+   +-------+--------------+-------+-----+
+   | Value |  GCC option  | PAuth | BTI |
+   +=======+==============+=======+=====+
+   |   0   |     none     |   N   |  N  |
+   +-------+--------------+-------+-----+
+   |   1   |   standard   |   Y   |  Y  |
+   +-------+--------------+-------+-----+
+   |   2   |   pac-ret    |   Y   |  N  |
+   +-------+--------------+-------+-----+
+   |   3   | pac-ret+leaf |   Y   |  N  |
+   +-------+--------------+-------+-----+
+
+   This option defaults to 0 and this is an experimental feature.
+   Note that Pointer Authentication is enabled for Non-secure world
+   irrespective of the value of this option if the CPU supports it.
+
 -  ``BUILD_MESSAGE_TIMESTAMP``: String used to identify the time and date of the
    compilation of each build. It must be set to a C string (including quotes
    where applicable). Defaults to a string that contains the time and date of
@@ -354,17 +382,12 @@ Common build options
    registers to be included when saving and restoring the CPU context. Default
    is 0.
 
--  ``CTX_INCLUDE_PAUTH_REGS``: Boolean option that, when set to 1, allows
-   Pointer Authentication for **Secure world**. This will cause the
-   Armv8.3-PAuth registers to be included when saving and restoring the CPU
-   context as part of a world switch. Default value is 0. Pointer Authentication
-   is an experimental feature.
-
-   Note that, if the CPU supports it, Pointer Authentication is allowed for
-   Non-secure world irrespectively of the value of this flag. "Allowed" means
-   that accesses to PAuth-related registers or execution of PAuth-related
-   instructions will not be trapped to EL3. As such, usage or not of PAuth in
-   Non-secure world images, depends on those images themselves.
+-  ``CTX_INCLUDE_PAUTH_REGS``: Boolean option that, when set to 1, enables
+   Pointer Authentication for Secure world. This will cause the ARMv8.3-PAuth
+   registers to be included when saving and restoring the CPU context as
+   part of world switch. Default value is 0 and this is an experimental feature.
+   Note that Pointer Authentication is enabled for Non-secure world irrespective
+   of the value of this flag if the CPU supports it.
 
 -  ``DEBUG``: Chooses between a debug and release build. It can take either 0
    (release) or 1 (debug) as values. 0 is the default.
@@ -417,13 +440,6 @@ Common build options
    partitioning in EL3, however. Platform initialisation code should configure
    and use partitions in EL3 as required. This option defaults to ``0``.
 
--  ``ENABLE_PAUTH``: Boolean option to enable Armv8.3 Pointer Authentication
-   for **TF-A BL images themselves**. If enabled, the compiler must support the
-   ``-msign-return-address`` option. This flag defaults to 0. Pointer
-   Authentication is an experimental feature.
-
-   If this flag is enabled, ``CTX_INCLUDE_PAUTH_REGS`` must also be enabled.
-
 -  ``ENABLE_PIE``: Boolean option to enable Position Independent Executable(PIE)
    support within generic code in TF-A. This option is currently only supported
    in BL31. Default is 0.
diff --git a/include/arch/aarch64/arch.h b/include/arch/aarch64/arch.h
index d15851d8..d23d89e3 100644
--- a/include/arch/aarch64/arch.h
+++ b/include/arch/aarch64/arch.h
@@ -163,16 +163,12 @@
 /* ID_AA64ISAR1_EL1 definitions */
 #define ID_AA64ISAR1_EL1	S3_0_C0_C6_1
 #define ID_AA64ISAR1_GPI_SHIFT	U(28)
-#define ID_AA64ISAR1_GPI_WIDTH	U(4)
 #define ID_AA64ISAR1_GPI_MASK	ULL(0xf)
 #define ID_AA64ISAR1_GPA_SHIFT	U(24)
-#define ID_AA64ISAR1_GPA_WIDTH	U(4)
 #define ID_AA64ISAR1_GPA_MASK	ULL(0xf)
 #define ID_AA64ISAR1_API_SHIFT	U(8)
-#define ID_AA64ISAR1_API_WIDTH	U(4)
 #define ID_AA64ISAR1_API_MASK	ULL(0xf)
 #define ID_AA64ISAR1_APA_SHIFT	U(4)
-#define ID_AA64ISAR1_APA_WIDTH	U(4)
 #define ID_AA64ISAR1_APA_MASK	ULL(0xf)
 
 /* ID_AA64MMFR0_EL1 definitions */
@@ -217,6 +213,11 @@
 
 #define SSBS_UNAVAILABLE	ULL(0)	/* No architectural SSBS support */
 
+#define ID_AA64PFR1_EL1_BT_SHIFT	U(0)
+#define ID_AA64PFR1_EL1_BT_MASK		ULL(0xf)
+
+#define BTI_IMPLEMENTED		ULL(1)	/* The BTI mechanism is implemented */
+
 /* ID_PFR1_EL1 definitions */
 #define ID_PFR1_VIRTEXT_SHIFT	U(12)
 #define ID_PFR1_VIRTEXT_MASK	U(0xf)
@@ -260,6 +261,9 @@
 #define SCTLR_EE_BIT		(ULL(1) << 25)
 #define SCTLR_UCI_BIT		(ULL(1) << 26)
 #define SCTLR_EnIA_BIT		(ULL(1) << 31)
+#define SCTLR_BT0_BIT		(ULL(1) << 35)
+#define SCTLR_BT1_BIT		(ULL(1) << 36)
+#define SCTLR_BT_BIT		(ULL(1) << 36)
 #define SCTLR_DSSBS_BIT		(ULL(1) << 44)
 #define SCTLR_RESET_VAL		SCTLR_EL3_RES1
 
diff --git a/include/arch/aarch64/arch_features.h b/include/arch/aarch64/arch_features.h
index 6af1d039..1129b8e4 100644
--- a/include/arch/aarch64/arch_features.h
+++ b/include/arch/aarch64/arch_features.h
@@ -48,4 +48,10 @@ static inline bool is_armv8_4_ttst_present(void)
 		ID_AA64MMFR2_EL1_ST_MASK) == 1U;
 }
 
+static inline bool is_armv8_5_bti_present(void)
+{
+	return ((read_id_aa64pfr1_el1() >> ID_AA64PFR1_EL1_BT_SHIFT) &
+		ID_AA64PFR1_EL1_BT_MASK) == BTI_IMPLEMENTED;
+}
+
 #endif /* ARCH_FEATURES_H */
diff --git a/include/arch/aarch64/asm_macros.S b/include/arch/aarch64/asm_macros.S
index 9b121855..79e0ad7f 100644
--- a/include/arch/aarch64/asm_macros.S
+++ b/include/arch/aarch64/asm_macros.S
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2013-2018, ARM Limited and Contributors. All rights reserved.
+ * Copyright (c) 2013-2019, ARM Limited and Contributors. All rights reserved.
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */
@@ -10,6 +10,10 @@
 #include <common/asm_macros_common.S>
 #include <lib/spinlock.h>
 
+#if ENABLE_BTI && !ARM_ARCH_AT_LEAST(8, 5)
+#error Branch Target Identification requires ARM_ARCH_MINOR >= 5
+#endif
+
 /*
  * TLBI instruction with type specifier that implements the workaround for
  * errata 813419 of Cortex-A57 or errata 1286807 of Cortex-A76.
@@ -192,4 +196,26 @@
 	.endm
 #endif
 
+	/*
+	 * Helper macro to read system register value into x0
+	 */
+	.macro	read reg:req
+#if ENABLE_BTI
+	bti	j
+#endif
+	mrs	x0, \reg
+	ret
+	.endm
+
+	/*
+	 * Helper macro to write value from x1 to system register
+	 */
+	.macro	write reg:req
+#if ENABLE_BTI
+	bti	j
+#endif
+	msr	\reg, x1
+	ret
+	.endm
+
 #endif /* ASM_MACROS_S */
diff --git a/include/common/asm_macros_common.S b/include/common/asm_macros_common.S
index 09742af1..fd0ea81d 100644
--- a/include/common/asm_macros_common.S
+++ b/include/common/asm_macros_common.S
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2013-2018, ARM Limited and Contributors. All rights reserved.
+ * Copyright (c) 2013-2019, ARM Limited and Contributors. All rights reserved.
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */
@@ -38,6 +38,12 @@
 	.cfi_startproc
 	.align \_align
 	\_name:
+#if ENABLE_BTI
+	/* When Branch Target Identification is enabled, insert "bti jc"
+	 * instruction to enable indirect calls and branches
+	 */
+	 bti	jc
+#endif
 	.endm
 
 	/*
diff --git a/include/lib/xlat_tables/xlat_tables_defs.h b/include/lib/xlat_tables/xlat_tables_defs.h
index f9bbe0f6..000811f3 100644
--- a/include/lib/xlat_tables/xlat_tables_defs.h
+++ b/include/lib/xlat_tables/xlat_tables_defs.h
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2017-2018, ARM Limited and Contributors. All rights reserved.
+ * Copyright (c) 2017-2019, ARM Limited and Contributors. All rights reserved.
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */
@@ -62,6 +62,11 @@
 #define OSH			(U(0x2) << 6)
 #define ISH			(U(0x3) << 6)
 
+#ifdef AARCH64
+/* Guarded Page bit */
+#define GP			(ULL(1) << 50)
+#endif
+
 #define TABLE_ADDR_MASK		ULL(0x0000FFFFFFFFF000)
 
 /*
diff --git a/lib/aarch64/cache_helpers.S b/lib/aarch64/cache_helpers.S
index 9c40b9db..9ef8ca79 100644
--- a/lib/aarch64/cache_helpers.S
+++ b/lib/aarch64/cache_helpers.S
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2013-2014, ARM Limited and Contributors. All rights reserved.
+ * Copyright (c) 2013-2019, ARM Limited and Contributors. All rights reserved.
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */
@@ -91,6 +91,9 @@ func do_dcsw_op
 	cbz	x3, exit
 	adr	x14, dcsw_loop_table	// compute inner loop address
 	add	x14, x14, x0, lsl #5	// inner loop is 8x32-bit instructions
+#if ENABLE_BTI
+	add	x14, x14, x0, lsl #2	// inner loop is + "bti j" instruction
+#endif
 	mov	x0, x9
 	mov	w8, #1
 loop1:
@@ -116,6 +119,9 @@ loop1:
 	br	x14			// jump to DC operation specific loop
 
 	.macro	dcsw_loop _op
+#if ENABLE_BTI
+	bti	j
+#endif
 loop2_\_op:
 	lsl	w7, w6, w2		// w7 = aligned max set number
 
diff --git a/lib/cpus/aarch64/cpuamu_helpers.S b/lib/cpus/aarch64/cpuamu_helpers.S
index 79b72883..5a77fc7b 100644
--- a/lib/cpus/aarch64/cpuamu_helpers.S
+++ b/lib/cpus/aarch64/cpuamu_helpers.S
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2018, ARM Limited and Contributors. All rights reserved.
+ * Copyright (c) 2018-2019, ARM Limited and Contributors. All rights reserved.
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */
@@ -23,21 +23,17 @@
  */
 func cpuamu_cnt_read
 	adr	x1, 1f
-	lsl	x0, x0, #3
-	add	x1, x1, x0
+	add	x1, x1, x0, lsl #3	/* each mrs/ret sequence is 8 bytes */
+#if ENABLE_BTI
+	add	x1, x1, x0, lsl #2	/* + "bti j" instruction */
+#endif
 	br	x1
 
-1:
-	mrs	x0, CPUAMEVCNTR0_EL0
-	ret
-	mrs	x0, CPUAMEVCNTR1_EL0
-	ret
-	mrs	x0, CPUAMEVCNTR2_EL0
-	ret
-	mrs	x0, CPUAMEVCNTR3_EL0
-	ret
-	mrs	x0, CPUAMEVCNTR4_EL0
-	ret
+1:	read	CPUAMEVCNTR0_EL0
+	read	CPUAMEVCNTR1_EL0
+	read	CPUAMEVCNTR2_EL0
+	read	CPUAMEVCNTR3_EL0
+	read	CPUAMEVCNTR4_EL0
 endfunc cpuamu_cnt_read
 
 /*
@@ -47,21 +43,17 @@ endfunc cpuamu_cnt_read
  */
 func cpuamu_cnt_write
 	adr	x2, 1f
-	lsl	x0, x0, #3
-	add	x2, x2, x0
+	add	x2, x2, x0, lsl #3	/* each msr/ret sequence is 8 bytes */
+#if ENABLE_BTI
+	add	x2, x2, x0, lsl #2	/* + "bti j" instruction */
+#endif
 	br	x2
 
-1:
-	msr	CPUAMEVCNTR0_EL0, x0
-	ret
-	msr	CPUAMEVCNTR1_EL0, x0
-	ret
-	msr	CPUAMEVCNTR2_EL0, x0
-	ret
-	msr	CPUAMEVCNTR3_EL0, x0
-	ret
-	msr	CPUAMEVCNTR4_EL0, x0
-	ret
+1:	write	CPUAMEVCNTR0_EL0
+	write	CPUAMEVCNTR1_EL0
+	write	CPUAMEVCNTR2_EL0
+	write	CPUAMEVCNTR3_EL0
+	write	CPUAMEVCNTR4_EL0
 endfunc cpuamu_cnt_write
 
 /*
diff --git a/lib/extensions/amu/aarch64/amu_helpers.S b/lib/extensions/amu/aarch64/amu_helpers.S
index e0b1f564..89007a3f 100644
--- a/lib/extensions/amu/aarch64/amu_helpers.S
+++ b/lib/extensions/amu/aarch64/amu_helpers.S
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2017, ARM Limited and Contributors. All rights reserved.
+ * Copyright (c) 2017-2019, ARM Limited and Contributors. All rights reserved.
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */
@@ -21,35 +21,29 @@
  * and return it in `x0`.
  */
 func amu_group0_cnt_read_internal
+	adr	x1, 1f
 #if ENABLE_ASSERTIONS
 	/*
 	 * It can be dangerous to call this function with an
 	 * out of bounds index.  Ensure `idx` is valid.
 	 */
-	mov	x1, x0
-	lsr	x1, x1, #2
-	cmp	x1, #0
+	tst	x0, #~3
 	ASM_ASSERT(eq)
 #endif
-
 	/*
 	 * Given `idx` calculate address of mrs/ret instruction pair
 	 * in the table below.
 	 */
-	adr	x1, 1f
-	lsl	x0, x0, #3		/* each mrs/ret sequence is 8 bytes */
-	add	x1, x1, x0
+	add	x1, x1, x0, lsl #3	/* each mrs/ret sequence is 8 bytes */
+#if ENABLE_BTI
+	add	x1, x1, x0, lsl #2	/* + "bti j" instruction */
+#endif
 	br	x1
 
-1:
-	mrs	x0, AMEVCNTR00_EL0	/* index 0 */
-	ret
-	mrs	x0, AMEVCNTR01_EL0	/* index 1 */
-	ret
-	mrs	x0, AMEVCNTR02_EL0	/* index 2 */
-	ret
-	mrs	x0, AMEVCNTR03_EL0	/* index 3 */
-	ret
+1:	read	AMEVCNTR00_EL0		/* index 0 */
+	read	AMEVCNTR01_EL0		/* index 1 */
+	read	AMEVCNTR02_EL0		/* index 2 */
+	read	AMEVCNTR03_EL0		/* index 3 */
 endfunc amu_group0_cnt_read_internal
 
 /*
@@ -58,35 +52,29 @@ endfunc amu_group0_cnt_read_internal
  * Given `idx`, write `val` to the corresponding AMU counter.
  */
 func amu_group0_cnt_write_internal
+	adr	x2, 1f
 #if ENABLE_ASSERTIONS
 	/*
 	 * It can be dangerous to call this function with an
 	 * out of bounds index.  Ensure `idx` is valid.
 	 */
-	mov	x2, x0
-	lsr	x2, x2, #2
-	cmp	x2, #0
+	tst	x0, #~3
 	ASM_ASSERT(eq)
 #endif
-
 	/*
 	 * Given `idx` calculate address of mrs/ret instruction pair
 	 * in the table below.
 	 */
-	adr	x2, 1f
-	lsl	x0, x0, #3		/* each msr/ret sequence is 8 bytes */
-	add	x2, x2, x0
+	add	x2, x2, x0, lsl #3	/* each msr/ret sequence is 8 bytes */
+#if ENABLE_BTI
+	add	x2, x2, x0, lsl #2	/* + "bti j" instruction */
+#endif
 	br	x2
 
-1:
-	msr	AMEVCNTR00_EL0, x1	/* index 0 */
-	ret
-	msr	AMEVCNTR01_EL0, x1	/* index 1 */
-	ret
-	msr	AMEVCNTR02_EL0, x1	/* index 2 */
-	ret
-	msr	AMEVCNTR03_EL0, x1	/* index 3 */
-	ret
+1:	write	AMEVCNTR00_EL0		/* index 0 */
+	write	AMEVCNTR01_EL0		/* index 1 */
+	write	AMEVCNTR02_EL0		/* index 2 */
+	write	AMEVCNTR03_EL0		/* index 3 */
 endfunc amu_group0_cnt_write_internal
 
 /*
@@ -96,59 +84,41 @@ endfunc amu_group0_cnt_write_internal
  * and return it in `x0`.
  */
 func amu_group1_cnt_read_internal
+	adr	x1, 1f
 #if ENABLE_ASSERTIONS
 	/*
 	 * It can be dangerous to call this function with an
 	 * out of bounds index.  Ensure `idx` is valid.
 	 */
-	mov	x1, x0
-	lsr	x1, x1, #4
-	cmp	x1, #0
+	tst	x0, #~0xF
 	ASM_ASSERT(eq)
 #endif
-
 	/*
 	 * Given `idx` calculate address of mrs/ret instruction pair
 	 * in the table below.
 	 */
-	adr	x1, 1f
-	lsl	x0, x0, #3		/* each mrs/ret sequence is 8 bytes */
-	add	x1, x1, x0
+	add	x1, x1, x0, lsl #3	/* each mrs/ret sequence is 8 bytes */
+#if ENABLE_BTI
+	add	x1, x1, x0, lsl #2	/* + "bti j" instruction */
+#endif
 	br	x1
 
-1:
-	mrs	x0, AMEVCNTR10_EL0	/* index 0 */
-	ret
-	mrs	x0, AMEVCNTR11_EL0	/* index 1 */
-	ret
-	mrs	x0, AMEVCNTR12_EL0	/* index 2 */
-	ret
-	mrs	x0, AMEVCNTR13_EL0	/* index 3 */
-	ret
-	mrs	x0, AMEVCNTR14_EL0	/* index 4 */
-	ret
-	mrs	x0, AMEVCNTR15_EL0	/* index 5 */
-	ret
-	mrs	x0, AMEVCNTR16_EL0	/* index 6 */
-	ret
-	mrs	x0, AMEVCNTR17_EL0	/* index 7 */
-	ret
-	mrs	x0, AMEVCNTR18_EL0	/* index 8 */
-	ret
-	mrs	x0, AMEVCNTR19_EL0	/* index 9 */
-	ret
-	mrs	x0, AMEVCNTR1A_EL0	/* index 10 */
-	ret
-	mrs	x0, AMEVCNTR1B_EL0	/* index 11 */
-	ret
-	mrs	x0, AMEVCNTR1C_EL0	/* index 12 */
-	ret
-	mrs	x0, AMEVCNTR1D_EL0	/* index 13 */
-	ret
-	mrs	x0, AMEVCNTR1E_EL0	/* index 14 */
-	ret
-	mrs	x0, AMEVCNTR1F_EL0	/* index 15 */
-	ret
+1:	read	AMEVCNTR10_EL0		/* index 0 */
+	read	AMEVCNTR11_EL0		/* index 1 */
+	read	AMEVCNTR12_EL0		/* index 2 */
+	read	AMEVCNTR13_EL0		/* index 3 */
+	read	AMEVCNTR14_EL0		/* index 4 */
+	read	AMEVCNTR15_EL0		/* index 5 */
+	read	AMEVCNTR16_EL0		/* index 6 */
+	read	AMEVCNTR17_EL0		/* index 7 */
+	read	AMEVCNTR18_EL0		/* index 8 */
+	read	AMEVCNTR19_EL0		/* index 9 */
+	read	AMEVCNTR1A_EL0		/* index 10 */
+	read	AMEVCNTR1B_EL0		/* index 11 */
+	read	AMEVCNTR1C_EL0		/* index 12 */
+	read	AMEVCNTR1D_EL0		/* index 13 */
+	read	AMEVCNTR1E_EL0		/* index 14 */
+	read	AMEVCNTR1F_EL0		/* index 15 */
 endfunc amu_group1_cnt_read_internal
 
 /*
@@ -157,59 +127,41 @@ endfunc amu_group1_cnt_read_internal
  * Given `idx`, write `val` to the corresponding AMU counter.
  */
 func amu_group1_cnt_write_internal
+	adr	x2, 1f
 #if ENABLE_ASSERTIONS
 	/*
 	 * It can be dangerous to call this function with an
 	 * out of bounds index.  Ensure `idx` is valid.
 	 */
-	mov	x2, x0
-	lsr	x2, x2, #4
-	cmp	x2, #0
+	tst	x0, #~0xF
 	ASM_ASSERT(eq)
 #endif
-
 	/*
 	 * Given `idx` calculate address of mrs/ret instruction pair
 	 * in the table below.
 	 */
-	adr	x2, 1f
-	lsl	x0, x0, #3		/* each msr/ret sequence is 8 bytes */
-	add	x2, x2, x0
+	add	x2, x2, x0, lsl #3	/* each msr/ret sequence is 8 bytes */
+#if ENABLE_BTI
+	add	x2, x2, x0, lsl #2	/* + "bti j" instruction */
+#endif
 	br	x2
 
-1:
-	msr	AMEVCNTR10_EL0, x1	/* index 0 */
-	ret
-	msr	AMEVCNTR11_EL0, x1	/* index 1 */
-	ret
-	msr	AMEVCNTR12_EL0, x1	/* index 2 */
-	ret
-	msr	AMEVCNTR13_EL0, x1	/* index 3 */
-	ret
-	msr	AMEVCNTR14_EL0, x1	/* index 4 */
-	ret
-	msr	AMEVCNTR15_EL0, x1	/* index 5 */
-	ret
-	msr	AMEVCNTR16_EL0, x1	/* index 6 */
-	ret
-	msr	AMEVCNTR17_EL0, x1	/* index 7 */
-	ret
-	msr	AMEVCNTR18_EL0, x1	/* index 8 */
-	ret
-	msr	AMEVCNTR19_EL0, x1	/* index 9 */
-	ret
-	msr	AMEVCNTR1A_EL0, x1	/* index 10 */
-	ret
-	msr	AMEVCNTR1B_EL0, x1	/* index 11 */
-	ret
-	msr	AMEVCNTR1C_EL0, x1	/* index 12 */
-	ret
-	msr	AMEVCNTR1D_EL0, x1	/* index 13 */
-	ret
-	msr	AMEVCNTR1E_EL0, x1	/* index 14 */
-	ret
-	msr	AMEVCNTR1F_EL0, x1	/* index 15 */
-	ret
+1:	write	AMEVCNTR10_EL0		/* index 0 */
+	write	AMEVCNTR11_EL0		/* index 1 */
+	write	AMEVCNTR12_EL0		/* index 2 */
+	write	AMEVCNTR13_EL0		/* index 3 */
+	write	AMEVCNTR14_EL0		/* index 4 */
+	write	AMEVCNTR15_EL0		/* index 5 */
+	write	AMEVCNTR16_EL0		/* index 6 */
+	write	AMEVCNTR17_EL0		/* index 7 */
+	write	AMEVCNTR18_EL0		/* index 8 */
+	write	AMEVCNTR19_EL0		/* index 9 */
+	write	AMEVCNTR1A_EL0		/* index 10 */
+	write	AMEVCNTR1B_EL0		/* index 11 */
+	write	AMEVCNTR1C_EL0		/* index 12 */
+	write	AMEVCNTR1D_EL0		/* index 13 */
+	write	AMEVCNTR1E_EL0		/* index 14 */
+	write	AMEVCNTR1F_EL0		/* index 15 */
 endfunc amu_group1_cnt_write_internal
 
 /*
@@ -219,63 +171,43 @@ endfunc amu_group1_cnt_write_internal
  * with the value `val`.
  */
 func amu_group1_set_evtype_internal
+	adr	x2, 1f
 #if ENABLE_ASSERTIONS
 	/*
 	 * It can be dangerous to call this function with an
 	 * out of bounds index.  Ensure `idx` is valid.
 	 */
-	mov	x2, x0
-	lsr	x2, x2, #4
-	cmp	x2, #0
+	tst	x0, #~0xF
 	ASM_ASSERT(eq)
 
 	/* val should be between [0, 65535] */
-	mov	x2, x1
-	lsr	x2, x2, #16
-	cmp	x2, #0
+	tst	x1, #~0xFFFF
 	ASM_ASSERT(eq)
 #endif
-
 	/*
 	 * Given `idx` calculate address of msr/ret instruction pair
 	 * in the table below.
 	 */
-	adr	x2, 1f
-	lsl	x0, x0, #3		/* each msr/ret sequence is 8 bytes */
-	add	x2, x2, x0
+	add	x2, x2, x0, lsl #3	/* each msr/ret sequence is 8 bytes */
+#if ENABLE_BTI
+	add	x2, x2, x0, lsl #2	/* + "bti j" instruction */
+#endif
 	br	x2
 
-1:
-	msr	AMEVTYPER10_EL0, x1	/* index 0 */
-	ret
-	msr	AMEVTYPER11_EL0, x1	/* index 1 */
-	ret
-	msr	AMEVTYPER12_EL0, x1	/* index 2 */
-	ret
-	msr	AMEVTYPER13_EL0, x1	/* index 3 */
-	ret
-	msr	AMEVTYPER14_EL0, x1	/* index 4 */
-	ret
-	msr	AMEVTYPER15_EL0, x1	/* index 5 */
-	ret
-	msr	AMEVTYPER16_EL0, x1	/* index 6 */
-	ret
-	msr	AMEVTYPER17_EL0, x1	/* index 7 */
-	ret
-	msr	AMEVTYPER18_EL0, x1	/* index 8 */
-	ret
-	msr	AMEVTYPER19_EL0, x1	/* index 9 */
-	ret
-	msr	AMEVTYPER1A_EL0, x1	/* index 10 */
-	ret
-	msr	AMEVTYPER1B_EL0, x1	/* index 11 */
-	ret
-	msr	AMEVTYPER1C_EL0, x1	/* index 12 */
-	ret
-	msr	AMEVTYPER1D_EL0, x1	/* index 13 */
-	ret
-	msr	AMEVTYPER1E_EL0, x1	/* index 14 */
-	ret
-	msr	AMEVTYPER1F_EL0, x1	/* index 15 */
-	ret
+1:	write	AMEVTYPER10_EL0		/* index 0 */
+	write	AMEVTYPER11_EL0		/* index 1 */
+	write	AMEVTYPER12_EL0		/* index 2 */
+	write	AMEVTYPER13_EL0		/* index 3 */
+	write	AMEVTYPER14_EL0		/* index 4 */
+	write	AMEVTYPER15_EL0		/* index 5 */
+	write	AMEVTYPER16_EL0		/* index 6 */
+	write	AMEVTYPER17_EL0		/* index 7 */
+	write	AMEVTYPER18_EL0		/* index 8 */
+	write	AMEVTYPER19_EL0		/* index 9 */
+	write	AMEVTYPER1A_EL0		/* index 10 */
+	write	AMEVTYPER1B_EL0		/* index 11 */
+	write	AMEVTYPER1C_EL0		/* index 12 */
+	write	AMEVTYPER1D_EL0		/* index 13 */
+	write	AMEVTYPER1E_EL0		/* index 14 */
+	write	AMEVTYPER1F_EL0		/* index 15 */
 endfunc amu_group1_set_evtype_internal
diff --git a/lib/xlat_tables_v2/xlat_tables_core.c b/lib/xlat_tables_v2/xlat_tables_core.c
index 0e6a6fa8..4f62f469 100644
--- a/lib/xlat_tables_v2/xlat_tables_core.c
+++ b/lib/xlat_tables_v2/xlat_tables_core.c
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2017-2018, ARM Limited and Contributors. All rights reserved.
+ * Copyright (c) 2017-2019, ARM Limited and Contributors. All rights reserved.
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */
@@ -12,6 +12,7 @@
 
 #include <platform_def.h>
 
+#include <arch_features.h>
 #include <arch_helpers.h>
 #include <common/debug.h>
 #include <lib/utils_def.h>
@@ -195,6 +196,18 @@ uint64_t xlat_desc(const xlat_ctx_t *ctx, uint32_t attr,
 
 		if (mem_type == MT_MEMORY) {
 			desc |= LOWER_ATTRS(ATTR_IWBWA_OWBWA_NTR_INDEX | ISH);
+
+			/* Check if Branch Target Identification is enabled */
+#if ENABLE_BTI
+			/* Set GP bit for block and page code entries
+			 * if BTI mechanism is implemented.
+			 */
+			if (is_armv8_5_bti_present() &&
+			   ((attr & (MT_TYPE_MASK | MT_RW |
+				MT_EXECUTE_NEVER)) == MT_CODE)) {
+				desc |= GP;
+			}
+#endif
 		} else {
 			assert(mem_type == MT_NON_CACHEABLE);
 			desc |= LOWER_ATTRS(ATTR_NON_CACHEABLE_INDEX | OSH);
diff --git a/lib/xlat_tables_v2/xlat_tables_utils.c b/lib/xlat_tables_v2/xlat_tables_utils.c
index f5848a25..761d00c3 100644
--- a/lib/xlat_tables_v2/xlat_tables_utils.c
+++ b/lib/xlat_tables_v2/xlat_tables_utils.c
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2017-2018, ARM Limited and Contributors. All rights reserved.
+ * Copyright (c) 2017-2019, ARM Limited and Contributors. All rights reserved.
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */
@@ -96,6 +96,13 @@ static void xlat_desc_print(const xlat_ctx_t *ctx, uint64_t desc)
 	}
 
 	printf(((LOWER_ATTRS(NS) & desc) != 0ULL) ? "-NS" : "-S");
+
+#ifdef AARCH64
+	/* Check Guarded Page bit */
+	if ((desc & GP) != 0ULL) {
+		printf("-GP");
+	}
+#endif
 }
 
 static const char * const level_spacers[] = {
diff --git a/make_helpers/defaults.mk b/make_helpers/defaults.mk
index dc797ed1..6becf808 100644
--- a/make_helpers/defaults.mk
+++ b/make_helpers/defaults.mk
@@ -33,6 +33,9 @@ BL2_AT_EL3			:= 0
 # when BL2_AT_EL3 is 1.
 BL2_IN_XIP_MEM			:= 0
 
+# Select the branch protection features to use.
+BRANCH_PROTECTION		:= 0
+
 # By default, consider that the platform may release several CPUs out of reset.
 # The platform Makefile is free to override this value.
 COLD_BOOT_SINGLE_CPU		:= 0
@@ -90,7 +93,14 @@ ENABLE_STACK_PROTECTOR		:= 0
 # Flag to enable exception handling in EL3
 EL3_EXCEPTION_HANDLING		:= 0
 
-# Flag to enable Pointer Authentication
+# Flag to enable Branch Target Identification.
+# Internal flag not meant for direct setting.
+# Use BRANCH_PROTECTION to enable BTI.
+ENABLE_BTI			:= 0
+
+# Flag to enable Pointer Authentication.
+# Internal flag not meant for direct setting.
+# Use BRANCH_PROTECTION to enable PAUTH.
 ENABLE_PAUTH			:= 0
 
 # Build flag to treat usage of deprecated platform and framework APIs as error.