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>

3 files changed, 41 insertions, 5 deletions

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 */