Enable MTE support in both secure and non-secure worlds

This patch adds support for the new Memory Tagging Extension arriving in
ARMv8.5. MTE support is now enabled by default on systems that support
at EL0. To enable it at ELx for both the non-secure and the secure
world, the compiler flag CTX_INCLUDE_MTE_REGS includes register saving
and restoring when necessary in order to prevent register leakage
between the worlds.

Change-Id: I2d4ea993d6b11654ea0d4757d00ca20d23acf36c
Signed-off-by: Justin Chadwell <justin.chadwell@arm.com>

Makefile

@@ -510,6 +510,14 @@ ifeq ($(ENABLE_BTI),1)
     $(info Branch Protection is an experimental feature)
 endif
 
+ifeq ($(CTX_INCLUDE_MTE_REGS),1)
+    ifneq (${ARCH},aarch64)
+        $(error CTX_INCLUDE_MTE_REGS requires AArch64)
+    else
+        $(info CTX_INCLUDE_MTE_REGS is an experimental feature)
+    endif
+endif
+
 ################################################################################
 # Process platform overrideable behaviour
 ################################################################################
@@ -631,6 +639,7 @@ $(eval $(call assert_boolean,CREATE_KEYS))
 $(eval $(call assert_boolean,CTX_INCLUDE_AARCH32_REGS))
 $(eval $(call assert_boolean,CTX_INCLUDE_FPREGS))
 $(eval $(call assert_boolean,CTX_INCLUDE_PAUTH_REGS))
+$(eval $(call assert_boolean,CTX_INCLUDE_MTE_REGS))
 $(eval $(call assert_boolean,DEBUG))
 $(eval $(call assert_boolean,DYN_DISABLE_AUTH))
 $(eval $(call assert_boolean,EL3_EXCEPTION_HANDLING))
@@ -686,6 +695,7 @@ $(eval $(call add_define,CTX_INCLUDE_AARCH32_REGS))
 $(eval $(call add_define,CTX_INCLUDE_FPREGS))
 $(eval $(call add_define,CTX_INCLUDE_PAUTH_REGS))
 $(eval $(call add_define,EL3_EXCEPTION_HANDLING))
+$(eval $(call add_define,CTX_INCLUDE_MTE_REGS))
 $(eval $(call add_define,ENABLE_AMU))
 $(eval $(call add_define,ENABLE_ASSERTIONS))
 $(eval $(call add_define,ENABLE_BTI))

bl32/tsp/tsp_main.c

@@ -386,6 +386,14 @@ tsp_args_t *tsp_smc_handler(uint64_t func,
 	 */
 	tsp_get_magic(service_args);
 
+#if CTX_INCLUDE_MTE_REGS
+	/*
+	 * Write a dummy value to an MTE register, to simulate usage in the
+	 * secure world
+	 */
+	write_gcr_el1(0x99);
+#endif
+
 	/* Determine the function to perform based on the function ID */
 	switch (TSP_BARE_FID(func)) {
 	case TSP_ADD:

include/arch/aarch64/arch.h

@@ -898,4 +898,12 @@
  ******************************************************************************/
 #define SSBS			S3_3_C4_C2_6
 
+/*******************************************************************************
+ * Armv8.5 - Memory Tagging Extension Registers
+ ******************************************************************************/
+#define TFSRE0_EL1		S3_0_C5_C6_1
+#define TFSR_EL1		S3_0_C5_C6_0
+#define RGSR_EL1		S3_0_C1_C0_5
+#define GCR_EL1			S3_0_C1_C0_6
+
 #endif /* ARCH_H */

include/arch/aarch64/arch_helpers.h

@@ -501,6 +501,12 @@ DEFINE_RENAME_SYSREG_READ_FUNC(id_aa64mmfr2_el1, ID_AA64MMFR2_EL1)
 DEFINE_RENAME_SYSREG_RW_FUNCS(apiakeyhi_el1, APIAKeyHi_EL1)
 DEFINE_RENAME_SYSREG_RW_FUNCS(apiakeylo_el1, APIAKeyLo_EL1)
 
+/* Armv8.5 MTE Registers */
+DEFINE_RENAME_SYSREG_RW_FUNCS(tfsre0_el1, TFSRE0_EL1)
+DEFINE_RENAME_SYSREG_RW_FUNCS(tfsr_el1, TFSR_EL1)
+DEFINE_RENAME_SYSREG_RW_FUNCS(rgsr_el1, RGSR_EL1)
+DEFINE_RENAME_SYSREG_RW_FUNCS(gcr_el1, GCR_EL1)
+
 #define IS_IN_EL(x) \
 	(GET_EL(read_CurrentEl()) == MODE_EL##x)
 

include/lib/el3_runtime/aarch64/context.h

@@ -123,10 +123,22 @@
 #define CTX_TIMER_SYSREGS_END	CTX_AARCH32_END
 #endif /* NS_TIMER_SWITCH */
 
+#if CTX_INCLUDE_MTE_REGS
+#define CTX_TFSRE0_EL1		(CTX_TIMER_SYSREGS_END + U(0x0))
+#define CTX_TFSR_EL1		(CTX_TIMER_SYSREGS_END + U(0x8))
+#define CTX_RGSR_EL1		(CTX_TIMER_SYSREGS_END + U(0x10))
+#define CTX_GCR_EL1		(CTX_TIMER_SYSREGS_END + U(0x18))
+
+/* Align to the next 16 byte boundary */
+#define CTX_MTE_REGS_END	(CTX_TIMER_SYSREGS_END + U(0x20))
+#else
+#define CTX_MTE_REGS_END	CTX_TIMER_SYSREGS_END
+#endif /* CTX_INCLUDE_MTE_REGS */
+
 /*
  * End of system registers.
  */
-#define CTX_SYSREGS_END		CTX_TIMER_SYSREGS_END
+#define CTX_SYSREGS_END		CTX_MTE_REGS_END
 
 /*******************************************************************************
  * Constants that allow assembler code to access members of and the 'fp_regs'

lib/el3_runtime/aarch64/context.S

@@ -145,6 +145,17 @@ func el1_sysregs_context_save
 	str	x14, [x0, #CTX_CNTKCTL_EL1]
 #endif
 
+	/* Save MTE system registers if the build has instructed so */
+#if CTX_INCLUDE_MTE_REGS
+	mrs	x15, TFSRE0_EL1
+	mrs	x16, TFSR_EL1
+	stp	x15, x16, [x0, #CTX_TFSRE0_EL1]
+
+	mrs	x9, RGSR_EL1
+	mrs	x10, GCR_EL1
+	stp	x9, x10, [x0, #CTX_RGSR_EL1]
+#endif
+
 	ret
 endfunc el1_sysregs_context_save
 
@@ -229,6 +240,16 @@ func el1_sysregs_context_restore
 	ldr	x14, [x0, #CTX_CNTKCTL_EL1]
 	msr	cntkctl_el1, x14
 #endif
+	/* Restore MTE system registers if the build has instructed so */
+#if CTX_INCLUDE_MTE_REGS
+	ldp	x11, x12, [x0, #CTX_TFSRE0_EL1]
+	msr	TFSRE0_EL1, x11
+	msr	TFSR_EL1, x12
+
+	ldp	x13, x14, [x0, #CTX_RGSR_EL1]
+	msr	RGSR_EL1, x13
+	msr	GCR_EL1, x14
+#endif
 
 	/* No explict ISB required here as ERET covers it */
 	ret

lib/el3_runtime/aarch64/context_mgmt.c

@@ -137,17 +137,30 @@ void cm_setup_context(cpu_context_t *ctx, const entry_point_info_t *ep)
 		scr_el3 |= SCR_API_BIT | SCR_APK_BIT;
 #endif /* !CTX_INCLUDE_PAUTH_REGS */
 
-	unsigned int mte = get_armv8_5_mte_support();
-
 	/*
-	 * Enable MTE support unilaterally for normal world if the CPU supports
-	 * it.
+	 * Enable MTE support. Support is enabled unilaterally for the normal
+	 * world, and only for the secure world when CTX_INCLUDE_MTE_REGS is
+	 * set.
 	 */
-	if (mte != MTE_UNIMPLEMENTED) {
-		if (security_state == NON_SECURE) {
-			scr_el3 |= SCR_ATA_BIT;
-		}
+	unsigned int mte = get_armv8_5_mte_support();
+#if CTX_INCLUDE_MTE_REGS
+	assert(mte == MTE_IMPLEMENTED_ELX);
+	scr_el3 |= SCR_ATA_BIT;
+#else
+	if (mte == MTE_IMPLEMENTED_EL0) {
+		/*
+		 * Can enable MTE across both worlds as no MTE registers are
+		 * used
+		 */
+		scr_el3 |= SCR_ATA_BIT;
+	} else if (mte == MTE_IMPLEMENTED_ELX && security_state == NON_SECURE) {
+		/*
+		 * Can only enable MTE in Non-Secure world without register
+		 * saving
+		 */
+		scr_el3 |= SCR_ATA_BIT;
 	}
+#endif
 
 #ifdef IMAGE_BL31
 	/*

make_helpers/defaults.mk

@@ -214,6 +214,11 @@ ifeq (${ARCH},aarch32)
     override ENABLE_SPE_FOR_LOWER_ELS := 0
 endif
 
+# Include Memory Tagging Extension registers in cpu context. This must be set
+# to 1 if the platform wants to use this feature in the Secure world and MTE is
+# enabled at ELX.
+CTX_INCLUDE_MTE_REGS := 0
+
 ENABLE_AMU			:= 0
 
 # By default, enable Scalable Vector Extension if implemented for Non-secure