Merge pull request #1641 from jeenu-arm/ptrauth

AArch64: Enable lower ELs to use pointer authentication

docs/firmware-design.rst

@@ -2532,6 +2532,12 @@ This Architecture Extension is targeted when ``ARM_ARCH_MAJOR`` == 8 and
    translation table entries for a given stage of translation for a particular
    translation regime.
 
+Armv8.3-A
+~~~~~~~~~
+
+-  Pointer Authentication features of Armv8.3-A are unconditionally enabled so
+   that lower ELs are allowed to use them without causing a trap to EL3.
+
 Armv7-A
 ~~~~~~~
 

include/common/aarch64/el3_common_macros.S

@@ -70,9 +70,14 @@
 	 *
 	 * SCR_EL3.EA: Set to one to route External Aborts and SError Interrupts
 	 *  to EL3 when executing at any EL.
+	 *
+	 * SCR_EL3.{API,APK}: For Armv8.3 pointer authentication feature,
+	 * disable traps to EL3 when accessing key registers or using pointer
+	 * authentication instructions from lower ELs.
 	 * ---------------------------------------------------------------------
 	 */
-	mov	x0, #((SCR_RESET_VAL | SCR_EA_BIT | SCR_SIF_BIT) \
+	mov_imm	x0, ((SCR_RESET_VAL | SCR_EA_BIT | SCR_SIF_BIT | \
+				SCR_API_BIT | SCR_APK_BIT) \
 			& ~(SCR_TWE_BIT | SCR_TWI_BIT | SCR_SMD_BIT))
 	msr	scr_el3, x0
 

include/lib/aarch64/arch.h

@@ -218,6 +218,8 @@
 /* SCR definitions */
 #define SCR_RES1_BITS		((U(1) << 4) | (U(1) << 5))
 #define SCR_FIEN_BIT		(U(1) << 21)
+#define SCR_API_BIT		(U(1) << 17)
+#define SCR_APK_BIT		(U(1) << 16)
 #define SCR_TWE_BIT		(U(1) << 13)
 #define SCR_TWI_BIT		(U(1) << 12)
 #define SCR_ST_BIT		(U(1) << 11)
@@ -274,6 +276,8 @@
 #define VTTBR_BADDR_SHIFT	U(0)
 
 /* HCR definitions */
+#define HCR_API_BIT		(ULL(1) << 41)
+#define HCR_APK_BIT		(ULL(1) << 40)
 #define HCR_RW_SHIFT		U(31)
 #define HCR_RW_BIT		(ULL(1) << HCR_RW_SHIFT)
 #define HCR_AMO_BIT		(ULL(1) << 5)

lib/el3_runtime/aarch64/context_mgmt.c

@@ -290,6 +290,7 @@ void cm_prepare_el3_exit(uint32_t security_state)
 	uint32_t sctlr_elx, scr_el3, mdcr_el2;
 	cpu_context_t *ctx = cm_get_context(security_state);
 	int el2_unused = 0;
+	uint64_t hcr_el2 = 0;
 
 	assert(ctx);
 
@@ -309,13 +310,20 @@ void cm_prepare_el3_exit(uint32_t security_state)
 			 * EL2 present but unused, need to disable safely.
 			 * SCTLR_EL2 can be ignored in this case.
 			 *
-			 * Initialise all fields in HCR_EL2, except HCR_EL2.RW,
-			 * to zero so that Non-secure operations do not trap to
-			 * EL2.
-			 *
-			 * HCR_EL2.RW: Set this field to match SCR_EL3.RW
+			 * Set EL2 register width appropriately: Set HCR_EL2
+			 * field to match SCR_EL3.RW.
 			 */
-			write_hcr_el2((scr_el3 & SCR_RW_BIT) ? HCR_RW_BIT : 0);
+			if (scr_el3 & SCR_RW_BIT)
+				hcr_el2 |= HCR_RW_BIT;
+
+			/*
+			 * For Armv8.3 pointer authentication feature, disable
+			 * traps to EL2 when accessing key registers or using
+			 * pointer authentication instructions from lower ELs.
+			 */
+			hcr_el2 |= (HCR_API_BIT | HCR_APK_BIT);
+
+			write_hcr_el2(hcr_el2);
 
 			/*
 			 * Initialise CPTR_EL2 setting all fields rather than