Add ARMv8.3-PAuth registers to CPU context

ARMv8.3-PAuth adds functionality that supports address authentication of
the contents of a register before that register is used as the target of
an indirect branch, or as a load.

This feature is supported only in AArch64 state.

This feature is mandatory in ARMv8.3 implementations.

This feature adds several registers to EL1. A new option called
CTX_INCLUDE_PAUTH_REGS has been added to select if the TF needs to save
them during Non-secure <-> Secure world switches. This option must be
enabled if the hardware has the registers or the values will be leaked
during world switches.

To prevent leaks, this patch also disables pointer authentication in the
Secure world if CTX_INCLUDE_PAUTH_REGS is 0. Any attempt to use it will
be trapped in EL3.

Change-Id: I27beba9907b9a86c6df1d0c5bf6180c972830855
Signed-off-by: Antonio Nino Diaz <antonio.ninodiaz@arm.com>

Makefile

@@ -580,6 +580,7 @@ $(eval $(call assert_boolean,COLD_BOOT_SINGLE_CPU))
 $(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,DEBUG))
 $(eval $(call assert_boolean,DYN_DISABLE_AUTH))
 $(eval $(call assert_boolean,EL3_EXCEPTION_HANDLING))
@@ -633,6 +634,7 @@ $(eval $(call add_define,ARM_ARCH_MINOR))
 $(eval $(call add_define,COLD_BOOT_SINGLE_CPU))
 $(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,ENABLE_AMU))
 $(eval $(call add_define,ENABLE_ASSERTIONS))

bl31/aarch64/ea_delegate.S

 /*
- * 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
  */
@@ -68,6 +68,10 @@ func enter_lower_el_sync_ea
 	/* Save GP registers */
 	bl	save_gp_registers
 
+#if CTX_INCLUDE_PAUTH_REGS
+	bl	pauth_context_save
+#endif
+
 	/* Setup exception class and syndrome arguments for platform handler */
 	mov	x0, #ERROR_EA_SYNC
 	mrs	x1, esr_el3
@@ -98,6 +102,10 @@ func enter_lower_el_async_ea
 	/* Save GP registers */
 	bl	save_gp_registers
 
+#if CTX_INCLUDE_PAUTH_REGS
+	bl	pauth_context_save
+#endif
+
 	/* Setup exception class and syndrome arguments for platform handler */
 	mov	x0, #ERROR_EA_ASYNC
 	mrs	x1, esr_el3

bl31/aarch64/runtime_exceptions.S

@@ -120,7 +120,13 @@
 	 * ---------------------------------------------------------------------
 	 */
 	.macro	handle_interrupt_exception label
+
 	bl	save_gp_registers
+
+#if CTX_INCLUDE_PAUTH_REGS
+	bl	pauth_context_save
+#endif
+
 	/* Save the EL3 system registers needed to return from this exception */
 	mrs	x0, spsr_el3
 	mrs	x1, elr_el3
@@ -320,14 +326,21 @@ smc_handler32:
 	tbnz	x0, #FUNCID_CC_SHIFT, smc_prohibited
 
 smc_handler64:
+	/* NOTE: The code below must preserve x0-x4 */
+
+	/* Save general purpose registers */
+	bl	save_gp_registers
+
+#if CTX_INCLUDE_PAUTH_REGS
+	bl	pauth_context_save
+#endif
+
 	/*
 	 * Populate the parameters for the SMC handler.
 	 * We already have x0-x4 in place. x5 will point to a cookie (not used
 	 * now). x6 will point to the context structure (SP_EL3) and x7 will
 	 * contain flags we need to pass to the handler.
 	 */
-	bl	save_gp_registers
-
 	mov	x5, xzr
 	mov	x6, sp
 

docs/firmware-design.rst

@@ -2558,8 +2558,13 @@ Armv8.2-A
 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.
+-  Pointer authentication features of Armv8.3-A are unconditionally enabled in
+   the Non-secure world so that lower ELs are allowed to use them without
+   causing a trap to EL3.
+
+   In order to enable the Secure world to use it, ``CTX_INCLUDE_PAUTH_REGS``
+   must be set to 1. This will add all pointer authentication system registers
+   to the context that is saved when doing a world switch.
 
 Armv7-A
 ~~~~~~~

docs/user-guide.rst

@@ -358,6 +358,12 @@ 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, will cause
+   the ARMv8.3-PAuth registers to be included when saving and restoring the CPU
+   context. Note that if the hardware supports this extension and this option is
+   set to 0 the value of the registers will be leaked between Secure and
+   Non-secure worlds. The default is 0.
+
 -  ``DEBUG``: Chooses between a debug and release build. It can take either 0
    (release) or 1 (debug) as values. 0 is the default.
 

include/arch/aarch64/arch.h

@@ -154,26 +154,22 @@
 
 #define ID_AA64PFR0_GIC_SHIFT	U(24)
 #define ID_AA64PFR0_GIC_WIDTH	U(4)
-#define ID_AA64PFR0_GIC_MASK	((ULL(1) << ID_AA64PFR0_GIC_WIDTH) - ULL(1))
+#define ID_AA64PFR0_GIC_MASK	ULL(0xf)
 
 /* 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_GPI_MASK \
-	(((ULL(1) << ID_AA64ISAR1_GPI_WIDTH) - ULL(1)) << ID_AA64ISAR1_GPI_SHIFT)
-#define ID_AA64ISAR1_GPA_MASK \
-	(((ULL(1) << ID_AA64ISAR1_GPA_WIDTH) - ULL(1)) << ID_AA64ISAR1_GPA_SHIFT)
-#define ID_AA64ISAR1_API_MASK \
-	(((ULL(1) << ID_AA64ISAR1_API_WIDTH) - ULL(1)) << ID_AA64ISAR1_API_SHIFT)
-#define ID_AA64ISAR1_APA_MASK \
-	(((ULL(1) << ID_AA64ISAR1_APA_WIDTH) - ULL(1)) << ID_AA64ISAR1_APA_SHIFT)
+#define ID_AA64ISAR1_APA_MASK	ULL(0xf)
 
 /* ID_AA64MMFR0_EL1 definitions */
 #define ID_AA64MMFR0_EL1_PARANGE_SHIFT	U(0)
@@ -258,9 +254,7 @@
 #define SCTLR_E0E_BIT		(ULL(1) << 24)
 #define SCTLR_EE_BIT		(ULL(1) << 25)
 #define SCTLR_UCI_BIT		(ULL(1) << 26)
-#define SCTLR_TRE_BIT		(ULL(1) << 28)
-#define SCTLR_AFE_BIT		(ULL(1) << 29)
-#define SCTLR_TE_BIT		(ULL(1) << 30)
+#define SCTLR_EnIA_BIT		(ULL(1) << 31)
 #define SCTLR_DSSBS_BIT		(ULL(1) << 44)
 #define SCTLR_RESET_VAL		SCTLR_EL3_RES1
 
@@ -823,7 +817,16 @@
 /*******************************************************************************
  * Armv8.3 Pointer Authentication Registers
  ******************************************************************************/
+#define APIAKeyLo_EL1		S3_0_C2_C1_0
+#define APIAKeyHi_EL1		S3_0_C2_C1_1
+#define APIBKeyLo_EL1		S3_0_C2_C1_2
+#define APIBKeyHi_EL1		S3_0_C2_C1_3
+#define APDAKeyLo_EL1		S3_0_C2_C2_0
+#define APDAKeyHi_EL1		S3_0_C2_C2_1
+#define APDBKeyLo_EL1		S3_0_C2_C2_2
+#define APDBKeyHi_EL1		S3_0_C2_C2_3
 #define APGAKeyLo_EL1		S3_0_C2_C3_0
+#define APGAKeyHi_EL1		S3_0_C2_C3_1
 
 /*******************************************************************************
  * Armv8.4 Data Independent Timing Registers

include/arch/aarch64/el3_common_macros.S

@@ -76,9 +76,16 @@
 	 * authentication instructions from lower ELs.
 	 * ---------------------------------------------------------------------
 	 */
-	mov_imm	x0, ((SCR_RESET_VAL | SCR_EA_BIT | SCR_SIF_BIT | \
-				SCR_API_BIT | SCR_APK_BIT) \
+	mov_imm	x0, ((SCR_RESET_VAL | SCR_EA_BIT | SCR_SIF_BIT) \
 			& ~(SCR_TWE_BIT | SCR_TWI_BIT | SCR_SMD_BIT))
+#if CTX_INCLUDE_PAUTH_REGS
+	/*
+	 * If the pointer authentication registers are saved during world
+	 * switches, enable pointer authentication everywhere, as it is safe to
+	 * do so.
+	 */
+	orr	x0, x0, #(SCR_API_BIT | SCR_APK_BIT)
+#endif
 	msr	scr_el3, x0
 
 	/* ---------------------------------------------------------------------

include/lib/el3_runtime/aarch64/context.h

@@ -186,6 +186,27 @@
 #define CTX_CVE_2018_3639_DISABLE	U(0)
 #define CTX_CVE_2018_3639_END		U(0x10) /* Align to the next 16 byte boundary */
 
+/*******************************************************************************
+ * Registers related to ARMv8.3-PAuth.
+ ******************************************************************************/
+#define CTX_PAUTH_REGS_OFFSET	(CTX_CVE_2018_3639_OFFSET + CTX_CVE_2018_3639_END)
+#if CTX_INCLUDE_PAUTH_REGS
+#define CTX_PACIAKEY_LO		U(0x0)
+#define CTX_PACIAKEY_HI		U(0x8)
+#define CTX_PACIBKEY_LO		U(0x10)
+#define CTX_PACIBKEY_HI		U(0x18)
+#define CTX_PACDAKEY_LO		U(0x20)
+#define CTX_PACDAKEY_HI		U(0x28)
+#define CTX_PACDBKEY_LO		U(0x30)
+#define CTX_PACDBKEY_HI		U(0x38)
+#define CTX_PACGAKEY_LO		U(0x40)
+#define CTX_PACGAKEY_HI		U(0x48)
+#define CTX_PACGAKEY_END	U(0x50)
+#define CTX_PAUTH_REGS_END	U(0x60) /* Align to the next 16 byte boundary */
+#else
+#define CTX_PAUTH_REGS_END	U(0)
+#endif /* CTX_INCLUDE_PAUTH_REGS */
+
 #ifndef __ASSEMBLY__
 
 #include <stdint.h>
@@ -210,6 +231,9 @@
 #endif
 #define CTX_EL3STATE_ALL	(CTX_EL3STATE_END >> DWORD_SHIFT)
 #define CTX_CVE_2018_3639_ALL	(CTX_CVE_2018_3639_END >> DWORD_SHIFT)
+#if CTX_INCLUDE_PAUTH_REGS
+# define CTX_PAUTH_REGS_ALL	(CTX_PAUTH_REGS_END >> DWORD_SHIFT)
+#endif
 
 /*
  * AArch64 general purpose register context structure. Usually x0-x18,
@@ -245,6 +269,11 @@ DEFINE_REG_STRUCT(el3_state, CTX_EL3STATE_ALL);
 /* Function pointer used by CVE-2018-3639 dynamic mitigation */
 DEFINE_REG_STRUCT(cve_2018_3639, CTX_CVE_2018_3639_ALL);
 
+/* Registers associated to ARMv8.3-PAuth */
+#if CTX_INCLUDE_PAUTH_REGS
+DEFINE_REG_STRUCT(pauth, CTX_PAUTH_REGS_ALL);
+#endif
+
 /*
  * Macros to access members of any of the above structures using their
  * offsets
@@ -270,6 +299,9 @@ typedef struct cpu_context {
 	fp_regs_t fpregs_ctx;
 #endif
 	cve_2018_3639_t cve_2018_3639_ctx;
+#if CTX_INCLUDE_PAUTH_REGS
+	pauth_t pauth_ctx;
+#endif
 } cpu_context_t;
 
 /* Macros to access members of the 'cpu_context_t' structure */
@@ -280,6 +312,9 @@ typedef struct cpu_context {
 #define get_sysregs_ctx(h)	(&((cpu_context_t *) h)->sysregs_ctx)
 #define get_gpregs_ctx(h)	(&((cpu_context_t *) h)->gpregs_ctx)
 #define get_cve_2018_3639_ctx(h)	(&((cpu_context_t *) h)->cve_2018_3639_ctx)
+#if CTX_INCLUDE_PAUTH_REGS
+# define get_pauth_ctx(h)	(&((cpu_context_t *) h)->pauth_ctx)
+#endif
 
 /*
  * Compile time assertions related to the 'cpu_context' structure to
@@ -298,6 +333,10 @@ CASSERT(CTX_EL3STATE_OFFSET == __builtin_offsetof(cpu_context_t, el3state_ctx),
 	assert_core_context_el3state_offset_mismatch);
 CASSERT(CTX_CVE_2018_3639_OFFSET == __builtin_offsetof(cpu_context_t, cve_2018_3639_ctx), \
 	assert_core_context_cve_2018_3639_offset_mismatch);
+#if CTX_INCLUDE_PAUTH_REGS
+CASSERT(CTX_PAUTH_REGS_OFFSET == __builtin_offsetof(cpu_context_t, pauth_ctx), \
+	assert_core_context_pauth_offset_mismatch);
+#endif
 
 /*
  * Helper macro to set the general purpose registers that correspond to

lib/el3_runtime/aarch64/context.S

@@ -13,6 +13,10 @@
 #if CTX_INCLUDE_FPREGS
 	.global	fpregs_context_save
 	.global	fpregs_context_restore
+#endif
+#if CTX_INCLUDE_PAUTH_REGS
+	.global	pauth_context_restore
+	.global	pauth_context_save
 #endif
 	.global	save_gp_registers
 	.global	restore_gp_registers
@@ -299,6 +303,76 @@ func fpregs_context_restore
 endfunc fpregs_context_restore
 #endif /* CTX_INCLUDE_FPREGS */
 
+#if CTX_INCLUDE_PAUTH_REGS
+/* -----------------------------------------------------
+ * The following function strictly follows the AArch64
+ * PCS to use x9-x17 (temporary caller-saved registers)
+ * to save the ARMv8.3-PAuth register context. It assumes
+ * that 'sp' is pointing to a 'cpu_context_t' structure
+ * to where the register context will be saved.
+ * -----------------------------------------------------
+ */
+func pauth_context_save
+	add	x11, sp, #CTX_PAUTH_REGS_OFFSET
+
+	mrs	x9, APIAKeyLo_EL1
+	mrs	x10, APIAKeyHi_EL1
+	stp	x9, x10, [x11, #CTX_PACIAKEY_LO]
+
+	mrs	x9, APIBKeyLo_EL1
+	mrs	x10, APIBKeyHi_EL1
+	stp	x9, x10, [x11, #CTX_PACIBKEY_LO]
+
+	mrs	x9, APDAKeyLo_EL1
+	mrs	x10, APDAKeyHi_EL1
+	stp	x9, x10, [x11, #CTX_PACDAKEY_LO]
+
+	mrs	x9, APDBKeyLo_EL1
+	mrs	x10, APDBKeyHi_EL1
+	stp	x9, x10, [x11, #CTX_PACDBKEY_LO]
+
+	mrs	x9, APGAKeyLo_EL1
+	mrs	x10, APGAKeyHi_EL1
+	stp	x9, x10, [x11, #CTX_PACGAKEY_LO]
+
+	ret
+endfunc pauth_context_save
+
+/* -----------------------------------------------------
+ * The following function strictly follows the AArch64
+ * PCS to use x9-x17 (temporary caller-saved registers)
+ * to restore the ARMv8.3-PAuth register context. It assumes
+ * that 'sp' is pointing to a 'cpu_context_t' structure
+ * from where the register context will be restored.
+ * -----------------------------------------------------
+ */
+func pauth_context_restore
+	add	x11, sp, #CTX_PAUTH_REGS_OFFSET
+
+	ldp	x9, x10, [x11, #CTX_PACIAKEY_LO]
+	msr	APIAKeyLo_EL1, x9
+	msr	APIAKeyHi_EL1, x10
+
+	ldp	x9, x10, [x11, #CTX_PACIAKEY_LO]
+	msr	APIBKeyLo_EL1, x9
+	msr	APIBKeyHi_EL1, x10
+
+	ldp	x9, x10, [x11, #CTX_PACDAKEY_LO]
+	msr	APDAKeyLo_EL1, x9
+	msr	APDAKeyHi_EL1, x10
+
+	ldp	x9, x10, [x11, #CTX_PACDBKEY_LO]
+	msr	APDBKeyLo_EL1, x9
+	msr	APDBKeyHi_EL1, x10
+
+	ldp	x9, x10, [x11, #CTX_PACGAKEY_LO]
+	msr	APGAKeyLo_EL1, x9
+	msr	APGAKeyHi_EL1, x10
+
+	ret
+endfunc pauth_context_restore
+#endif /* CTX_INCLUDE_PAUTH_REGS */
+
 /* -----------------------------------------------------
  * The following functions are used to save and restore
  * all the general purpose registers. Ideally we would
@@ -415,6 +489,11 @@ func el3_exit
 1:
 #endif
 
+#if CTX_INCLUDE_PAUTH_REGS
+	/* Restore ARMv8.3-PAuth registers */
+	bl	pauth_context_restore
+#endif
+
 	/* Restore saved general purpose registers and return */
 	b	restore_gp_registers_eret
 endfunc el3_exit

lib/el3_runtime/aarch64/context_mgmt.c

@@ -122,6 +122,20 @@ void cm_setup_context(cpu_context_t *ctx, const entry_point_info_t *ep)
 	scr_el3 |= SCR_FIEN_BIT;
 #endif
 
+#if !CTX_INCLUDE_PAUTH_REGS
+	/*
+	 * If the pointer authentication registers aren't saved during world
+	 * switches the value of the registers can be leaked from the Secure to
+	 * the Non-secure world. To prevent this, rather than enabling pointer
+	 * authentication everywhere, we only enable it in the Non-secure world.
+	 *
+	 * If the Secure world wants to use pointer authentication,
+	 * CTX_INCLUDE_PAUTH_REGS must be set to 1.
+	 */
+	if (security_state == NON_SECURE)
+		scr_el3 |= SCR_API_BIT | SCR_APK_BIT;
+#endif /* !CTX_INCLUDE_PAUTH_REGS */
+
 #ifdef IMAGE_BL31
 	/*
 	 * SCR_EL3.IRQ, SCR_EL3.FIQ: Enable the physical FIQ and IRQ routing as

make_helpers/defaults.mk

@@ -51,6 +51,11 @@ CTX_INCLUDE_AARCH32_REGS	:= 1
 # Include FP registers in cpu context
 CTX_INCLUDE_FPREGS		:= 0
 
+# Include pointer authentication (ARMv8.3-PAuth) registers in cpu context. This
+# must be set to 1 if the platform wants to use this feature in the Secure
+# world. It is not needed to use it in the Non-secure world.
+CTX_INCLUDE_PAUTH_REGS		:= 0
+
 # Debug build
 DEBUG				:= 0