[PATCH v2 1/6] armv8: Disable pointer authentication traps for EL1

[Peter Hoyes]

From: Peter Hoyes <Peter.Hoyes at arm.com>

The use of ARMv8.3 pointer authentication (PAuth) is governed by fields
in HCR_EL2, which trigger a 'trap to EL2' if not enabled. The reset
value of these fields is 'architecturally unknown' so we must ensure
that the fields are enabled (to disable the traps) if we are entering
the kernel at EL1.

The APK field disables PAuth instruction traps and the API field
disables PAuth register traps

Add code to disable the traps in armv8_switch_to_el1_m. Prior to doing
so, it checks fields in the ID_AA64ISAR1_EL1 register to ensure pointer
authentication is supported by the hardware.

The runtime checks require a second temporary register, so add this to
the EL1 transition macro signature and update 2 call sites.

Signed-off-by: Peter Hoyes <Peter.Hoyes at arm.com>
---
 arch/arm/cpu/armv8/fsl-layerscape/spintable.S |  2 +-
 arch/arm/cpu/armv8/transition.S               |  2 +-
 arch/arm/include/asm/macro.h                  | 11 +++++++++--
 arch/arm/include/asm/system.h                 | 15 +++++++++++++++
 4 files changed, 26 insertions(+), 4 deletions(-)

diff --git a/arch/arm/cpu/armv8/fsl-layerscape/spintable.S b/arch/arm/cpu/armv8/fsl-layerscape/spintable.S
index 363ded03e6..d6bd188459 100644
--- a/arch/arm/cpu/armv8/fsl-layerscape/spintable.S
+++ b/arch/arm/cpu/armv8/fsl-layerscape/spintable.S
@@ -93,7 +93,7 @@ __secondary_boot_func:
 4:
 #ifdef CONFIG_ARMV8_SWITCH_TO_EL1
 	switch_el x7, _dead_loop, 0f, _dead_loop
-0:	armv8_switch_to_el1_m x4, x6, x7
+0:	armv8_switch_to_el1_m x4, x6, x7, x9
 #else
 	switch_el x7, 0f, _dead_loop, _dead_loop
 0:	armv8_switch_to_el2_m x4, x6, x7
diff --git a/arch/arm/cpu/armv8/transition.S b/arch/arm/cpu/armv8/transition.S
index a31af4ffc8..9dbdff3a4f 100644
--- a/arch/arm/cpu/armv8/transition.S
+++ b/arch/arm/cpu/armv8/transition.S
@@ -40,7 +40,7 @@ ENTRY(armv8_switch_to_el1)
 	 * now, jump to the address saved in x4.
 	 */
 	br x4
-1:	armv8_switch_to_el1_m x4, x5, x6
+1:	armv8_switch_to_el1_m x4, x5, x6, x7
 ENDPROC(armv8_switch_to_el1)
 .popsection
 
diff --git a/arch/arm/include/asm/macro.h b/arch/arm/include/asm/macro.h
index 485310d660..e1eefc283f 100644
--- a/arch/arm/include/asm/macro.h
+++ b/arch/arm/include/asm/macro.h
@@ -256,7 +256,7 @@ lr	.req	x30
  * For loading 64-bit OS, x0 is physical address to the FDT blob.
  * They will be passed to the guest.
  */
-.macro armv8_switch_to_el1_m, ep, flag, tmp
+.macro armv8_switch_to_el1_m, ep, flag, tmp, tmp2
 	/* Initialize Generic Timers */
 	mrs	\tmp, cnthctl_el2
 	/* Enable EL1 access to timers */
@@ -306,7 +306,14 @@ lr	.req	x30
 	b.eq	1f
 
 	/* Initialize HCR_EL2 */
-	ldr	\tmp, =(HCR_EL2_RW_AARCH64 | HCR_EL2_HCD_DIS)
+	/* Only disable PAuth traps if PAuth is supported */
+	mrs	\tmp, id_aa64isar1_el1
+	ldr	\tmp2, =(ID_AA64ISAR1_EL1_GPI | ID_AA64ISAR1_EL1_GPA | \
+		      ID_AA64ISAR1_EL1_API | ID_AA64ISAR1_EL1_APA)
+	tst	\tmp, \tmp2
+	mov	\tmp2, #(HCR_EL2_RW_AARCH64 | HCR_EL2_HCD_DIS)
+	orr	\tmp, \tmp2, #(HCR_EL2_APK | HCR_EL2_API)
+	csel	\tmp, \tmp2, \tmp, eq
 	msr	hcr_el2, \tmp
 
 	/* Return to the EL1_SP1 mode from EL2 */
diff --git a/arch/arm/include/asm/system.h b/arch/arm/include/asm/system.h
index 8b3a54e64c..77aa18909e 100644
--- a/arch/arm/include/asm/system.h
+++ b/arch/arm/include/asm/system.h
@@ -75,10 +75,25 @@
 /*
  * HCR_EL2 bits definitions
  */
+#define HCR_EL2_API		(1 << 41) /* Trap pointer authentication
+				             instructions                     */
+#define HCR_EL2_APK		(1 << 40) /* Trap pointer authentication
+				             key access                       */
 #define HCR_EL2_RW_AARCH64	(1 << 31) /* EL1 is AArch64                   */
 #define HCR_EL2_RW_AARCH32	(0 << 31) /* Lower levels are AArch32         */
 #define HCR_EL2_HCD_DIS		(1 << 29) /* Hypervisor Call disabled         */
 
+/*
+ * ID_AA64ISAR1_EL1 bits definitions
+ */
+#define ID_AA64ISAR1_EL1_GPI	(0xF << 28) /* Implementation-defined generic
+				               code auth algorithm            */
+#define ID_AA64ISAR1_EL1_GPA	(0xF << 24) /* QARMA generic code auth
+				               algorithm                      */
+#define ID_AA64ISAR1_EL1_API	(0xF << 8)  /* Implementation-defined address
+				               auth algorithm                 */
+#define ID_AA64ISAR1_EL1_APA	(0xF << 4)  /* QARMA address auth algorithm   */
+
 /*
  * ID_AA64PFR0_EL1 bits definitions
  */
-- 
2.25.1