[RFC 15/17] arm64: enable ptrauth earlier

[Kristina Martsenko <kristina.martsenko@arm.com>]

When the kernel is compiled with pointer auth instructions, the boot CPU
needs to start using pointer auth very early, so change the cpucap to
account for this.

A function that enables pointer auth cannot return, so inline such
functions or compile them without pointer auth.

Do not use the cpu_enable callback, to avoid compiling the whole
callchain down to cpu_enable without pointer auth.

Note the change in behavior: if the boot CPU has pointer auth and a late
CPU does not, we panic. Until now we would have just disabled pointer
auth in this case.

Signed-off-by: Kristina Martsenko <kristina.martsenko@arm.com>
---
 arch/arm64/include/asm/cpufeature.h   |  9 +++++++++
 arch/arm64/include/asm/pointer_auth.h | 18 ++++++++++++++++++
 arch/arm64/kernel/cpufeature.c        | 14 ++++----------
 arch/arm64/kernel/smp.c               |  7 ++++++-
 4 files changed, 37 insertions(+), 11 deletions(-)

diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
index 1717ba1db35d..af4ca92a5fa9 100644
--- a/arch/arm64/include/asm/cpufeature.h
+++ b/arch/arm64/include/asm/cpufeature.h
@@ -292,6 +292,15 @@ extern struct arm64_ftr_reg arm64_ftr_reg_ctrel0;
  */
 #define ARM64_CPUCAP_STRICT_BOOT_CPU_FEATURE ARM64_CPUCAP_SCOPE_BOOT_CPU
 
+/*
+ * CPU feature used early in the boot based on the boot CPU. It is safe for a
+ * late CPU to have this feature even though the boot CPU hasn't enabled it,
+ * although the feature will not be used by Linux in this case. If the boot CPU
+ * has enabled this feature already, then every late CPU must have it.
+ */
+#define ARM64_CPUCAP_BOOT_CPU_FEATURE			\
+	 (ARM64_CPUCAP_SCOPE_BOOT_CPU | ARM64_CPUCAP_PERMITTED_FOR_LATE_CPU)
+
 struct arm64_cpu_capabilities {
 	const char *desc;
 	u16 capability;
diff --git a/arch/arm64/include/asm/pointer_auth.h b/arch/arm64/include/asm/pointer_auth.h
index e60f225d9fa2..0634f06c3af2 100644
--- a/arch/arm64/include/asm/pointer_auth.h
+++ b/arch/arm64/include/asm/pointer_auth.h
@@ -11,6 +11,13 @@
 
 #ifdef CONFIG_ARM64_PTR_AUTH
 /*
+ * Compile the function without pointer authentication instructions. This
+ * allows pointer authentication to be enabled/disabled within the function
+ * (but leaves the function unprotected by pointer authentication).
+ */
+#define __no_ptrauth	__attribute__((target("sign-return-address=none")))
+
+/*
  * Each key is a 128-bit quantity which is split across a pair of 64-bit
  * registers (Lo and Hi).
  */
@@ -51,6 +58,15 @@ static inline void ptrauth_keys_switch(struct ptrauth_keys *keys)
 	__ptrauth_key_install(APIA, keys->apia);
 }
 
+static __always_inline void ptrauth_cpu_enable(void)
+{
+	if (!cpus_have_const_cap(ARM64_HAS_ADDRESS_AUTH))
+		return;
+
+	sysreg_clear_set(sctlr_el1, 0, SCTLR_ELx_ENIA);
+	isb();
+}
+
 /*
  * The EL0 pointer bits used by a pointer authentication code.
  * This is dependent on TBI0 being enabled, or bits 63:56 would also apply.
@@ -71,8 +87,10 @@ static inline unsigned long ptrauth_strip_insn_pac(unsigned long ptr)
 	ptrauth_keys_init(&(tsk)->thread_info.keys_user)
 
 #else /* CONFIG_ARM64_PTR_AUTH */
+#define __no_ptrauth
 #define ptrauth_strip_insn_pac(lr)	(lr)
 #define ptrauth_task_init_user(tsk)
+#define ptrauth_cpu_enable(tsk)
 #endif /* CONFIG_ARM64_PTR_AUTH */
 
 #endif /* __ASM_POINTER_AUTH_H */
diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index 3157685aa56a..380ee01145e8 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -1040,15 +1040,10 @@ static void cpu_has_fwb(const struct arm64_cpu_capabilities *__unused)
 }
 
 #ifdef CONFIG_ARM64_PTR_AUTH
-static void cpu_enable_address_auth(struct arm64_cpu_capabilities const *cap)
-{
-	sysreg_clear_set(sctlr_el1, 0, SCTLR_ELx_ENIA);
-}
-
 static bool has_address_auth(const struct arm64_cpu_capabilities *entry,
 			     int __unused)
 {
-	u64 isar1 = read_sanitised_ftr_reg(SYS_ID_AA64ISAR1_EL1);
+	u64 isar1 = read_sysreg(id_aa64isar1_el1);
 	bool api, apa;
 
 	apa = cpuid_feature_extract_unsigned_field(isar1,
@@ -1251,7 +1246,7 @@ static const struct arm64_cpu_capabilities arm64_features[] = {
 	{
 		.desc = "Address authentication (architected algorithm)",
 		.capability = ARM64_HAS_ADDRESS_AUTH_ARCH,
-		.type = ARM64_CPUCAP_SYSTEM_FEATURE,
+		.type = ARM64_CPUCAP_BOOT_CPU_FEATURE,
 		.sys_reg = SYS_ID_AA64ISAR1_EL1,
 		.sign = FTR_UNSIGNED,
 		.field_pos = ID_AA64ISAR1_APA_SHIFT,
@@ -1261,7 +1256,7 @@ static const struct arm64_cpu_capabilities arm64_features[] = {
 	{
 		.desc = "Address authentication (IMP DEF algorithm)",
 		.capability = ARM64_HAS_ADDRESS_AUTH_IMP_DEF,
-		.type = ARM64_CPUCAP_SYSTEM_FEATURE,
+		.type = ARM64_CPUCAP_BOOT_CPU_FEATURE,
 		.sys_reg = SYS_ID_AA64ISAR1_EL1,
 		.sign = FTR_UNSIGNED,
 		.field_pos = ID_AA64ISAR1_API_SHIFT,
@@ -1270,9 +1265,8 @@ static const struct arm64_cpu_capabilities arm64_features[] = {
 	},
 	{
 		.capability = ARM64_HAS_ADDRESS_AUTH,
-		.type = ARM64_CPUCAP_SYSTEM_FEATURE,
+		.type = ARM64_CPUCAP_BOOT_CPU_FEATURE,
 		.matches = has_address_auth,
-		.cpu_enable = cpu_enable_address_auth,
 	},
 #endif /* CONFIG_ARM64_PTR_AUTH */
 	{},
diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
index 25fcd22a4bb2..09690024dce8 100644
--- a/arch/arm64/kernel/smp.c
+++ b/arch/arm64/kernel/smp.c
@@ -53,6 +53,7 @@
 #include <asm/numa.h>
 #include <asm/pgtable.h>
 #include <asm/pgalloc.h>
+#include <asm/pointer_auth.h>
 #include <asm/processor.h>
 #include <asm/smp_plat.h>
 #include <asm/sections.h>
@@ -211,6 +212,8 @@ asmlinkage notrace void secondary_start_kernel(void)
 	 */
 	check_local_cpu_capabilities();
 
+	ptrauth_cpu_enable();
+
 	if (cpu_ops[cpu]->cpu_postboot)
 		cpu_ops[cpu]->cpu_postboot();
 
@@ -405,7 +408,7 @@ void __init smp_cpus_done(unsigned int max_cpus)
 	mark_linear_text_alias_ro();
 }
 
-void __init smp_prepare_boot_cpu(void)
+void __init __no_ptrauth smp_prepare_boot_cpu(void)
 {
 	set_my_cpu_offset(per_cpu_offset(smp_processor_id()));
 	/*
@@ -414,6 +417,8 @@ void __init smp_prepare_boot_cpu(void)
 	 */
 	jump_label_init();
 	cpuinfo_store_boot_cpu();
+
+	ptrauth_cpu_enable();
 }
 
 static u64 __init of_get_cpu_mpidr(struct device_node *dn)
-- 
2.11.0