arm64: add basic pointer authentication support

This patch adds basic support for pointer authentication, allowing
userspace to make use of APIAKey, APIBKey, APDAKey, APDBKey, and
APGAKey. The kernel maintains key values for each process (shared by all
threads within), which are initialised to random values at exec() time.

The ID_AA64ISAR1_EL1.{APA,API,GPA,GPI} fields are exposed to userspace,
to describe that pointer authentication instructions are available and
that the kernel is managing the keys. Two new hwcaps are added for the
same reason: PACA (for address authentication) and PACG (for generic
authentication).

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Kristina Martsenko <kristina.martsenko@arm.com>
Tested-by: Adam Wallis <awallis@codeaurora.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Ramana Radhakrishnan <ramana.radhakrishnan@arm.com>
Cc: Suzuki K Poulose <suzuki.poulose@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
[will: Fix sizeof() usage and unroll address key initialisation]
Signed-off-by: Will Deacon <will.deacon@arm.com>

1 files changed, 79 insertions, 0 deletions

diff --git a/arch/arm64/include/asm/pointer_auth.h b/arch/arm64/include/asm/pointer_auth.h
new file mode 100644
index 000000000000..91c4185dda5b
--- /dev/null
+++ b/arch/arm64/include/asm/pointer_auth.h
@@ -0,0 +1,79 @@
+// SPDX-License-Identifier: GPL-2.0
+#ifndef __ASM_POINTER_AUTH_H
+#define __ASM_POINTER_AUTH_H
+
+#include <linux/random.h>
+
+#include <asm/cpufeature.h>
+#include <asm/sysreg.h>
+
+#ifdef CONFIG_ARM64_PTR_AUTH
+/*
+ * Each key is a 128-bit quantity which is split across a pair of 64-bit
+ * registers (Lo and Hi).
+ */
+struct ptrauth_key {
+	unsigned long lo, hi;
+};
+
+/*
+ * We give each process its own keys, which are shared by all threads. The keys
+ * are inherited upon fork(), and reinitialised upon exec*().
+ */
+struct ptrauth_keys {
+	struct ptrauth_key apia;
+	struct ptrauth_key apib;
+	struct ptrauth_key apda;
+	struct ptrauth_key apdb;
+	struct ptrauth_key apga;
+};
+
+static inline void ptrauth_keys_init(struct ptrauth_keys *keys)
+{
+	if (system_supports_address_auth()) {
+		get_random_bytes(&keys->apia, sizeof(keys->apia));
+		get_random_bytes(&keys->apib, sizeof(keys->apib));
+		get_random_bytes(&keys->apda, sizeof(keys->apda));
+		get_random_bytes(&keys->apdb, sizeof(keys->apdb));
+	}
+
+	if (system_supports_generic_auth())
+		get_random_bytes(&keys->apga, sizeof(keys->apga));
+}
+
+#define __ptrauth_key_install(k, v)				\
+do {								\
+	struct ptrauth_key __pki_v = (v);			\
+	write_sysreg_s(__pki_v.lo, SYS_ ## k ## KEYLO_EL1);	\
+	write_sysreg_s(__pki_v.hi, SYS_ ## k ## KEYHI_EL1);	\
+} while (0)
+
+static inline void ptrauth_keys_switch(struct ptrauth_keys *keys)
+{
+	if (system_supports_address_auth()) {
+		__ptrauth_key_install(APIA, keys->apia);
+		__ptrauth_key_install(APIB, keys->apib);
+		__ptrauth_key_install(APDA, keys->apda);
+		__ptrauth_key_install(APDB, keys->apdb);
+	}
+
+	if (system_supports_generic_auth())
+		__ptrauth_key_install(APGA, keys->apga);
+}
+
+#define ptrauth_thread_init_user(tsk)					\
+do {									\
+	struct task_struct *__ptiu_tsk = (tsk);				\
+	ptrauth_keys_init(&__ptiu_tsk->thread_info.keys_user);		\
+	ptrauth_keys_switch(&__ptiu_tsk->thread_info.keys_user);	\
+} while (0)
+
+#define ptrauth_thread_switch(tsk)	\
+	ptrauth_keys_switch(&(tsk)->thread_info.keys_user)
+
+#else /* CONFIG_ARM64_PTR_AUTH */
+#define ptrauth_thread_init_user(tsk)
+#define ptrauth_thread_switch(tsk)
+#endif /* CONFIG_ARM64_PTR_AUTH */
+
+#endif /* __ASM_POINTER_AUTH_H */