arm64: add prctl control for resetting ptrauth keys

Add an arm64-specific prctl to allow a thread to reinitialize its
pointer authentication keys to random values. This can be useful when
exec() is not used for starting new processes, to ensure that different
processes still have different keys.

Signed-off-by: Kristina Martsenko <kristina.martsenko@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>

2 files changed, 48 insertions, 0 deletions

diff --git a/arch/arm64/kernel/Makefile b/arch/arm64/kernel/Makefile
index 583334ce1c2c..df08d735b21d 100644
--- a/arch/arm64/kernel/Makefile
+++ b/arch/arm64/kernel/Makefile
@@ -58,6 +58,7 @@ arm64-obj-$(CONFIG_CRASH_DUMP)		+= crash_dump.o
 arm64-obj-$(CONFIG_CRASH_CORE)		+= crash_core.o
 arm64-obj-$(CONFIG_ARM_SDE_INTERFACE)	+= sdei.o
 arm64-obj-$(CONFIG_ARM64_SSBD)		+= ssbd.o
+arm64-obj-$(CONFIG_ARM64_PTR_AUTH)	+= pointer_auth.o
 
 obj-y					+= $(arm64-obj-y) vdso/ probes/
 obj-m					+= $(arm64-obj-m)
diff --git a/arch/arm64/kernel/pointer_auth.c b/arch/arm64/kernel/pointer_auth.c
new file mode 100644
index 000000000000..b9f6f5f3409a
--- /dev/null
+++ b/arch/arm64/kernel/pointer_auth.c
@@ -0,0 +1,47 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/errno.h>
+#include <linux/prctl.h>
+#include <linux/random.h>
+#include <linux/sched.h>
+#include <asm/cpufeature.h>
+#include <asm/pointer_auth.h>
+
+int ptrauth_prctl_reset_keys(struct task_struct *tsk, unsigned long arg)
+{
+	struct ptrauth_keys *keys = &tsk->thread_info.keys_user;
+	unsigned long addr_key_mask = PR_PAC_APIAKEY | PR_PAC_APIBKEY |
+				      PR_PAC_APDAKEY | PR_PAC_APDBKEY;
+	unsigned long key_mask = addr_key_mask | PR_PAC_APGAKEY;
+
+	if (!system_supports_address_auth() && !system_supports_generic_auth())
+		return -EINVAL;
+
+	if (!arg) {
+		ptrauth_keys_init(keys);
+		ptrauth_keys_switch(keys);
+		return 0;
+	}
+
+	if (arg & ~key_mask)
+		return -EINVAL;
+
+	if (((arg & addr_key_mask) && !system_supports_address_auth()) ||
+	    ((arg & PR_PAC_APGAKEY) && !system_supports_generic_auth()))
+		return -EINVAL;
+
+	if (arg & PR_PAC_APIAKEY)
+		get_random_bytes(&keys->apia, sizeof(keys->apia));
+	if (arg & PR_PAC_APIBKEY)
+		get_random_bytes(&keys->apib, sizeof(keys->apib));
+	if (arg & PR_PAC_APDAKEY)
+		get_random_bytes(&keys->apda, sizeof(keys->apda));
+	if (arg & PR_PAC_APDBKEY)
+		get_random_bytes(&keys->apdb, sizeof(keys->apdb));
+	if (arg & PR_PAC_APGAKEY)
+		get_random_bytes(&keys->apga, sizeof(keys->apga));
+
+	ptrauth_keys_switch(keys);
+
+	return 0;
+}