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>

arch/arm64/include/asm/processor.h

@@ -44,6 +44,7 @@
 #include <asm/hw_breakpoint.h>
 #include <asm/lse.h>
 #include <asm/pgtable-hwdef.h>
+#include <asm/pointer_auth.h>
 #include <asm/ptrace.h>
 #include <asm/types.h>
 
@@ -289,6 +290,9 @@ extern void __init minsigstksz_setup(void);
 #define SVE_SET_VL(arg)	sve_set_current_vl(arg)
 #define SVE_GET_VL()	sve_get_current_vl()
 
+/* PR_PAC_RESET_KEYS prctl */
+#define PAC_RESET_KEYS(tsk, arg)	ptrauth_prctl_reset_keys(tsk, arg)
+
 /*
  * For CONFIG_GCC_PLUGIN_STACKLEAK
  *