csu: Teach csu about PAC and BTI

Add the Branch Target Identification (BTI) note to libc assembly
sources and Pointer Authentication Code (PAC) instructions to _init and
_fini.

_init and _fini may be called indirectly so need a BTI landing pad. As
they are non-leaf functions use the appropriate PAC instruction that
also guards against changing the link register.

As all object files need the note for any binary using these object files
we need to insert it in all asm files.

Reviewed by:	markj
Sponsored by:	Arm Ltd
Differential Revision:	https://reviews.freebsd.org/D42227

lib/csu/aarch64/crt1_s.S

@@ -30,6 +30,8 @@
  */
 
 #include <machine/asm.h>
+#include <sys/elf_common.h>
+
 	/*
 	 * The program entry point
 	 * void _start(char **ap, void (*cleanup)(void)) __dead2
@@ -62,3 +64,5 @@ eprol:
 END(_start)
 
 	.section .note.GNU-stack,"",@progbits
+
+GNU_PROPERTY_AARCH64_FEATURE_1_NOTE(GNU_PROPERTY_AARCH64_FEATURE_1_VAL)

lib/csu/aarch64/crti.S

@@ -28,11 +28,14 @@
  */
 
 #include <machine/asm.h>
+#include <sys/elf_common.h>
+
 	.section .init,"ax",@progbits
 	.align 4
 	.globl	_init
 	.type	_init,@function
 _init:
+	PAC_LR_SIGN
 	stp	x29, x30, [sp, #-16]!
 	mov	x29, sp
 
@@ -41,6 +44,8 @@ _init:
 	.globl	_fini
 	.type	_fini,@function
 _fini:
+	PAC_LR_SIGN
 	stp	x29, x30, [sp, #-16]!
 	mov	x29, sp
 
+GNU_PROPERTY_AARCH64_FEATURE_1_NOTE(GNU_PROPERTY_AARCH64_FEATURE_1_VAL)

lib/csu/aarch64/crtn.S

@@ -28,13 +28,19 @@
  */
 
 #include <machine/asm.h>
+#include <sys/elf_common.h>
+
 	.section .init,"ax",@progbits
 	ldp	x29, x30, [sp], #16
+	PAC_LR_AUTH
 	ret
 
 
 	.section .fini,"ax",@progbits
 	ldp	x29, x30, [sp], #16
+	PAC_LR_AUTH
 	ret
 
 	.section .note.GNU-stack,"",%progbits
+
+GNU_PROPERTY_AARCH64_FEATURE_1_NOTE(GNU_PROPERTY_AARCH64_FEATURE_1_VAL)

lib/csu/common/crtbrand.S

@@ -47,3 +47,8 @@
 4:
 
 	.section .note.GNU-stack,"",%progbits
+
+#ifdef __aarch64__
+/* This is needed in all objects for BTI to be used in the linked elf file */
+GNU_PROPERTY_AARCH64_FEATURE_1_NOTE(GNU_PROPERTY_AARCH64_FEATURE_1_VAL)
+#endif

lib/csu/common/feature_note.S

@@ -40,3 +40,8 @@
 4:
 
 	.section .note.GNU-stack,"",%progbits
+
+#ifdef __aarch64__
+/* This is needed in all objects for BTI to be used in the linked elf file */
+GNU_PROPERTY_AARCH64_FEATURE_1_NOTE(GNU_PROPERTY_AARCH64_FEATURE_1_VAL)
+#endif

lib/csu/common/ignore_init_note.S

@@ -41,3 +41,8 @@
 4:
 
 	.section .note.GNU-stack,"",%progbits
+
+#ifdef __aarch64__
+/* This is needed in all objects for BTI to be used in the linked elf file */
+GNU_PROPERTY_AARCH64_FEATURE_1_NOTE(GNU_PROPERTY_AARCH64_FEATURE_1_VAL)
+#endif