git: 82597d2102a0 - main - arm64: Support creating a BTI & PAC note

The branch main has been updated by andrew:

URL: https://cgit.FreeBSD.org/src/commit/?id=82597d2102a02c4e9e9355717c32867d34b77ef0

commit 82597d2102a02c4e9e9355717c32867d34b77ef0
Author:     Andrew Turner <andrew@FreeBSD.org>
AuthorDate: 2023-10-10 13:00:59 +0000
Commit:     Andrew Turner <andrew@FreeBSD.org>
CommitDate: 2023-10-20 15:59:25 +0000

    arm64: Support creating a BTI & PAC note
    
    To detect when an object file is build with the Branch Target
    Identification (BTI) and Pointer Authentication Code (PAC) extensions
    there is an elf note the compiler will insert. It will only do so from
    a high level language, e.g. C or C++.
    
    To get the not in assembly add the GNU_PROPERTY_AARCH64_FEATURE_1_NOTE
    macro that can be used to create it, and the
    GNU_PROPERTY_AARCH64_FEATURE_1_VAL macro to insert the correct value
    based on which combination of BTI and PAC are enabled.
    
    Reviewed by:    markj (earlier version), emaste
    Sponsored by:   Arm Ltd
    Differential Revision:  https://reviews.freebsd.org/D42225
---
 sys/arm64/include/asm.h | 52 +++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 52 insertions(+)

diff --git a/sys/arm64/include/asm.h b/sys/arm64/include/asm.h
index 6ebfca6eaf0c..da3c3df5f647 100644
--- a/sys/arm64/include/asm.h
+++ b/sys/arm64/include/asm.h
@@ -142,6 +142,58 @@
 #define	BTI_J
 #endif
 
+/*
+ * GNU_PROPERTY_AARCH64_FEATURE_1_NOTE can be used to insert a note that
+ * the current assembly file is built with Pointer Authentication (PAC) or
+ * Branch Target Identification support (BTI). As the linker requires all
+ * object files in an executable or library to have the GNU property
+ * note to emit it in the created elf file we need to add a note to all
+ * assembly files that support BTI so the kernel and dynamic linker can
+ * mark memory used by the file as guarded.
+ *
+ * The GNU_PROPERTY_AARCH64_FEATURE_1_VAL macro encodes the combination
+ * of PAC and BTI that have been enabled. It can be used as follows:
+ * GNU_PROPERTY_AARCH64_FEATURE_1_NOTE(GNU_PROPERTY_AARCH64_FEATURE_1_VAL);
+ *
+ * To use this you need to include <sys/elf_common.h> for
+ * GNU_PROPERTY_AARCH64_FEATURE_1_*
+ */
+#if defined(__ARM_FEATURE_BTI_DEFAULT)
+#if defined(__ARM_FEATURE_PAC_DEFAULT)
+/* BTI, PAC */
+#define	GNU_PROPERTY_AARCH64_FEATURE_1_VAL				\
+    (GNU_PROPERTY_AARCH64_FEATURE_1_BTI | GNU_PROPERTY_AARCH64_FEATURE_1_PAC)
+#else
+/* BTI, no PAC */
+#define	GNU_PROPERTY_AARCH64_FEATURE_1_VAL				\
+    (GNU_PROPERTY_AARCH64_FEATURE_1_BTI)
+#endif
+#elif defined(__ARM_FEATURE_PAC_DEFAULT)
+/* No BTI, PAC */
+#define	GNU_PROPERTY_AARCH64_FEATURE_1_VAL				\
+    (GNU_PROPERTY_AARCH64_FEATURE_1_PAC)
+#else
+/* No BTI, no PAC */
+#define	GNU_PROPERTY_AARCH64_FEATURE_1_VAL	0
+#endif
+
+#if defined(__ARM_FEATURE_BTI_DEFAULT) || defined(__ARM_FEATURE_PAC_DEFAULT)
+#define	GNU_PROPERTY_AARCH64_FEATURE_1_NOTE(x)				\
+    .section .note.gnu.property, "a";					\
+    .balign 8;								\
+    .4byte 0x4;				/* sizeof(vendor) */		\
+    .4byte 0x10;			/* sizeof(note data) */		\
+    .4byte (NT_GNU_PROPERTY_TYPE_0);					\
+    .asciz "GNU";			/* vendor */			\
+    /* note data: */							\
+    .4byte (GNU_PROPERTY_AARCH64_FEATURE_1_AND);			\
+    .4byte 0x4;				/* sizeof(property) */		\
+    .4byte (x);				/* property */			\
+    .4byte 0
+#else
+#define	GNU_PROPERTY_AARCH64_FEATURE_1_NOTE(x)
+#endif
+
 #endif /* _MACHINE_ASM_H_ */
 
 #endif /* !__arm__ */