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arm64: Support creating a BTI & PAC note

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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
This commit is contained in:
Andrew Turner 2023-10-10 14:00:59 +01:00
parent ceefd491c7
commit 82597d2102
1 changed files with 52 additions and 0 deletions
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52
sys/arm64/include/asm.h
View file

@ -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__ */