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[DRAFT] gh-128605: Add branch protections for aarch64 in asm_trampoline.S #130864

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[DRAFT] gh-128605: Add branch protections for aarch64 in asm_trampoline.S #130864

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4 changes: 4 additions & 0 deletions Python/asm_trampoline.S
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Original file line number Diff line number Diff line change
@@ -1,3 +1,5 @@
#include "asm_trampoline_aarch64.h"

.text
.globl _Py_trampoline_func_start
# The following assembly is equivalent to:
Expand All @@ -20,10 +22,12 @@ _Py_trampoline_func_start:
#if defined(__aarch64__) && defined(__AARCH64EL__) && !defined(__ILP32__)
// ARM64 little endian, 64bit ABI
// generate with aarch64-linux-gnu-gcc 12.1
SIGN_LR
stp x29, x30, [sp, -16]!
mov x29, sp
blr x3
ldp x29, x30, [sp], 16
VERIFY_LR
ret
#endif
#ifdef __riscv
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50 changes: 50 additions & 0 deletions Python/asm_trampoline_aarch64.h
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Original file line number Diff line number Diff line change
@@ -0,0 +1,50 @@
#ifndef ASM_TRAMPOLINE_AARCH_64_H_
#define ASM_TRAMPOLINE_AARCH_64_H_

/*
* References:
* - https://developer.arm.com/documentation/101028/0012/5--Feature-test-macros
* - https://github.com/ARM-software/abi-aa/blob/main/aaelf64/aaelf64.rst
*/

#if defined(__ARM_FEATURE_BTI_DEFAULT) && __ARM_FEATURE_BTI_DEFAULT == 1
#define BTI_J hint 36 /* bti j: for jumps, IE br instructions */
#define BTI_C hint 34 /* bti c: for calls, IE bl instructions */
#define GNU_PROPERTY_AARCH64_BTI 1 /* bit 0 GNU Notes is for BTI support */
#else
#define BTI_J
#define BTI_C
#define GNU_PROPERTY_AARCH64_BTI 0
#endif

#if defined(__ARM_FEATURE_PAC_DEFAULT)
#if __ARM_FEATURE_PAC_DEFAULT & 1
#define SIGN_LR hint 25 /* paciasp: sign with the A key */
#define VERIFY_LR hint 29 /* autiasp: verify with the A key */
#elif __ARM_FEATURE_PAC_DEFAULT & 2
#define SIGN_LR hint 27 /* pacibsp: sign with the b key */
#define VERIFY_LR hint 31 /* autibsp: verify with the b key */
#endif
#define GNU_PROPERTY_AARCH64_POINTER_AUTH 2 /* bit 1 GNU Notes is for PAC support */
#else
#define SIGN_LR BTI_C
#define VERIFY_LR
#define GNU_PROPERTY_AARCH64_POINTER_AUTH 0
#endif

/* Add the BTI and PAC support to GNU Notes section */
#if GNU_PROPERTY_AARCH64_BTI != 0 || GNU_PROPERTY_AARCH64_POINTER_AUTH != 0
.pushsection .note.gnu.property, "a"; /* Start a new allocatable section */
.balign 8; /* align it on a byte boundry */
.long 4; /* size of "GNU\0" */
.long 0x10; /* size of descriptor */
.long 0x5; /* NT_GNU_PROPERTY_TYPE_0 */
.asciz "GNU";
.long 0xc0000000; /* GNU_PROPERTY_AARCH64_FEATURE_1_AND */
.long 4; /* Four bytes of data */
.long (GNU_PROPERTY_AARCH64_BTI|GNU_PROPERTY_AARCH64_POINTER_AUTH); /* BTI or PAC is enabled */
.long 0; /* padding for 8 byte alignment */
.popsection; /* end the section */
#endif

#endif
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