util/misc/arm64_pac_bti.S

// Copyright 2021 The Crashpad Authors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

#ifndef CRASHPAD_UTIL_MISC_ARM64_PAC_BTI_S
#define CRASHPAD_UTIL_MISC_ARM64_PAC_BTI_S

/* Support macros for the Armv8.5-A Branch Target Identification and
 * Armv8.3-A Pointer Authentication features which require emitting
 * a .note.gnu.property section with the appropriate
 * architecture-dependent feature bits set.
 * Read more: "ELF for the Arm® 64-bit Architecture"
 */
#if defined(__ARM_FEATURE_BTI_DEFAULT) && (__ARM_FEATURE_BTI_DEFAULT == 1)
#define GNU_PROPERTY_AARCH64_BTI 1  // Has BTI
#define CRASHPAD_AARCH64_VALID_JUMP_CALL_TARGET bti jc
#define CRASHPAD_AARCH64_VALID_CALL_TARGET      bti c
#define CRASHPAD_AARCH64_VALID_JUMP_TARGET      bti j
#else
#define GNU_PROPERTY_AARCH64_BTI 0  // No BTI
#define CRASHPAD_AARCH64_VALID_JUMP_CALL_TARGET
#define CRASHPAD_AARCH64_VALID_CALL_TARGET
#define CRASHPAD_AARCH64_VALID_JUMP_TARGET
#endif

#if defined(__ARM_FEATURE_PAC_DEFAULT)
#if ((__ARM_FEATURE_PAC_DEFAULT & ((1<<0)|(1<<1))) == 0)
#error Pointer authentication defines no valid key!
#endif
#define GNU_PROPERTY_AARCH64_PAC 1 // Has PAC
#else
#define GNU_PROPERTY_AARCH64_PAC 0 // No PAC
#endif

/**
 * Emit a proper .note.gnu.property section in case of PAC or BTI being enabled.
 */
#if (GNU_PROPERTY_AARCH64_BTI != 0 || GNU_PROPERTY_AARCH64_PAC != 0)
  .pushsection .note.gnu.property, "a"
  .balign 4
  .long 0x4  /* size of field "GNU" */
  .long 0x10 /* note descriptor size */
  .long 0x5  /* type of note descriptor: NT_GNU_PROPERTY_TYPE_0 */
  .asciz "GNU"
  .long 0xc0000000 /* GNU_PROPERTY_AARCH64_FEATURE_1_AND */
  .long 0x4
  .long ((GNU_PROPERTY_AARCH64_BTI<<0)|(GNU_PROPERTY_AARCH64_PAC<<1))
  .long 0x0
  .popsection
#endif

#undef GNU_PROPERTY_AARCH64_BTI
#undef GNU_PROPERTY_AARCH64_PAC

#endif /* CRASHPAD_UTIL_MISC_ARM64_PAC_BTI_S */