TheRock/compiler/amd-llvm/compiler-rt/test/builtins/Unit/aarch64/emupac.c

// REQUIRES: librt_has_emupac
// RUN: %clang_builtins %s %librt -o %t
// RUN: %run %t 1
// RUN: %run %t 2
// RUN: %expect_crash %run %t 3
// RUN: %expect_crash %run %t 4

#include <stdbool.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>

uint64_t __emupac_pacda(uint64_t ptr, uint64_t disc);
uint64_t __emupac_autda(uint64_t ptr, uint64_t disc);

static bool pac_supported() {
  register uintptr_t x30 __asm__("x30") = 1ULL << 55;
  __asm__ __volatile__("xpaclri" : "+r"(x30));
  return x30 & (1ULL << 54);
}

static bool fpac_supported(uint64_t ap) {
  // The meaning of values larger than 6 is reserved as of July 2025; in theory
  // larger values could mean that FEAT_FPAC is not implemented.
  return ap == 4 || ap == 5 || ap == 6;
}

// The crash tests would fail to crash (causing the test to fail) if:
// - The operating system did not enable the DA key, or
// - The CPU supports FEAT_PAuth but not FEAT_FPAC.
// Therefore, they call this function, which will crash the test process if one
// of these cases is detected so that %expect_crash detects the crash and causes
// the test to pass.
//
// We detect the former case by attempting to sign a pointer. If the signed
// pointer is equal to the unsigned pointer, DA is likely disabled, so we crash.
//
// We detect the latter case by reading ID_AA64ISAR1_EL1 and ID_AA64ISAR2_EL1.
// It is expected that the operating system will either trap and emulate reading
// the system registers (as Linux does) or crash the process. In the
// trap/emulate case we check the APA, API and APA3 fields for FEAT_FPAC support
// and crash if it is not available. In the crash case we will crash when
// reading the register leading to a passing test. This means that operating
// systems with the crashing behavior do not support the crash tests.
static void crash_if_crash_tests_unsupported() {
  if (!pac_supported())
    return;

  uint64_t ptr = 0;
  __asm__ __volatile__(".arch_extension pauth\npacda %0, %1"
                       : "+r"(ptr)
                       : "r"(0ul));
  if (ptr == 0)
    __builtin_trap();

  uint64_t aa64isar1;
  __asm__ __volatile__("mrs %0, id_aa64isar1_el1" : "=r"(aa64isar1));
  uint64_t apa = (aa64isar1 >> 4) & 0xf;
  uint64_t api = (aa64isar1 >> 8) & 0xf;
  if (fpac_supported(apa) || fpac_supported(api))
    return;

  uint64_t aa64isar2;
  __asm__ __volatile__("mrs %0, id_aa64isar2_el1" : "=r"(aa64isar2));
  uint64_t apa3 = (aa64isar2 >> 12) & 0xf;
  if (fpac_supported(apa3))
    return;

  __builtin_trap();
}

int main(int argc, char **argv) {
  char stack_object1;
  uint64_t ptr1 = (uint64_t)&stack_object1;

  char stack_object2;
  uint64_t ptr2 = (uint64_t)&stack_object2;

  switch (atoi(argv[1])) {
  case 1: {
    // Normal case: test that a pointer authenticated with the same
    // discriminator is equal to the original pointer.
    uint64_t signed_ptr = __emupac_pacda(ptr1, ptr2);
    uint64_t authed_ptr = __emupac_autda(signed_ptr, ptr2);
    if (authed_ptr != ptr1) {
      printf("0x%lx != 0x%lx\n", authed_ptr, ptr1);
      return 1;
    }
    break;
  }
  case 2: {
    // Test that negative addresses (addresses controlled by TTBR1,
    // conventionally kernel addresses) can be signed and authenticated.
    uint64_t unsigned_ptr = -1ULL;
    uint64_t signed_ptr = __emupac_pacda(unsigned_ptr, ptr2);
    uint64_t authed_ptr = __emupac_autda(signed_ptr, ptr2);
    if (authed_ptr != unsigned_ptr) {
      printf("0x%lx != 0x%lx\n", authed_ptr, unsigned_ptr);
      return 1;
    }
    break;
  }
  case 3: {
    crash_if_crash_tests_unsupported();
    // Test that a corrupted signature crashes the program.
    uint64_t signed_ptr = __emupac_pacda(ptr1, ptr2);
    __emupac_autda(signed_ptr + (1ULL << 48), ptr2);
    break;
  }
  case 4: {
    crash_if_crash_tests_unsupported();
    // Test that signing a pointer with signature bits already set produces a pointer
    // that would fail auth.
    uint64_t signed_ptr = __emupac_pacda(ptr1 + (1ULL << 48), ptr2);
    __emupac_autda(signed_ptr, ptr2);
    break;
  }
  }

  return 0;
}