Add a simple test which validates that exit tokens can be written to the GCS of exiting threads, in basic-gcs since this functionality is expected to be used by libcs.
We should add further tests which validate the option being absent. Signed-off-by: Mark Brown <[email protected]> --- tools/testing/selftests/arm64/gcs/basic-gcs.c | 121 ++++++++++++++++++++++++++ 1 file changed, 121 insertions(+) diff --git a/tools/testing/selftests/arm64/gcs/basic-gcs.c b/tools/testing/selftests/arm64/gcs/basic-gcs.c index 54f9c888249d..5515a5425186 100644 --- a/tools/testing/selftests/arm64/gcs/basic-gcs.c +++ b/tools/testing/selftests/arm64/gcs/basic-gcs.c @@ -360,6 +360,126 @@ static bool test_vfork(void) return pass; } +/* We can reuse a shadow stack with an exit token */ +static bool test_exit_token(void) +{ + struct clone_args clone_args; + int ret, status; + static bool pass = true; /* These will be used in the thread */ + static uint64_t expected_cap; + static int elem; + static uint64_t *buf; + + /* Ensure we've got exit tokens enabled here */ + ret = my_syscall5(__NR_prctl, PR_SET_SHADOW_STACK_STATUS, + PR_SHADOW_STACK_ENABLE | PR_SHADOW_STACK_EXIT_TOKEN, + 0, 0, 0); + if (ret != 0) + ksft_exit_fail_msg("Failed to enable exit token: %d\n", ret); + + buf = (void *)my_syscall3(__NR_map_shadow_stack, 0, page_size, + SHADOW_STACK_SET_TOKEN); + if (buf == MAP_FAILED) { + ksft_print_msg("Failed to map %lu byte GCS: %d\n", + page_size, errno); + return false; + } + ksft_print_msg("Mapped GCS at %p-%p\n", buf, + (void *)((uint64_t)buf + page_size)); + + /* We should have a cap token */ + elem = (page_size / sizeof(uint64_t)) - 1; + expected_cap = ((uint64_t)buf + page_size - 8); + expected_cap &= GCS_CAP_ADDR_MASK; + expected_cap |= GCS_CAP_VALID_TOKEN; + if (buf[elem] != expected_cap) { + ksft_print_msg("Cap entry is 0x%llx not 0x%llx\n", + buf[elem], expected_cap); + pass = false; + } + ksft_print_msg("cap token is 0x%llx\n", buf[elem]); + + memset(&clone_args, 0, sizeof(clone_args)); + clone_args.exit_signal = SIGCHLD; + clone_args.flags = CLONE_VM; + clone_args.shstk_token = (uint64_t)&(buf[elem]); + clone_args.stack = (uint64_t)malloc(page_size); + clone_args.stack_size = page_size; + + if (!clone_args.stack) { + ksft_print_msg("Failed to allocate stack\n"); + pass = false; + } + + /* Don't try to clone if we're failing, we might hang */ + if (!pass) + goto out; + + /* There is no wrapper for clone3() in nolibc (or glibc) */ + ret = my_syscall2(__NR_clone3, &clone_args, sizeof(clone_args)); + if (ret == -1) { + ksft_print_msg("clone3() failed: %d\n", errno); + pass = false; + goto out; + } + + if (ret == 0) { + /* In the child, make sure the token is gone */ + if (buf[elem]) { + ksft_print_msg("GCS token was not consumed: %llx\n", + buf[elem]); + pass = false; + } + + /* Make sure we're using the right stack */ + if ((uint64_t)get_gcspr() != (uint64_t)&buf[elem + 1]) { + ksft_print_msg("Child GCSPR_EL0 is %llx not %llx\n", + (uint64_t)get_gcspr(), + (uint64_t)&buf[elem + 1]); + pass = false; + } + + /* We want to exit with *exactly* the same GCS pointer */ + my_syscall1(__NR_exit, 0); + } + + ksft_print_msg("Waiting for child %d\n", ret); + + ret = waitpid(ret, &status, 0); + if (ret == -1) { + ksft_print_msg("Failed to wait for child: %d\n", + errno); + pass = false; + goto out; + } + + if (!WIFEXITED(status)) { + ksft_print_msg("Child exited due to signal %d\n", + WTERMSIG(status)); + pass = false; + } else { + if (WEXITSTATUS(status)) { + ksft_print_msg("Child exited with status %d\n", + WEXITSTATUS(status)); + pass = false; + } + } + + /* The token should have been restored */ + if (buf[elem] == expected_cap) { + ksft_print_msg("Cap entry restored\n"); + } else { + ksft_print_msg("Cap entry is 0x%llx not 0x%llx\n", + buf[elem], expected_cap); + pass = false; + } + +out: + free((void*)clone_args.stack); + munmap(buf, page_size); + return pass; +} + typedef bool (*gcs_test)(void); static struct { @@ -377,6 +497,7 @@ static struct { { "map_guarded_stack", map_guarded_stack }, { "fork", test_fork }, { "vfork", test_vfork }, + { "exit_token", test_exit_token }, }; int main(void) -- 2.47.2
