discovering native audit arch

[Kees Cook <keescook@xxxxxxxxxxxx>]

Hi,

Is there a better way than this to find the native architecture value
needed for seccomp filters? Right now everyone basically hard-codes it
with other compile-time checks...

static unsigned int get_syscall_arch(void)
{
	struct ptrace_syscall_info info = { };
	siginfo_t siginfo = { };
	unsigned int arch = -1;
	pid_t pid = fork();

	if (pid < 0)
		return -1;
	if (pid == 0) {
		if (ptrace(PTRACE_TRACEME, 0, 0, 0) != 0) {
			perror("PTRACE_TRACEME");
			_exit(1);
		}
		if (raise(SIGSTOP) != 0) {
			perror("raise");
			_exit(1);
		}
		_exit(0);
	}
	if (ptrace(PTRACE_ATTACH, pid, 0, 0) != 0)
		goto reap;
	if (waitid(P_PID, pid, &siginfo, WEXITED | WSTOPPED | WCONTINUED) != 0)
		goto reap;
	if (siginfo.si_code != CLD_STOPPED &&
	    siginfo.si_code != CLD_TRAPPED)
		goto reap;
	if (ptrace(PTRACE_GET_SYSCALL_INFO, pid, sizeof(info), &info)
	    < offsetof(typeof(info), arch) + sizeof(info.arch))
		goto reap;
	arch = info.arch;
	ptrace(PTRACE_DETACH, pid, 0, 0);
reap:
	kill(pid, SIGKILL);
	if (waitpid(pid, NULL, 0) != pid)
		perror("waitpid");
	return arch;
}


-- 
Kees Cook