genode/repos/base-linux/src/lib/base/ipc.cc

/*
 * \brief  Socket-based IPC implementation for Linux
 * \author Norman Feske
 * \author Christian Helmuth
 * \date   2011-10-11
 */

/*
 * Copyright (C) 2011-2017 Genode Labs GmbH
 *
 * This file is part of the Genode OS framework, which is distributed
 * under the terms of the GNU Affero General Public License version 3.
 */

/* Genode includes */
#include <base/ipc.h>
#include <base/thread.h>
#include <base/blocking.h>
#include <base/env.h>
#include <linux_native_cpu/linux_native_cpu.h>

/* base-internal includes */
#include <base/internal/socket_descriptor_registry.h>
#include <base/internal/native_thread.h>
#include <base/internal/ipc_server.h>
#include <base/internal/server_socket_pair.h>
#include <base/internal/capability_space_tpl.h>

/* Linux includes */
#include <linux_syscalls.h>

using namespace Genode;


namespace {

	struct Pid
	{
		int value;

		Pid() : value(lx_getpid()) { }

		void print(Output &out) const { Genode::print(out, "[", value, "]"); }
	};
}


/*
 * The request message layout is:
 *
 *   long  local_name;
 *   ...call arguments, starting with the opcode...
 *
 * Response messages look like this:
 *
 *   long  exception code
 *   ...call results...
 *
 * First data word of message, used to transfer the local name of the invoked
 * object (when a client calls a server) or the exception code (when the server
 * replies). This data word is never fetched from memory but transferred via
 * the first short-IPC register. The 'protocol_word' is needed as a spacer
 * between the header fields define above and the regular message payload..
 */
struct Protocol_header
{
	/* badge of invoked object (on call) / exception code (on reply) */
	unsigned long protocol_word;

	Genode::size_t num_caps;

	/* badges of the transferred capability arguments */
	unsigned long badges[Msgbuf_base::MAX_CAPS_PER_MSG];

	enum { INVALID_BADGE = ~1UL };

	void *msg_start() { return &protocol_word; }
};


/*
 * The INVALID_BADGE must be different from the representation of an
 * invalid RPC object key because this key value is used by manually
 * created NON-RPC-object capabilities (client_sd, server_sd, dataspace fd).
 */
static_assert((int)Protocol_header::INVALID_BADGE != (int)Rpc_obj_key::INVALID,
              "ambigious INVALID_BADGE");


/******************************
 ** File-descriptor registry **
 ******************************/

Genode::Ep_socket_descriptor_registry &Genode::ep_sd_registry()
{
	static Genode::Ep_socket_descriptor_registry registry;
	return registry;
}


/********************************************
 ** Communication over Unix-domain sockets **
 ********************************************/

enum {
	LX_EINTR        = 4,
	LX_ECONNREFUSED = 111
};


/**
 * Utility: Return thread ID to which the given socket is directed to
 *
 * \return -1  if the socket is pointing to a valid entrypoint
 */
static int lookup_tid_by_client_socket(int sd)
{
	/*
	 * Synchronize calls so that the large 'sockaddr_un' can be allocated
	 * in the BSS rather than the stack.
	 */
	static Lock lock;
	Lock::Guard guard(lock);

	static sockaddr_un name;
	socklen_t name_len = sizeof(name);
	int ret = lx_getpeername(sd, (sockaddr *)&name, &name_len);
	if (ret < 0)
		return -1;

	struct Prefix_len
	{
		typedef Genode::size_t size_t;

		size_t const len;

		static int _init_len(char const *s)
		{
			char  const * const pattern     = "/ep-";
			static size_t const pattern_len = Genode::strlen(pattern);

			for (size_t i = 0; Genode::strlen(s + i) >= pattern_len; i++)
				if (Genode::strcmp(s + i, pattern, pattern_len) == 0)
					return i + pattern_len;

			struct Unexpected_rpath_prefix { };
			throw  Unexpected_rpath_prefix();
		}

		Prefix_len(char const *s) : len(_init_len(s)) { }
	};

	/*
	 * The name of the Unix-domain socket has the form <rpath>-<uid>/ep-<tid>.
	 * We are only interested in the <tid> part. Hence, we determine the length
	 * of the <rpath>-<uid>/ep- portion only once and keep it in a static
	 * variable.
	 */
	static Prefix_len prefix_len(name.sun_path);

	unsigned tid = 0;
	if (Genode::ascii_to(name.sun_path + prefix_len.len, tid) == 0) {
		raw("Error: could not parse tid number");
		return -1;
	}
	return tid;
}


namespace {

	/**
	 * Message object encapsulating data for sendmsg/recvmsg
	 */
	struct Message
	{
		public:

			enum { MAX_SDS_PER_MSG = Genode::Msgbuf_base::MAX_CAPS_PER_MSG + 1 };

		private:

			typedef Genode::size_t size_t;

			msghdr      _msg   { };
			sockaddr_un _addr  { };
			iovec       _iovec { };
			char        _cmsg_buf[CMSG_SPACE(MAX_SDS_PER_MSG*sizeof(int))];

			unsigned _num_sds;

		public:

			Message(void *buffer, size_t buffer_len) : _num_sds(0)
			{
				Genode::memset(&_msg, 0, sizeof(_msg));

				/* initialize control message */
				struct cmsghdr *cmsg;

				_msg.msg_control     = _cmsg_buf;
				_msg.msg_controllen  = sizeof(_cmsg_buf);  /* buffer space available */
				_msg.msg_flags      |= MSG_CMSG_CLOEXEC;
				cmsg                 = CMSG_FIRSTHDR(&_msg);
				cmsg->cmsg_len       = CMSG_LEN(0);
				cmsg->cmsg_level     = SOL_SOCKET;
				cmsg->cmsg_type      = SCM_RIGHTS;
				_msg.msg_controllen  = cmsg->cmsg_len;     /* actual cmsg length */

				/* initialize iovec */
				_msg.msg_iov    = &_iovec;
				_msg.msg_iovlen = 1;

				_iovec.iov_base = buffer;
				_iovec.iov_len  = buffer_len;
			}

			msghdr * msg() { return &_msg; }

			void marshal_socket(int sd)
			{
				*((int *)CMSG_DATA((cmsghdr *)_cmsg_buf) + _num_sds) = sd;

				struct cmsghdr *cmsg = CMSG_FIRSTHDR(&_msg);
				if (cmsg) {
					_num_sds++;
					cmsg->cmsg_len       = CMSG_LEN(_num_sds*sizeof(int));
					_msg.msg_controllen  = cmsg->cmsg_len;     /* actual cmsg length */
				}
			}

			void accept_sockets(int num_sds)
			{
				struct cmsghdr *cmsg = CMSG_FIRSTHDR(&_msg);
				cmsg->cmsg_len       = CMSG_LEN(num_sds*sizeof(int));
				_msg.msg_controllen  = cmsg->cmsg_len;     /* actual cmsg length */
			}

			int socket_at_index(int index) const
			{
				return *((int *)CMSG_DATA((cmsghdr *)_cmsg_buf) + index);
			}

			unsigned num_sockets() const
			{
				struct cmsghdr *cmsg = CMSG_FIRSTHDR(&_msg);

				if (!cmsg)
					return 0;

				return (cmsg->cmsg_len - CMSG_ALIGN(sizeof(cmsghdr)))/sizeof(int);
			}
	};

} /* unnamed namespace */


static void insert_sds_into_message(Message &msg,
                                    Protocol_header &header,
                                    Genode::Msgbuf_base &snd_msgbuf)
{
	for (unsigned i = 0; i < snd_msgbuf.used_caps(); i++) {

		Native_capability const &cap = snd_msgbuf.cap(i);

		if (cap.valid()) {
			Capability_space::Ipc_cap_data cap_data =
				Capability_space::ipc_cap_data(cap);

			msg.marshal_socket(cap_data.dst.socket);
			header.badges[i] = cap_data.rpc_obj_key.value();
		} else {
			header.badges[i] = Protocol_header::INVALID_BADGE;
		}

	}
	header.num_caps = snd_msgbuf.used_caps();
}


/**
 * Utility: Extract socket desriptors from SCM message into 'Genode::Msgbuf'
 */
static void extract_sds_from_message(unsigned start_index,
                                     Message const &msg,
                                     Protocol_header const &header,
                                     Genode::Msgbuf_base &buf)
{
	unsigned sd_cnt = 0;
	for (unsigned i = 0; i < min(header.num_caps, (size_t)Msgbuf_base::MAX_CAPS_PER_MSG); i++) {

		unsigned long const badge = header.badges[i];

		/* an invalid capabity was transferred */
		if (badge == Protocol_header::INVALID_BADGE) {
			buf.insert(Native_capability());
			continue;
		}

		int const sd = msg.socket_at_index(start_index + sd_cnt++);
		int const id = lookup_tid_by_client_socket(sd);

		int const associated_sd = Genode::ep_sd_registry().try_associate(sd, id);

		Native_capability arg_cap = Capability_space::lookup(Rpc_obj_key(badge));

		if (arg_cap.valid()) {

			/*
			 * Discard the received selector and keep using the already
			 * present one.
			 */

			buf.insert(arg_cap);
		} else {
			buf.insert(Capability_space::import(Rpc_destination(associated_sd),
			                                    Rpc_obj_key(badge)));
		}

		if ((associated_sd >= 0) && (associated_sd != sd)) {

			/*
			 * The association already existed under a different name, use
			 * already associated socket descriptor and and drop 'sd'.
			 */
			lx_close(sd);
		}
	}
}


/**
 * Send reply to client
 */
static inline void lx_reply(int reply_socket, Rpc_exception_code exception_code,
                            Genode::Msgbuf_base &snd_msgbuf)
{

	Protocol_header &header = snd_msgbuf.header<Protocol_header>();

	header.protocol_word = exception_code.value;

	Message msg(header.msg_start(), sizeof(Protocol_header) + snd_msgbuf.data_size());

	/* marshall capabilities to be transferred to the client */
	insert_sds_into_message(msg, header, snd_msgbuf);

	int const ret = lx_sendmsg(reply_socket, msg.msg(), 0);

	/* ignore reply send error caused by disappearing client */
	if (ret >= 0 || ret == -LX_ECONNREFUSED) {
		lx_close(reply_socket);
		return;
	}

	if (ret < 0)
		raw("[", lx_gettid, "] lx_sendmsg failed with ", ret, " "
		    "in lx_reply() reply_socket=", reply_socket);
}


/****************
 ** IPC client **
 ****************/

Rpc_exception_code Genode::ipc_call(Native_capability dst,
                                    Msgbuf_base &snd_msgbuf, Msgbuf_base &rcv_msgbuf,
                                    size_t)
{
	Protocol_header &snd_header = snd_msgbuf.header<Protocol_header>();
	snd_header.protocol_word = dst.local_name();

	Message snd_msg(snd_header.msg_start(),
	                sizeof(Protocol_header) + snd_msgbuf.data_size());

	/*
	 * Create reply channel
	 *
	 * The reply channel will be closed when leaving the scope of 'lx_call'.
	 */
	struct Reply_channel
	{
		enum { LOCAL_SOCKET = 0, REMOTE_SOCKET = 1 };
		int sd[2];

		Reply_channel()
		{
			sd[LOCAL_SOCKET] = -1; sd[REMOTE_SOCKET] = -1;

			int ret = lx_socketpair(AF_UNIX, SOCK_DGRAM | SOCK_CLOEXEC, 0, sd);
			if (ret < 0) {
				raw("[", lx_gettid(), "] lx_socketpair failed with ", ret);
				throw Genode::Ipc_error();
			}
		}

		~Reply_channel()
		{
			if (sd[LOCAL_SOCKET]  != -1) lx_close(sd[LOCAL_SOCKET]);
			if (sd[REMOTE_SOCKET] != -1) lx_close(sd[REMOTE_SOCKET]);
		}

		int local_socket()  const { return sd[LOCAL_SOCKET];  }
		int remote_socket() const { return sd[REMOTE_SOCKET]; }

	} reply_channel;

	/* assemble message */

	/* marshal reply capability */
	snd_msg.marshal_socket(reply_channel.remote_socket());

	/* marshal capabilities contained in 'snd_msgbuf' */
	insert_sds_into_message(snd_msg, snd_header, snd_msgbuf);

	int const dst_socket = Capability_space::ipc_cap_data(dst).dst.socket;

	int const send_ret = lx_sendmsg(dst_socket, snd_msg.msg(), 0);
	if (send_ret < 0) {
		raw(Pid(), " lx_sendmsg to sd ", dst_socket,
		    " failed with ", send_ret, " in lx_call()");
		for (;;);
		throw Genode::Ipc_error();
	}

	/* receive reply */
	Protocol_header &rcv_header = rcv_msgbuf.header<Protocol_header>();
	rcv_header.protocol_word = 0;

	Message rcv_msg(rcv_header.msg_start(),
	                sizeof(Protocol_header) + rcv_msgbuf.capacity());
	rcv_msg.accept_sockets(Message::MAX_SDS_PER_MSG);

	rcv_msgbuf.reset();
	int const recv_ret = lx_recvmsg(reply_channel.local_socket(), rcv_msg.msg(), 0);

	/* system call got interrupted by a signal */
	if (recv_ret == -LX_EINTR)
		throw Genode::Blocking_canceled();

	if (recv_ret < 0) {
		raw("[", lx_getpid(), "] lx_recvmsg failed with ", recv_ret, " in lx_call()");
		throw Genode::Ipc_error();
	}

	extract_sds_from_message(0, rcv_msg, rcv_header, rcv_msgbuf);

	return Rpc_exception_code(rcv_header.protocol_word);
}


/****************
 ** IPC server **
 ****************/

void Genode::ipc_reply(Native_capability caller, Rpc_exception_code exc,
                       Msgbuf_base &snd_msg)
{
	int const reply_socket = Capability_space::ipc_cap_data(caller).dst.socket;

	try { lx_reply(reply_socket, exc, snd_msg); } catch (Ipc_error) { }
}


Genode::Rpc_request Genode::ipc_reply_wait(Reply_capability const &last_caller,
                                           Rpc_exception_code      exc,
                                           Msgbuf_base            &reply_msg,
                                           Msgbuf_base            &request_msg)
{
	/* when first called, there was no request yet */
	if (last_caller.valid() && exc.value != Rpc_exception_code::INVALID_OBJECT)
		lx_reply(Capability_space::ipc_cap_data(last_caller).dst.socket, exc, reply_msg);

	/*
	 * Block infinitely if called from the main thread. This may happen if the
	 * main thread calls 'sleep_forever()'.
	 */
	if (!Thread::myself()) {
		struct timespec ts = { 1000, 0 };
		for (;;) lx_nanosleep(&ts, 0);
	}

	for (;;) {

		Protocol_header &header = request_msg.header<Protocol_header>();
		Message msg(header.msg_start(), sizeof(Protocol_header) + request_msg.capacity());

		msg.accept_sockets(Message::MAX_SDS_PER_MSG);

		Native_thread &native_thread = Thread::myself()->native_thread();

		request_msg.reset();
		int const ret = lx_recvmsg(native_thread.socket_pair.server_sd, msg.msg(), 0);

		/* system call got interrupted by a signal */
		if (ret == -LX_EINTR)
			continue;

		if (ret < 0) {
			raw("lx_recvmsg failed with ", ret, " in ipc_reply_wait, sd=",
			    native_thread.socket_pair.server_sd);
			continue;
		}

		int           const reply_socket = msg.socket_at_index(0);
		unsigned long const badge        = header.protocol_word;

		/* start at offset 1 to skip the reply channel */
		extract_sds_from_message(1, msg, header, request_msg);

		return Rpc_request(Capability_space::import(Rpc_destination(reply_socket),
		                                            Rpc_obj_key()), badge);
	}
}


Ipc_server::Ipc_server()
:
	Native_capability(Capability_space::import(Rpc_destination(), Rpc_obj_key()))
{
	/*
	 * If 'thread' is 0, the constructor was called by the main thread. By
	 * definition, main is never an RPC entrypoint. However, the main thread
	 * may call 'sleep_forever()', which instantiates 'Ipc_server'.
	 */
	if (!Thread::myself())
		return;

	Native_thread &native_thread = Thread::myself()->native_thread();

	if (native_thread.is_ipc_server) {
		Genode::raw("[", lx_gettid(), "] "
		            " unexpected multiple instantiation of Ipc_server by one thread");
		struct Ipc_server_multiple_instance { };
		throw Ipc_server_multiple_instance();
	}

	Socket_pair const socket_pair = server_socket_pair();

	native_thread.socket_pair    = socket_pair;
	native_thread.is_ipc_server = true;

	/* override capability initialization */
	*static_cast<Native_capability *>(this) =
		Capability_space::import(Rpc_destination(socket_pair.client_sd),
		                         Rpc_obj_key());
}


Ipc_server::~Ipc_server()
{
	if (!Thread::myself())
		return;

	/*
	 * Reset thread role to non-server such that we can enter 'sleep_forever'
	 * without getting a warning.
	 */
	Native_thread &native_thread = Thread::myself()->native_thread();

	Genode::ep_sd_registry().disassociate(native_thread.socket_pair.client_sd);
	native_thread.is_ipc_server = false;

	destroy_server_socket_pair(native_thread.socket_pair);
	native_thread.socket_pair = Socket_pair();
}