Date:   Thu, 31 Jan 2019 11:29:25 +0100
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Magnus Karlsson <magnus.karlsson@...el.com>, bjorn.topel@...el.com,
        ast@...nel.org, netdev@...r.kernel.org,
        jakub.kicinski@...ronome.com, bjorn.topel@...il.com,
        qi.z.zhang@...el.com
Cc:     brouer@...hat.com
Subject: Re: [PATCH bpf-next v3 2/3] libbpf: add support for using AF_XDP
 sockets

On 01/29/2019 04:12 PM, Magnus Karlsson wrote:
> This commit adds AF_XDP support to libbpf. The main reason for this is
> to facilitate writing applications that use AF_XDP by offering
> higher-level APIs that hide many of the details of the AF_XDP
> uapi. This is in the same vein as libbpf facilitates XDP adoption by
> offering easy-to-use higher level interfaces of XDP
> functionality. Hopefully this will facilitate adoption of AF_XDP, make
> applications using it simpler and smaller, and finally also make it
> possible for applications to benefit from optimizations in the AF_XDP
> user space access code. Previously, people just copied and pasted the
> code from the sample application into their application, which is not
> desirable.
> 
> The interface is composed of two parts:
> 
> * Low-level access interface to the four rings and the packet
> * High-level control plane interface for creating and setting
>   up umems and af_xdp sockets as well as a simple XDP program.
> 
> Signed-off-by: Magnus Karlsson <magnus.karlsson@...el.com>
[...]
> +
> +static __u32 xsk_prod_nb_free(struct xsk_ring_prod *r, __u32 nb)
> +{
> +	__u32 free_entries = r->cached_cons - r->cached_prod;
> +
> +	if (free_entries >= nb)
> +		return free_entries;
> +
> +	/* Refresh the local tail pointer.
> +	 * cached_cons is r->size bigger than the real consumer pointer so
> +	 * that this addition can be avoided in the more frequently
> +	 * executed code that computs free_entries in the beginning of
> +	 * this function. Without this optimization it whould have been
> +	 * free_entries = r->cached_prod - r->cached_cons + r->size.
> +	 */
> +	r->cached_cons = *r->consumer + r->size;
> +
> +	return r->cached_cons - r->cached_prod;
> +}
> +
> +static __u32 xsk_cons_nb_avail(struct xsk_ring_cons *r, __u32 nb)
> +{
> +	__u32 entries = r->cached_prod - r->cached_cons;
> +
> +	if (entries == 0) {
> +		r->cached_prod = *r->producer;
> +		entries = r->cached_prod - r->cached_cons;
> +	}
> +
> +	return (entries > nb) ? nb : entries;
> +}
> +
> +size_t xsk_ring_prod__reserve(struct xsk_ring_prod *prod, size_t nb, __u32 *idx)
> +{
> +	if (unlikely(xsk_prod_nb_free(prod, nb) < nb))
> +		return 0;
> +
> +	*idx = prod->cached_prod;
> +	prod->cached_prod += nb;
> +
> +	return nb;
> +}
> +
> +void xsk_ring_prod__submit(struct xsk_ring_prod *prod, size_t nb)
> +{
> +	/* Make sure everything has been written to the ring before signalling
> +	 * this to the kernel.
> +	 */
> +	smp_wmb();
> +
> +	*prod->producer += nb;
> +}
> +
> +size_t xsk_ring_cons__peek(struct xsk_ring_cons *cons, size_t nb, __u32 *idx)
> +{
> +	size_t entries = xsk_cons_nb_avail(cons, nb);
> +
> +	if (likely(entries > 0)) {
> +		/* Make sure we do not speculatively read the data before
> +		 * we have received the packet buffers from the ring.
> +		 */
> +		smp_rmb();
> +
> +		*idx = cons->cached_cons;
> +		cons->cached_cons += entries;
> +	}
> +
> +	return entries;
> +}
> +
> +void xsk_ring_cons__release(struct xsk_ring_cons *cons, size_t nb)
> +{
> +	*cons->consumer += nb;
> +}
> +
> +void *xsk_umem__get_data_raw(void *umem_area, __u64 addr)
> +{
> +	return &((char *)umem_area)[addr];
> +}
> +
> +void *xsk_umem__get_data(struct xsk_umem *umem, __u64 addr)
> +{
> +	return &((char *)(umem->umem_area))[addr];
> +}

Shouldn't some of the above helpers for critical path be exposed as static
inline functions instead?

[...]
> +static int xsk_parse_nl(void *cookie, void *msg, struct nlattr **tb)
> +{
> +	struct nlattr *tb_parsed[IFLA_XDP_MAX + 1];
> +	struct xsk_nl_info *nl_info = cookie;
> +	unsigned char mode;
> +	int err;
> +
> +	(void)msg;

Unused?

> +	nl_info->xdp_prog_attached = false;
> +	if (!tb[IFLA_XDP])
> +		return 0;
> +
> +	err = libbpf_nla_parse_nested(tb_parsed, IFLA_XDP_MAX, tb[IFLA_XDP],
> +				      NULL);
> +	if (err)
> +		return err;
> +
> +	if (!tb_parsed[IFLA_XDP_ATTACHED] || !tb_parsed[IFLA_XDP_FD])
> +		return 0;
> +
> +	mode = libbpf_nla_getattr_u8(tb_parsed[IFLA_XDP_ATTACHED]);
> +	if (mode == XDP_ATTACHED_NONE)
> +		return 0;

Probably good to memset and/or init the passed struct xsk_nl_info (e.g.
fd to -1 etc) such that if some user did not we won't end up with garbage
values on return 0.

> +	nl_info->xdp_prog_attached = true;
> +	nl_info->fd = libbpf_nla_getattr_u32(tb_parsed[IFLA_XDP_FD]);
> +	return 0;
> +}
> +
> +static bool xsk_xdp_prog_attached(struct xsk_socket *xsk)
> +{
> +	struct xsk_nl_info nl_info;
> +	unsigned int nl_pid;
> +	char err_buf[256];
> +	int sock, err;
> +
> +	sock = libbpf_netlink_open(&nl_pid);
> +	if (sock < 0)
> +		return false;
> +
> +	nl_info.xdp_prog_attached = false;
> +	nl_info.fd = 0;
> +
> +	err = libbpf_nl_get_link(sock, nl_pid, xsk_parse_nl, &nl_info);
> +	if (err) {
> +		libbpf_strerror(err, err_buf, sizeof(err_buf));
> +		pr_warning("Error:\n%s\n", err_buf);
> +		return false;
> +	}
> +
> +	xsk->prog_fd = nl_info.fd;
> +	return nl_info.xdp_prog_attached;

Don't we leak sock here and in error above?

> +}
> +
> +static int xsk_load_xdp_prog(struct xsk_socket *xsk)
> +{
> +	char bpf_log_buf[BPF_LOG_BUF_SIZE];
> +	int err, prog_fd;
> +
> +	/* This is the C-program:
> +	 * SEC("xdp_sock") int xdp_sock_prog(struct xdp_md *ctx)
> +	 * {
> +	 *     int *qidconf, index = ctx->rx_queue_index;
> +	 *
> +	 *     // A set entry here means that the correspnding queue_id
> +	 *     // has an active AF_XDP socket bound to it.
> +	 *     qidconf = bpf_map_lookup_elem(&qidconf_map, &index);
> +	 *     if (!qidconf)
> +	 *         return XDP_ABORTED;
> +	 *
> +	 *     if (*qidconf)
> +	 *         return bpf_redirect_map(&xsks_map, index, 0);
> +	 *
> +	 *     return XDP_PASS;
> +	 * }
> +	 */
> +	struct bpf_insn prog[] = {
> +		/* r1 = *(u32 *)(r1 + 16) */
> +		BPF_LDX_MEM(BPF_W, BPF_REG_1, BPF_REG_1, 16),
> +		/* *(u32 *)(r10 - 4) = r1 */
> +		BPF_STX_MEM(BPF_W, BPF_REG_10, BPF_REG_1, -4),
> +		BPF_MOV64_REG(BPF_REG_2, BPF_REG_10),
> +		BPF_ALU64_IMM(BPF_ADD, BPF_REG_2, -4),
> +		BPF_LD_MAP_FD(BPF_REG_1, xsk->qidconf_map_fd),
> +		BPF_EMIT_CALL(BPF_FUNC_map_lookup_elem),
> +		BPF_MOV64_REG(BPF_REG_1, BPF_REG_0),
> +		BPF_MOV32_IMM(BPF_REG_0, 0),
> +		/* if r1 == 0 goto +8 */
> +		BPF_JMP_IMM(BPF_JEQ, BPF_REG_1, 0, 8),
> +		BPF_MOV32_IMM(BPF_REG_0, 2),
> +		/* r1 = *(u32 *)(r1 + 0) */
> +		BPF_LDX_MEM(BPF_W, BPF_REG_1, BPF_REG_1, 0),
> +		/* if r1 == 0 goto +5 */
> +		BPF_JMP_IMM(BPF_JEQ, BPF_REG_1, 0, 5),
> +		/* r2 = *(u32 *)(r10 - 4) */
> +		BPF_LD_MAP_FD(BPF_REG_1, xsk->xsks_map_fd),
> +		BPF_LDX_MEM(BPF_W, BPF_REG_2, BPF_REG_10, -4),
> +		BPF_MOV32_IMM(BPF_REG_3, 0),
> +		BPF_EMIT_CALL(BPF_FUNC_redirect_map),
> +		/* The jumps are to this instruction */
> +		BPF_EXIT_INSN(),
> +	};
> +	size_t insns_cnt = sizeof(prog) / sizeof(struct bpf_insn);
> +
> +	prog_fd = bpf_load_program(BPF_PROG_TYPE_XDP, prog, insns_cnt,
> +				   "LGPL-2.1 or BSD-2-Clause", 0, bpf_log_buf,
> +				   BPF_LOG_BUF_SIZE);
> +	if (prog_fd < 0) {
> +		pr_warning("BPF log buffer:\n%s", bpf_log_buf);
> +		return prog_fd;
> +	}
> +
> +	err = bpf_set_link_xdp_fd(xsk->ifindex, prog_fd, xsk->config.xdp_flags);
> +	if (err)
> +		return err;

Leaks prog_fd on error.

> +	xsk->prog_fd = prog_fd;
> +	return 0;
> +}
> +
> +static int xsk_create_bpf_maps(struct xsk_socket *xsk)
> +{
> +	int fd;
> +
> +	fd = bpf_create_map_name(BPF_MAP_TYPE_ARRAY, "qidconf_map",
> +				 sizeof(int), sizeof(int), MAX_QUEUES, 0);
> +	if (fd < 0)
> +		return fd;
> +	xsk->qidconf_map_fd = fd;
> +
> +	fd = bpf_create_map_name(BPF_MAP_TYPE_XSKMAP, "xsks_map",
> +				 sizeof(int), sizeof(int), MAX_QUEUES, 0);
> +	if (fd < 0)
> +		return fd;

Leaks first map fd on error.

> +	xsk->xsks_map_fd = fd;
> +
> +	return 0;
> +}
> +
> +static int xsk_update_bpf_maps(struct xsk_socket *xsk, int qidconf_value,
> +			       int xsks_value)
> +{
> +	bool qidconf_map_updated = false, xsks_map_updated = false;
> +	struct bpf_prog_info prog_info = {};
> +	__u32 prog_len = sizeof(prog_info);
> +	struct bpf_map_info map_info;
> +	__u32 map_len = sizeof(map_info);
> +	__u32 *map_ids;
> +	int reset_value = 0;
> +	__u32 num_maps;
> +	unsigned int i;
> +	int err;
> +
> +	err = bpf_obj_get_info_by_fd(xsk->prog_fd, &prog_info, &prog_len);
> +	if (err)
> +		return err;
> +
> +	num_maps = prog_info.nr_map_ids;
> +
> +	map_ids = malloc(prog_info.nr_map_ids * sizeof(*map_ids));

calloc()?

> +	if (!map_ids)
> +		return -ENOMEM;
> +
> +	memset(&prog_info, 0, prog_len);
> +	prog_info.nr_map_ids = num_maps;
> +	prog_info.map_ids = (__u64)(unsigned long)map_ids;
> +
> +	err = bpf_obj_get_info_by_fd(xsk->prog_fd, &prog_info, &prog_len);
> +	if (err)
> +		return err;

Leaks map_ids on error.

> +
> +	for (i = 0; i < prog_info.nr_map_ids; i++) {
> +		int fd;
> +
> +		fd = bpf_map_get_fd_by_id(map_ids[i]);
> +		if (fd < 0) {
> +			err = -errno;
> +			goto out;
> +		}
> +
> +		err = bpf_obj_get_info_by_fd(fd, &map_info, &map_len);
> +		if (err)
> +			goto out;

close(fd) on error, also the case for below, please double check everything
so that no fd leaks by accident into the app.

> +
> +		if (!strcmp(map_info.name, "qidconf_map")) {
> +			err = bpf_map_update_elem(fd, &xsk->queue_id,
> +						  &qidconf_value, 0);
> +			if (err)
> +				goto out;
> +			qidconf_map_updated = true;
> +			xsk->qidconf_map_fd = fd;
> +		} else if (!strcmp(map_info.name, "xsks_map")) {
> +			err = bpf_map_update_elem(fd, &xsk->queue_id,
> +						  &xsks_value, 0);
> +			if (err)
> +				goto out;> +			xsks_map_updated = true;
> +			xsk->xsks_map_fd = fd;
> +		}
> +
> +		if (qidconf_map_updated && xsks_map_updated)
> +			break;
> +	}
> +
> +	if (!(qidconf_map_updated && xsks_map_updated)) {
> +		err = -ENOENT;
> +		goto out;
> +	}
> +
> +	return 0;
> +
> +out:
> +	if (qidconf_map_updated)
> +		(void)bpf_map_update_elem(xsk->qidconf_map_fd, &xsk->queue_id,
> +					  &reset_value, 0);
> +	if (xsks_map_updated)
> +		(void)bpf_map_update_elem(xsk->xsks_map_fd, &xsk->queue_id,
> +					  &reset_value, 0);
> +	return err;
> +}
> +
> +static int xsk_setup_xdp_prog(struct xsk_socket *xsk)
> +{
> +	bool prog_loaded = false;
> +	int err;
> +
> +	if (!xsk_xdp_prog_attached(xsk)) {
> +		err = xsk_create_bpf_maps(xsk);
> +		if (err)
> +			goto out_load;
> +
> +		err = xsk_load_xdp_prog(xsk);
> +		if (err)
> +			return err;

Needs to undo created maps on error.

> +		prog_loaded = true;
> +	}
> +
> +	err = xsk_update_bpf_maps(xsk, true, xsk->fd);
> +	if (err)
> +		goto out_load;
> +
> +	return 0;
> +
> +out_load:
> +	if (prog_loaded)
> +		close(xsk->prog_fd);

Ditto

> +	return err;
> +}
> +
> +int xsk_socket__create(struct xsk_socket **xsk_ptr, const char *ifname,
> +		       __u32 queue_id, struct xsk_umem *umem,
> +		       struct xsk_ring_cons *rx, struct xsk_ring_prod *tx,
> +		       const struct xsk_socket_config *usr_config)
> +{
> +	struct sockaddr_xdp sxdp = {};
> +	struct xdp_mmap_offsets off;
> +	struct xsk_socket *xsk;
> +	socklen_t optlen;
> +	void *map;

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