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Date:   Fri, 26 Apr 2019 10:52:20 -0700
From:   Stanislav Fomichev <sdf@...ichev.me>
To:     Martin KaFai Lau <kafai@...com>
Cc:     bpf@...r.kernel.org, netdev@...r.kernel.org,
        Alexei Starovoitov <ast@...com>,
        Andrii Nakryiko <andriin@...com>,
        Daniel Borkmann <daniel@...earbox.net>,
        John Fastabend <john.fastabend@...il.com>, kernel-team@...com,
        Yonghong Song <yhs@...com>
Subject: Re: [PATCH v3 bpf-next 1/6] bpf: Introduce bpf sk local storage

On 04/26, Martin KaFai Lau wrote:
> After allowing a bpf prog to
> - directly read the skb->sk ptr
> - get the fullsock bpf_sock by "bpf_sk_fullsock()"
> - get the bpf_tcp_sock by "bpf_tcp_sock()"
> - get the listener sock by "bpf_get_listener_sock()"
> - avoid duplicating the fields of "(bpf_)sock" and "(bpf_)tcp_sock"
>   into different bpf running context.
> 
> this patch is another effort to make bpf's network programming
> more intuitive to do (together with memory and performance benefit).
> 
> When bpf prog needs to store data for a sk, the current practice is to
> define a map with the usual 4-tuples (src/dst ip/port) as the key.
> If multiple bpf progs require to store different sk data, multiple maps
> have to be defined.  Hence, wasting memory to store the duplicated
> keys (i.e. 4 tuples here) in each of the bpf map.
> [ The smallest key could be the sk pointer itself which requires
>   some enhancement in the verifier and it is a separate topic. ]
> 
> Also, the bpf prog needs to clean up the elem when sk is freed.
> Otherwise, the bpf map will become full and un-usable quickly.
> The sk-free tracking currently could be done during sk state
> transition (e.g. BPF_SOCK_OPS_STATE_CB).
> 
> The size of the map needs to be predefined which then usually ended-up
> with an over-provisioned map in production.  Even the map was re-sizable,
> while the sk naturally come and go away already, this potential re-size
> operation is arguably redundant if the data can be directly connected
> to the sk itself instead of proxy-ing through a bpf map.
> 
> This patch introduces sk->sk_bpf_storage to provide local storage space
> at sk for bpf prog to use.  The space will be allocated when the first bpf
> prog has created data for this particular sk.
> 
> The design optimizes the bpf prog's lookup (and then optionally followed by
> an inline update).  bpf_spin_lock should be used if the inline update needs
> to be protected.
> 
> BPF_MAP_TYPE_SK_STORAGE:
> -----------------------
> To define a bpf "sk-local-storage", a BPF_MAP_TYPE_SK_STORAGE map (new in
> this patch) needs to be created.  Multiple BPF_MAP_TYPE_SK_STORAGE maps can
> be created to fit different bpf progs' needs.  The map enforces
> BTF to allow printing the sk-local-storage during a system-wise
> sk dump (e.g. "ss -ta") in the future.
> 
> The purpose of a BPF_MAP_TYPE_SK_STORAGE map is not for lookup/update/delete
> a "sk-local-storage" data from a particular sk.
> Think of the map as a meta-data (or "type") of a "sk-local-storage".  This
> particular "type" of "sk-local-storage" data can then be stored in any sk.
> 
> The main purposes of this map are mostly:
> 1. Define the size of a "sk-local-storage" type.
> 2. Provide a similar syscall userspace API as the map (e.g. lookup/update,
>    map-id, map-btf...etc.)
> 3. Keep track of all sk's storages of this "type" and clean them up
>    when the map is freed.
> 
> sk->sk_bpf_storage:
> ------------------
> The main lookup/update/delete is done on sk->sk_bpf_storage (which
> is a "struct bpf_sk_storage").  When doing a lookup,
> the "map" pointer is now used as the "key" to search on the
> sk_storage->list.  The "map" pointer is actually serving
> as the "type" of the "sk-local-storage" that is being
> requested.
> 
> To allow very fast lookup, it should be as fast as looking up an
> array at a stable-offset.  At the same time, it is not ideal to
> set a hard limit on the number of sk-local-storage "type" that the
> system can have.  Hence, this patch takes a cache approach.
> The last search result from sk_storage->list is cached in
> sk_storage->cache[] which is a stable sized array.  Each
> "sk-local-storage" type has a stable offset to the cache[] array.
> In the future, a map's flag could be introduced to do cache
> opt-out/enforcement if it became necessary.
> 
> All data will be removed from sk->sk_bpf_storage during
> sk destruction.
> 
> bpf_sk_storage_get() and bpf_sk_storage_delete():
> ------------------------------------------------
> Instead of using bpf_map_(lookup|update|delete)_elem(),
> the bpf prog needs to use the new helper bpf_sk_storage_get() and
> bpf_sk_storage_delete().  The verifier can then enforce the
> ARG_PTR_TO_SOCKET argument.  The bpf_sk_storage_get() also allows to
> "create" new elem if one does not exist in the sk.  It is done by
> the new BPF_SK_STORAGE_GET_F_CREATE flag.  An optional value can also be
> provided as the initial value during BPF_SK_STORAGE_GET_F_CREATE.
> The BPF_MAP_TYPE_SK_STORAGE also supports bpf_spin_lock.  Together,
> it has eliminated the potential use cases for an equivalent
> bpf_map_update_elem() API (for bpf_prog) in this patch.
> 
> Misc notes:
> ----------
> 1. map_get_next_key is not supported.  From the userspace syscall
>    perspective,  the map has the socket fd as the key while the map
>    can be shared by pinned-file or map-id.
> 
>    Since btf is enforced, the existing "ss" could be enhanced to pretty
>    print the local-storage.
> 
>    Supporting a kernel defined btf with 4 tuples as the return key could
>    be explored later also.
> 
> 2. The sk->sk_lock cannot be acquired.  Atomic operations is used instead.
>    e.g. cmpxchg is done on the sk->sk_bpf_storage ptr.
>    Please refer to the source code comments for the details in
>    synchronization cases and considerations.
> 
> 3. The mem is charged to the sk->sk_omem_alloc as the sk filter does.
> 
> Benchmark:
> ---------
> Here is the benchmark data collected by turning on
> the "kernel.bpf_stats_enabled" sysctl.
> Two bpf progs are tested:
> 
> One bpf prog with the usual bpf hashmap (max_entries = 8192) with the
> sk ptr as the key. (verifier is modified to support sk ptr as the key
> That should have shortened the key lookup time.)
> 
> Another bpf prog is with the new BPF_MAP_TYPE_SK_STORAGE.
> 
> Both are storing a "u32 cnt", do a lookup on "egress_skb/cgroup" for
> each egress skb and then bump the cnt.  netperf is used to drive
> data with 4096 connected UDP sockets.
> 
> BPF_MAP_TYPE_HASH with a modifier verifier (152ns per bpf run)
> 27: cgroup_skb  name egress_sk_map  tag 74f56e832918070b run_time_ns 58280107540 run_cnt 381347633
>     loaded_at 2019-04-15T13:46:39-0700  uid 0
>     xlated 344B  jited 258B  memlock 4096B  map_ids 16
>     btf_id 5
> 
> BPF_MAP_TYPE_SK_STORAGE in this patch (66ns per bpf run)
> 30: cgroup_skb  name egress_sk_stora  tag d4aa70984cc7bbf6 run_time_ns 25617093319 run_cnt 390989739
>     loaded_at 2019-04-15T13:47:54-0700  uid 0
>     xlated 168B  jited 156B  memlock 4096B  map_ids 17
>     btf_id 6
> 
> Here is a high-level picture on how are the objects organized:
> 
>        sk
>     ┌──────┐
>     │      │
>     │      │
>     │      │
>     │*sk_bpf_storage─────▶ bpf_sk_storage
>     └──────┘                 ┌───────┐
>                  ┌───────────┤ list  │
>                  │           │       │
>                  │           │       │
>                  │           │       │
>                  │           └───────┘
>                  │
>                  │     elem
>                  │  ┌────────┐
>                  ├─▶│ snode  │
>                  │  ├────────┤
>                  │  │  data  │          bpf_map
>                  │  ├────────┤        ┌─────────┐
>                  │  │map_node│◀─┬─────┤  list   │
>                  │  └────────┘  │     │         │
>                  │              │     │         │
>                  │     elem     │     │         │
>                  │  ┌────────┐  │     └─────────┘
>                  └─▶│ snode  │  │
>                     ├────────┤  │
>    bpf_map          │  data  │  │
>  ┌─────────┐        ├────────┤  │
>  │  list   ├───────▶│map_node│  │
>  │         │        └────────┘  │
>  │         │                    │
>  │         │           elem     │
>  └─────────┘        ┌────────┐  │
>                  ┌─▶│ snode  │  │
>                  │  ├────────┤  │
>                  │  │  data  │  │
>                  │  ├────────┤  │
>                  │  │map_node│◀─┘
>                  │  └────────┘
>                  │
>                  │
>                  │          ┌───────┐
>      sk          └──────────│ list  │
>   ┌──────┐                  │       │
>   │      │                  │       │
>   │      │                  │       │
>   │      │                  └───────┘
>   │*sk_bpf_storage───────▶bpf_sk_storage
>   └──────┘
That graph looks awesome, how did you do that? :-)

> Signed-off-by: Martin KaFai Lau <kafai@...com>
> ---
>  include/linux/bpf.h          |   2 +
>  include/linux/bpf_types.h    |   1 +
>  include/net/bpf_sk_storage.h |  13 +
>  include/net/sock.h           |   5 +
>  include/uapi/linux/bpf.h     |  44 +-
>  kernel/bpf/syscall.c         |   3 +-
>  kernel/bpf/verifier.c        |  27 +-
>  net/bpf/test_run.c           |   2 +
>  net/core/Makefile            |   1 +
>  net/core/bpf_sk_storage.c    | 796 +++++++++++++++++++++++++++++++++++
>  net/core/filter.c            |  12 +
>  net/core/sock.c              |   5 +
>  12 files changed, 906 insertions(+), 5 deletions(-)
>  create mode 100644 include/net/bpf_sk_storage.h
>  create mode 100644 net/core/bpf_sk_storage.c
> 
> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index f15432d90728..0d2788beacd2 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -184,6 +184,7 @@ enum bpf_arg_type {
>  	ARG_PTR_TO_MAP_KEY,	/* pointer to stack used as map key */
>  	ARG_PTR_TO_MAP_VALUE,	/* pointer to stack used as map value */
>  	ARG_PTR_TO_UNINIT_MAP_VALUE,	/* pointer to valid memory used to store a map value */
> +	ARG_PTR_TO_MAP_VALUE_OR_NULL,	/* pointer to stack used as map value or NULL */
>  
>  	/* the following constraints used to prototype bpf_memcmp() and other
>  	 * functions that access data on eBPF program stack
> @@ -204,6 +205,7 @@ enum bpf_arg_type {
>  	ARG_PTR_TO_SOCK_COMMON,	/* pointer to sock_common */
>  	ARG_PTR_TO_INT,		/* pointer to int */
>  	ARG_PTR_TO_LONG,	/* pointer to long */
> +	ARG_PTR_TO_SOCKET,	/* pointer to bpf_sock (fullsock) */
>  };
>  
>  /* type of values returned from helper functions */
> diff --git a/include/linux/bpf_types.h b/include/linux/bpf_types.h
> index d26991a16894..eb1e4f867a5e 100644
> --- a/include/linux/bpf_types.h
> +++ b/include/linux/bpf_types.h
> @@ -60,6 +60,7 @@ BPF_MAP_TYPE(BPF_MAP_TYPE_ARRAY_OF_MAPS, array_of_maps_map_ops)
>  BPF_MAP_TYPE(BPF_MAP_TYPE_HASH_OF_MAPS, htab_of_maps_map_ops)
>  #ifdef CONFIG_NET
>  BPF_MAP_TYPE(BPF_MAP_TYPE_DEVMAP, dev_map_ops)
> +BPF_MAP_TYPE(BPF_MAP_TYPE_SK_STORAGE, sk_storage_map_ops)
>  #if defined(CONFIG_BPF_STREAM_PARSER)
>  BPF_MAP_TYPE(BPF_MAP_TYPE_SOCKMAP, sock_map_ops)
>  BPF_MAP_TYPE(BPF_MAP_TYPE_SOCKHASH, sock_hash_ops)
> diff --git a/include/net/bpf_sk_storage.h b/include/net/bpf_sk_storage.h
> new file mode 100644
> index 000000000000..b9dcb02e756b
> --- /dev/null
> +++ b/include/net/bpf_sk_storage.h
> @@ -0,0 +1,13 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/* Copyright (c) 2019 Facebook */
> +#ifndef _BPF_SK_STORAGE_H
> +#define _BPF_SK_STORAGE_H
> +
> +struct sock;
> +
> +void bpf_sk_storage_free(struct sock *sk);
> +
> +extern const struct bpf_func_proto bpf_sk_storage_get_proto;
> +extern const struct bpf_func_proto bpf_sk_storage_delete_proto;
> +
> +#endif /* _BPF_SK_STORAGE_H */
> diff --git a/include/net/sock.h b/include/net/sock.h
> index 784cd19d5ff7..4d208c0f9c14 100644
> --- a/include/net/sock.h
> +++ b/include/net/sock.h
> @@ -236,6 +236,8 @@ struct sock_common {
>  	/* public: */
>  };
>  
> +struct bpf_sk_storage;
> +
>  /**
>    *	struct sock - network layer representation of sockets
>    *	@__sk_common: shared layout with inet_timewait_sock
> @@ -510,6 +512,9 @@ struct sock {
>  #endif
>  	void                    (*sk_destruct)(struct sock *sk);
>  	struct sock_reuseport __rcu	*sk_reuseport_cb;
> +#ifdef CONFIG_BPF_SYSCALL
> +	struct bpf_sk_storage __rcu	*sk_bpf_storage;
> +#endif
>  	struct rcu_head		sk_rcu;
>  };
>  
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index eaf2d3284248..080ff8313ced 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -133,6 +133,7 @@ enum bpf_map_type {
>  	BPF_MAP_TYPE_PERCPU_CGROUP_STORAGE,
>  	BPF_MAP_TYPE_QUEUE,
>  	BPF_MAP_TYPE_STACK,
> +	BPF_MAP_TYPE_SK_STORAGE,
>  };
>  
>  /* Note that tracing related programs such as
> @@ -2629,6 +2630,42 @@ union bpf_attr {
>   *		was provided.
>   *
>   *		**-ERANGE** if resulting value was out of range.
> + *
> + * void *bpf_sk_storage_get(struct bpf_map *map, struct bpf_sock *sk, void *value, u64 flags)
> + *	Description
> + *		Get a bpf-local-storage from a sk.
> + *
> + *		Logically, it could be thought of getting the value from
> + *		a *map* with *sk* as the **key**.  From this
> + *		perspective,  the usage is not much different from
> + *		**bpf_map_lookup_elem(map, &sk)** except this
> + *		helper enforces the key must be a **bpf_fullsock()**
> + *		and the map must be a BPF_MAP_TYPE_SK_STORAGE also.
> + *
> + *		Underneath, the value is stored locally at *sk* instead of
> + *		the map.  The *map* is used as the bpf-local-storage **type**.
> + *		The bpf-local-storage **type** (i.e. the *map*) is searched
> + *		against all bpf-local-storages residing at sk.
> + *
> + *		An optional *flags* (BPF_SK_STORAGE_GET_F_CREATE) can be
> + *		used such that a new bpf-local-storage will be
> + *		created if one does not exist.  *value* can be used
> + *		together with BPF_SK_STORAGE_GET_F_CREATE to specify
> + *		the initial value of a bpf-local-storage.  If *value* is
> + *		NULL, the new bpf-local-storage will be zero initialized.
> + *	Return
> + *		A bpf-local-storage pointer is returned on success.
> + *
> + *		**NULL** if not found or there was an error in adding
> + *		a new bpf-local-storage.
> + *
> + * int bpf_sk_storage_delete(struct bpf_map *map, struct bpf_sock *sk)
> + *	Description
> + *		Delete a bpf-local-storage from a sk.
> + *	Return
> + *		0 on success.
> + *
> + *		**-ENOENT** if the bpf-local-storage cannot be found.
>   */
>  #define __BPF_FUNC_MAPPER(FN)		\
>  	FN(unspec),			\
> @@ -2737,7 +2774,9 @@ union bpf_attr {
>  	FN(sysctl_get_new_value),	\
>  	FN(sysctl_set_new_value),	\
>  	FN(strtol),			\
> -	FN(strtoul),
> +	FN(strtoul),			\
> +	FN(sk_storage_get),		\
> +	FN(sk_storage_delete),
>  
>  /* integer value in 'imm' field of BPF_CALL instruction selects which helper
>   * function eBPF program intends to call
> @@ -2813,6 +2852,9 @@ enum bpf_func_id {
>  /* BPF_FUNC_sysctl_get_name flags. */
>  #define BPF_F_SYSCTL_BASE_NAME		(1ULL << 0)
>  
> +/* BPF_FUNC_sk_storage_get flags */
> +#define BPF_SK_STORAGE_GET_F_CREATE	(1ULL << 0)
> +
>  /* Mode for BPF_FUNC_skb_adjust_room helper. */
>  enum bpf_adj_room_mode {
>  	BPF_ADJ_ROOM_NET,
> diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
> index 92c9b8a32b50..69c9cb7cf5f7 100644
> --- a/kernel/bpf/syscall.c
> +++ b/kernel/bpf/syscall.c
> @@ -526,7 +526,8 @@ static int map_check_btf(struct bpf_map *map, const struct btf *btf,
>  			return -EACCES;
>  		if (map->map_type != BPF_MAP_TYPE_HASH &&
>  		    map->map_type != BPF_MAP_TYPE_ARRAY &&
> -		    map->map_type != BPF_MAP_TYPE_CGROUP_STORAGE)
> +		    map->map_type != BPF_MAP_TYPE_CGROUP_STORAGE &&
> +		    map->map_type != BPF_MAP_TYPE_SK_STORAGE)
>  			return -ENOTSUPP;
>  		if (map->spin_lock_off + sizeof(struct bpf_spin_lock) >
>  		    map->value_size) {
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index dc01abd27849..6ed13a03cdec 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -2525,10 +2525,15 @@ static int check_func_arg(struct bpf_verifier_env *env, u32 regno,
>  
>  	if (arg_type == ARG_PTR_TO_MAP_KEY ||
>  	    arg_type == ARG_PTR_TO_MAP_VALUE ||
> -	    arg_type == ARG_PTR_TO_UNINIT_MAP_VALUE) {
> +	    arg_type == ARG_PTR_TO_UNINIT_MAP_VALUE ||
> +	    arg_type == ARG_PTR_TO_MAP_VALUE_OR_NULL) {
>  		expected_type = PTR_TO_STACK;
> -		if (!type_is_pkt_pointer(type) && type != PTR_TO_MAP_VALUE &&
> -		    type != expected_type)
> +		if (register_is_null(reg) &&
> +		    arg_type == ARG_PTR_TO_MAP_VALUE_OR_NULL)
> +			/* final test in check_stack_boundary() */;
> +		else if (!type_is_pkt_pointer(type) &&
> +			 type != PTR_TO_MAP_VALUE &&
> +			 type != expected_type)
>  			goto err_type;
>  	} else if (arg_type == ARG_CONST_SIZE ||
>  		   arg_type == ARG_CONST_SIZE_OR_ZERO) {
> @@ -2560,6 +2565,10 @@ static int check_func_arg(struct bpf_verifier_env *env, u32 regno,
>  			}
>  			meta->ref_obj_id = reg->ref_obj_id;
>  		}
> +	} else if (arg_type == ARG_PTR_TO_SOCKET) {
> +		expected_type = PTR_TO_SOCKET;
> +		if (type != expected_type)
> +			goto err_type;
>  	} else if (arg_type == ARG_PTR_TO_SPIN_LOCK) {
>  		if (meta->func_id == BPF_FUNC_spin_lock) {
>  			if (process_spin_lock(env, regno, true))
> @@ -2617,6 +2626,8 @@ static int check_func_arg(struct bpf_verifier_env *env, u32 regno,
>  					      meta->map_ptr->key_size, false,
>  					      NULL);
>  	} else if (arg_type == ARG_PTR_TO_MAP_VALUE ||
> +		   (arg_type == ARG_PTR_TO_MAP_VALUE_OR_NULL &&
> +		    !register_is_null(reg)) ||
>  		   arg_type == ARG_PTR_TO_UNINIT_MAP_VALUE) {
>  		/* bpf_map_xxx(..., map_ptr, ..., value) call:
>  		 * check [value, value + map->value_size) validity
> @@ -2766,6 +2777,11 @@ static int check_map_func_compatibility(struct bpf_verifier_env *env,
>  		    func_id != BPF_FUNC_map_push_elem)
>  			goto error;
>  		break;
> +	case BPF_MAP_TYPE_SK_STORAGE:
> +		if (func_id != BPF_FUNC_sk_storage_get &&
> +		    func_id != BPF_FUNC_sk_storage_delete)
> +			goto error;
> +		break;
>  	default:
>  		break;
>  	}
> @@ -2829,6 +2845,11 @@ static int check_map_func_compatibility(struct bpf_verifier_env *env,
>  		    map->map_type != BPF_MAP_TYPE_STACK)
>  			goto error;
>  		break;
> +	case BPF_FUNC_sk_storage_get:
> +	case BPF_FUNC_sk_storage_delete:
> +		if (map->map_type != BPF_MAP_TYPE_SK_STORAGE)
> +			goto error;
> +		break;
>  	default:
>  		break;
>  	}
> diff --git a/net/bpf/test_run.c b/net/bpf/test_run.c
> index 8606e5aef0b6..8c9331913753 100644
> --- a/net/bpf/test_run.c
> +++ b/net/bpf/test_run.c
> @@ -10,6 +10,7 @@
>  #include <linux/etherdevice.h>
>  #include <linux/filter.h>
>  #include <linux/sched/signal.h>
> +#include <net/bpf_sk_storage.h>
>  #include <net/sock.h>
>  #include <net/tcp.h>
>  
> @@ -331,6 +332,7 @@ int bpf_prog_test_run_skb(struct bpf_prog *prog, const union bpf_attr *kattr,
>  				     sizeof(struct __sk_buff));
>  out:
>  	kfree_skb(skb);
> +	bpf_sk_storage_free(sk);
>  	kfree(sk);
>  	kfree(ctx);
>  	return ret;
> diff --git a/net/core/Makefile b/net/core/Makefile
> index f97d6254e564..a104dc8faafc 100644
> --- a/net/core/Makefile
> +++ b/net/core/Makefile
> @@ -34,3 +34,4 @@ obj-$(CONFIG_HWBM) += hwbm.o
>  obj-$(CONFIG_NET_DEVLINK) += devlink.o
>  obj-$(CONFIG_GRO_CELLS) += gro_cells.o
>  obj-$(CONFIG_FAILOVER) += failover.o
> +obj-$(CONFIG_BPF_SYSCALL) += bpf_sk_storage.o
> diff --git a/net/core/bpf_sk_storage.c b/net/core/bpf_sk_storage.c
> new file mode 100644
> index 000000000000..c01d4b9207e0
> --- /dev/null
> +++ b/net/core/bpf_sk_storage.c
> @@ -0,0 +1,796 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/* Copyright (c) 2019 Facebook  */
> +#include <linux/rculist.h>
> +#include <linux/list.h>
> +#include <linux/hash.h>
> +#include <linux/types.h>
> +#include <linux/spinlock.h>
> +#include <linux/bpf.h>
> +#include <net/bpf_sk_storage.h>
> +#include <net/sock.h>
> +#include <uapi/linux/btf.h>
> +
> +static atomic_t cache_idx;
Can this be made per-bpf_sk_storage? And be incremented in the slow path
of __sk_storage_lookup?

> +struct bucket {
> +	struct hlist_head list;
> +	raw_spinlock_t lock;
> +};
> +
> +/* Thp map is not the primary owner of a bpf_sk_storage_elem.
> + * Instead, the sk->sk_bpf_storage is.
> + *
> + * The map (bpf_sk_storage_map) is for two purposes
> + * 1. Define the size of the "sk local storage".  It is
> + *    the map's value_size.
> + *
> + * 2. Maintain a list to keep track of all elems such
> + *    that they can be cleaned up during the map destruction.
> + *
> + * When a bpf local storage is being looked up for a
> + * particular sk,  the "bpf_map" pointer is actually used
> + * as the "key" to search in the list of elem in
> + * sk->sk_bpf_storage.
> + *
> + * Hence, consider sk->sk_bpf_storage is the mini-map
> + * with the "bpf_map" pointer as the searching key.
> + */
> +struct bpf_sk_storage_map {
> +	struct bpf_map map;
> +	/* Lookup elem does not require accessing the map.
> +	 *
> +	 * Updating/Deleting requires a bucket lock to
> +	 * link/unlink the elem from the map.  Having
> +	 * multiple buckets to improve contention.
> +	 */
> +	struct bucket *buckets;
> +	u32 bucket_log;
> +	u16 elem_size;
> +	u16 cache_idx;
> +};
> +
> +struct bpf_sk_storage_data {
> +	/* smap is used as the searching key when looking up
> +	 * from sk->sk_bpf_storage.
> +	 *
> +	 * Put it in the same cacheline as the data to minimize
> +	 * the number of cachelines access during the cache hit case.
> +	 */
> +	struct bpf_sk_storage_map __rcu *smap;
> +	u8 data[0] __aligned(8);
> +};
> +
> +/* Linked to bpf_sk_storage and bpf_sk_storage_map */
> +struct bpf_sk_storage_elem {
> +	struct hlist_node map_node;	/* Linked to bpf_sk_storage_map */
> +	struct hlist_node snode;	/* Linked to bpf_sk_storage */
> +	struct bpf_sk_storage __rcu *sk_storage;
> +	struct rcu_head rcu;
> +	/* 8 bytes hole */
> +	/* The data is stored in aother cacheline to minimize
> +	 * the number of cachelines access during a cache hit.
> +	 */
> +	struct bpf_sk_storage_data sdata ____cacheline_aligned;
> +};
> +
> +#define SELEM(_SDATA) container_of((_SDATA), struct bpf_sk_storage_elem, sdata)
> +#define SDATA(_SELEM) (&(_SELEM)->sdata)
> +#define BPF_SK_STORAGE_CACHE_SIZE	16
Is it a number of concurrent programs sk can "efficiently" access?
Why 16? Maybe add a comment?

> +struct bpf_sk_storage {
> +	struct bpf_sk_storage_data __rcu *cache[BPF_SK_STORAGE_CACHE_SIZE];
> +	struct hlist_head list;	/* List of bpf_sk_storage_elem */
> +	struct sock *sk;	/* The sk that owns the the above "list" of
> +				 * bpf_sk_storage_elem.
> +				 */
> +	struct rcu_head rcu;
> +	raw_spinlock_t lock;	/* Protect adding/removing from the "list" */
> +};
> +
> +static struct bucket *select_bucket(struct bpf_sk_storage_map *smap,
> +				    struct bpf_sk_storage_elem *selem)
> +{
> +	return &smap->buckets[hash_ptr(selem, smap->bucket_log)];
> +}
> +
> +static int omem_charge(struct sock *sk, unsigned int size)
> +{
> +	/* same check as in sock_kmalloc() */
> +	if (size <= sysctl_optmem_max &&
> +	    atomic_read(&sk->sk_omem_alloc) + size < sysctl_optmem_max) {
> +		atomic_add(size, &sk->sk_omem_alloc);
> +		return 0;
> +	}
> +
> +	return -ENOMEM;
> +}
> +
> +static bool selem_linked_to_sk(const struct bpf_sk_storage_elem *selem)
> +{
> +	return !hlist_unhashed(&selem->snode);
> +}
> +
> +static bool selem_linked_to_map(const struct bpf_sk_storage_elem *selem)
> +{
> +	return !hlist_unhashed(&selem->map_node);
> +}
> +
> +static struct bpf_sk_storage_elem *selem_alloc(struct bpf_sk_storage_map *smap,
> +					       struct sock *sk, void *value,
> +					       bool charge_omem)
> +{
> +	struct bpf_sk_storage_elem *selem;
> +
> +	if (charge_omem && omem_charge(sk, smap->elem_size))
> +		return NULL;
> +
> +	selem = kzalloc(smap->elem_size, GFP_ATOMIC | __GFP_NOWARN);
> +	if (selem) {
> +		if (value)
> +			memcpy(SDATA(selem)->data, value, smap->map.value_size);
> +		return selem;
> +	}
> +
> +	if (charge_omem)
> +		atomic_sub(smap->elem_size, &sk->sk_omem_alloc);
> +
> +	return NULL;
> +}
> +
> +/* sk_storage->lock must be held and selem->sk_storage == sk_storage.
> + * The caller must ensure selem->smap is still valid to be
> + * dereferenced for its smap->elem_size and smap->cache_idx.
> + */
> +static bool __selem_unlink_sk(struct bpf_sk_storage *sk_storage,
> +			      struct bpf_sk_storage_elem *selem,
> +			      bool uncharge_omem)
> +{
> +	struct bpf_sk_storage_map *smap;
> +	bool free_sk_storage;
> +	struct sock *sk;
> +
> +	smap = rcu_dereference(SDATA(selem)->smap);
> +	sk = sk_storage->sk;
> +
> +	/* All uncharging on sk->sk_omem_alloc must be done first.
> +	 * sk may be freed once the last selem is unlinked from sk_storage.
> +	 */
> +	if (uncharge_omem)
> +		atomic_sub(smap->elem_size, &sk->sk_omem_alloc);
> +
> +	free_sk_storage = hlist_is_singular_node(&selem->snode,
> +						 &sk_storage->list);
> +	if (free_sk_storage) {
> +		atomic_sub(sizeof(struct bpf_sk_storage), &sk->sk_omem_alloc);
> +		sk_storage->sk = NULL;
> +		/* After this RCU_INIT, sk may be freed and cannot be used */
> +		RCU_INIT_POINTER(sk->sk_bpf_storage, NULL);
> +
> +		/* sk_storage is not freed now.  sk_storage->lock is
> +		 * still held and raw_spin_unlock_bh(&sk_storage->lock)
> +		 * will be done by the caller.
> +		 *
> +		 * Although the unlock will be done under
> +		 * rcu_read_lock(),  it is more intutivie to
> +		 * read if kfree_rcu(sk_storage, rcu) is done
> +		 * after the raw_spin_unlock_bh(&sk_storage->lock).
> +		 *
> +		 * Hence, a "bool free_sk_storage" is returned
> +		 * to the caller which then calls the kfree_rcu()
> +		 * after unlock.
> +		 */
> +	}
> +	hlist_del_init_rcu(&selem->snode);
> +	if (rcu_access_pointer(sk_storage->cache[smap->cache_idx]) ==
> +	    SDATA(selem))
> +		RCU_INIT_POINTER(sk_storage->cache[smap->cache_idx], NULL);
> +
> +	kfree_rcu(selem, rcu);
> +
> +	return free_sk_storage;
> +}
> +
> +static void selem_unlink_sk(struct bpf_sk_storage_elem *selem)
> +{
> +	struct bpf_sk_storage *sk_storage;
> +	bool free_sk_storage = false;
> +
> +	if (unlikely(!selem_linked_to_sk(selem)))
> +		/* selem has already been unlinked from sk */
> +		return;
> +
> +	sk_storage = rcu_dereference(selem->sk_storage);
> +	raw_spin_lock_bh(&sk_storage->lock);
> +	if (likely(selem_linked_to_sk(selem)))
> +		free_sk_storage = __selem_unlink_sk(sk_storage, selem, true);
> +	raw_spin_unlock_bh(&sk_storage->lock);
> +
> +	if (free_sk_storage)
> +		kfree_rcu(sk_storage, rcu);
> +}
> +
> +/* sk_storage->lock must be held and sk_storage->list cannot be empty */
> +static void __selem_link_sk(struct bpf_sk_storage *sk_storage,
> +			    struct bpf_sk_storage_elem *selem)
> +{
> +	RCU_INIT_POINTER(selem->sk_storage, sk_storage);
> +	hlist_add_head(&selem->snode, &sk_storage->list);
> +}
> +
> +static void selem_unlink_map(struct bpf_sk_storage_elem *selem)
> +{
> +	struct bpf_sk_storage_map *smap;
> +	struct bucket *b;
> +
> +	if (unlikely(!selem_linked_to_map(selem)))
> +		/* selem has already be unlinked from smap */
> +		return;
> +
> +	smap = rcu_dereference(SDATA(selem)->smap);
> +	b = select_bucket(smap, selem);
> +	raw_spin_lock_bh(&b->lock);
> +	if (likely(selem_linked_to_map(selem)))
> +		hlist_del_init_rcu(&selem->map_node);
> +	raw_spin_unlock_bh(&b->lock);
> +}
> +
> +static void selem_link_map(struct bpf_sk_storage_map *smap,
> +			   struct bpf_sk_storage_elem *selem)
> +{
> +	struct bucket *b = select_bucket(smap, selem);
> +
> +	raw_spin_lock_bh(&b->lock);
> +	RCU_INIT_POINTER(SDATA(selem)->smap, smap);
> +	hlist_add_head_rcu(&selem->map_node, &b->list);
> +	raw_spin_unlock_bh(&b->lock);
> +}
> +
> +static void selem_unlink(struct bpf_sk_storage_elem *selem)
> +{
> +	/* Always unlink from map before unlinking from sk_storage
> +	 * because selem will be freed after successfully unlinked from
> +	 * the sk_storage.
> +	 */
> +	selem_unlink_map(selem);
> +	selem_unlink_sk(selem);
> +}
> +
> +static struct bpf_sk_storage_data *
> +__sk_storage_lookup(struct bpf_sk_storage *sk_storage,
> +		    struct bpf_sk_storage_map *smap,
> +		    bool cacheit_lockit)
> +{
> +	struct bpf_sk_storage_data *sdata;
> +	struct bpf_sk_storage_elem *selem;
> +
> +	/* Fast path (cache hit) */
> +	sdata = rcu_dereference(sk_storage->cache[smap->cache_idx]);
> +	if (sdata && rcu_access_pointer(sdata->smap) == smap)
> +		return sdata;
> +
> +	/* Slow path (cache miss) */
> +	hlist_for_each_entry_rcu(selem, &sk_storage->list, snode)
> +		if (rcu_access_pointer(SDATA(selem)->smap) == smap)
> +			break;
> +
> +	if (!selem)
> +		return NULL;
> +
> +	sdata = SDATA(selem);
> +	if (cacheit_lockit) {
> +		/* spinlock is needed to avoid racing with the
> +		 * parallel delete.  Otherwise, publishing an already
> +		 * deleted sdata to the cache will become a use-after-free
> +		 * problem in the next __sk_storage_lookup().
> +		 */
> +		raw_spin_lock_bh(&sk_storage->lock);
> +		if (selem_linked_to_sk(selem))
> +			rcu_assign_pointer(sk_storage->cache[smap->cache_idx],
> +					   sdata);
> +		raw_spin_unlock_bh(&sk_storage->lock);
> +	}
> +
> +	return sdata;
> +}
> +
> +static struct bpf_sk_storage_data *
> +sk_storage_lookup(struct sock *sk, struct bpf_map *map, bool cacheit_lockit)
> +{
> +	struct bpf_sk_storage *sk_storage;
> +	struct bpf_sk_storage_map *smap;
> +
> +	sk_storage = rcu_dereference(sk->sk_bpf_storage);
> +	if (!sk_storage)
> +		return NULL;
> +
> +	smap = (struct bpf_sk_storage_map *)map;
> +	return __sk_storage_lookup(sk_storage, smap, cacheit_lockit);
> +}
> +
> +static int check_flags(const struct bpf_sk_storage_data *old_sdata,
> +		       u64 map_flags)
> +{
> +	if (old_sdata && (map_flags & ~BPF_F_LOCK) == BPF_NOEXIST)
> +		/* elem already exists */
> +		return -EEXIST;
> +
> +	if (!old_sdata && (map_flags & ~BPF_F_LOCK) == BPF_EXIST)
> +		/* elem doesn't exist, cannot update it */
> +		return -ENOENT;
> +
> +	return 0;
> +}
> +
> +static int sk_storage_alloc(struct sock *sk,
> +			    struct bpf_sk_storage_map *smap,
> +			    struct bpf_sk_storage_elem *first_selem)
> +{
> +	struct bpf_sk_storage *prev_sk_storage, *sk_storage;
> +	int err;
> +
> +	err = omem_charge(sk, sizeof(*sk_storage));
> +	if (err)
> +		return err;
> +
> +	sk_storage = kzalloc(sizeof(*sk_storage), GFP_ATOMIC | __GFP_NOWARN);
> +	if (!sk_storage) {
> +		err = -ENOMEM;
> +		goto uncharge;
> +	}
> +	INIT_HLIST_HEAD(&sk_storage->list);
> +	raw_spin_lock_init(&sk_storage->lock);
> +	sk_storage->sk = sk;
> +
> +	__selem_link_sk(sk_storage, first_selem);
> +	selem_link_map(smap, first_selem);
> +	/* Publish sk_storage to sk.  sk->sk_lock cannot be acquired.
> +	 * Hence, atomic ops is used to set sk->sk_bpf_storage
> +	 * from NULL to the newly allocated sk_storage ptr.
> +	 *
> +	 * From now on, the sk->sk_bpf_storage pointer is protected
> +	 * by the sk_storage->lock.  Hence,  when freeing
> +	 * the sk->sk_bpf_storage, the sk_storage->lock must
> +	 * be held before setting sk->sk_bpf_storage to NULL.
> +	 */
> +	prev_sk_storage = cmpxchg((struct bpf_sk_storage **)&sk->sk_bpf_storage,
> +				  NULL, sk_storage);
> +	if (unlikely(prev_sk_storage)) {
> +		selem_unlink_map(first_selem);
> +		err = -EAGAIN;
> +		goto uncharge;
> +
> +		/* Note that even first_selem was linked to smap's
> +		 * bucket->list, first_selem can be freed immediately
> +		 * (instead of kfree_rcu) because
> +		 * bpf_sk_storage_map_free() does a
> +		 * synchronize_rcu() before walking the bucket->list.
> +		 * Hence, no one is accessing selem from the
> +		 * bucket->list under rcu_read_lock().
> +		 */
> +	}
> +
> +	return 0;
> +
> +uncharge:
> +	kfree(sk_storage);
> +	atomic_sub(sizeof(*sk_storage), &sk->sk_omem_alloc);
> +	return err;
> +}
> +
> +/* sk cannot be going away because it is linking new elem
> + * to sk->sk_bpf_storage. (i.e. sk->sk_refcnt cannot be 0).
> + * Otherwise, it will become a leak (and other memory issues
> + * during map destruction).
> + */
> +static struct bpf_sk_storage_data *sk_storage_update(struct sock *sk,
> +						     struct bpf_map *map,
> +						     void *value,
> +						     u64 map_flags)
> +{
> +	struct bpf_sk_storage_data *old_sdata = NULL;
> +	struct bpf_sk_storage_elem *selem;
> +	struct bpf_sk_storage *sk_storage;
> +	struct bpf_sk_storage_map *smap;
> +	int err;
> +
> +	/* BPF_EXIST and BPF_NOEXIST cannot be both set */
> +	if (unlikely((map_flags & ~BPF_F_LOCK) > BPF_EXIST) ||
> +	    /* BPF_F_LOCK can only be used in a value with spin_lock */
> +	    unlikely((map_flags & BPF_F_LOCK) && !map_value_has_spin_lock(map)))
> +		return ERR_PTR(-EINVAL);
> +
> +	smap = (struct bpf_sk_storage_map *)map;
> +	sk_storage = rcu_dereference(sk->sk_bpf_storage);
> +	if (!sk_storage || hlist_empty(&sk_storage->list)) {
> +		/* Very first elem for this sk */
> +		err = check_flags(NULL, map_flags);
> +		if (err)
> +			return ERR_PTR(err);
> +
> +		selem = selem_alloc(smap, sk, value, true);
> +		if (!selem)
> +			return ERR_PTR(-ENOMEM);
> +
> +		err = sk_storage_alloc(sk, smap, selem);
> +		if (err) {
> +			kfree(selem);
> +			atomic_sub(smap->elem_size, &sk->sk_omem_alloc);
> +			return ERR_PTR(err);
> +		}
> +
> +		return SDATA(selem);
> +	}
> +
> +	if ((map_flags & BPF_F_LOCK) && !(map_flags & BPF_NOEXIST)) {
> +		/* Hoping to find an old_sdata to do inline update
> +		 * such that it can avoid taking the sk_storage->lock
> +		 * and changing the lists.
> +		 */
> +		old_sdata = __sk_storage_lookup(sk_storage, smap, false);
> +		err = check_flags(old_sdata, map_flags);
> +		if (err)
> +			return ERR_PTR(err);
> +		if (old_sdata && selem_linked_to_sk(SELEM(old_sdata))) {
> +			copy_map_value_locked(map, old_sdata->data,
> +					      value, false);
> +			return old_sdata;
> +		}
> +	}
> +
> +	raw_spin_lock_bh(&sk_storage->lock);
> +
> +	/* Recheck sk_storage->list under sk_storage->lock */
> +	if (unlikely(hlist_empty(&sk_storage->list))) {
> +		/* A parallel del is happening and sk_storage is going
> +		 * away.  It has just been checked before, so very
> +		 * unlikely.  Return instead of retry to keep things
> +		 * simple.
> +		 */
> +		err = -EAGAIN;
> +		goto unlock_err;
> +	}
> +
> +	old_sdata = __sk_storage_lookup(sk_storage, smap, false);
> +	err = check_flags(old_sdata, map_flags);
> +	if (err)
> +		goto unlock_err;
> +
> +	if (old_sdata && (map_flags & BPF_F_LOCK)) {
> +		copy_map_value_locked(map, old_sdata->data, value, false);
> +		selem = SELEM(old_sdata);
> +		goto unlock;
> +	}
> +
> +	/* sk_storage->lock is held.  Hence, we are sure
> +	 * we can unlink and uncharge the old_sdata successfully
> +	 * later.  Hence, instead of charging the new selem now
> +	 * and then uncharge the old selem later (which may cause
> +	 * a potential but unnecessary charge failure),  avoid taking
> +	 * a charge at all here (the "!old_sdata" check) and the
> +	 * old_sdata will not be uncharged later during __selem_unlink_sk().
> +	 */
> +	selem = selem_alloc(smap, sk, value, !old_sdata);
> +	if (!selem) {
> +		err = -ENOMEM;
> +		goto unlock_err;
> +	}
> +
> +	/* First, link the new selem to the map */
> +	selem_link_map(smap, selem);
> +
> +	/* Second, link (and publish) the new selem to sk_storage */
> +	__selem_link_sk(sk_storage, selem);
> +
> +	/* Third, remove old selem, SELEM(old_sdata) */
> +	if (old_sdata) {
> +		selem_unlink_map(SELEM(old_sdata));
> +		__selem_unlink_sk(sk_storage, SELEM(old_sdata), false);
> +	}
> +
> +unlock:
> +	raw_spin_unlock_bh(&sk_storage->lock);
> +	return SDATA(selem);
> +
> +unlock_err:
> +	raw_spin_unlock_bh(&sk_storage->lock);
> +	return ERR_PTR(err);
> +}
> +
> +static int sk_storage_delete(struct sock *sk, struct bpf_map *map)
> +{
> +	struct bpf_sk_storage_data *sdata;
> +
> +	sdata = sk_storage_lookup(sk, map, false);
> +	if (!sdata)
> +		return -ENOENT;
> +
> +	selem_unlink(SELEM(sdata));
Where is sdata (or I guess bpf_sk_storage_elem) kfree'd?

> +	return 0;
> +}
> +
> +/* Called by __sk_destruct() */
> +void bpf_sk_storage_free(struct sock *sk)
> +{
> +	struct bpf_sk_storage_elem *selem;
> +	struct bpf_sk_storage *sk_storage;
> +	bool free_sk_storage = false;
> +	struct hlist_node *n;
> +
> +	rcu_read_lock();
> +	sk_storage = rcu_dereference(sk->sk_bpf_storage);
> +	if (!sk_storage) {
> +		rcu_read_unlock();
> +		return;
> +	}
> +
> +	/* Netiher the bpf_prog nor the bpf-map's syscall
> +	 * could be modifying the sk_storage->list now.
> +	 * Thus, no elem can be added-to or deleted-from the
> +	 * sk_storage->list by the bpf_prog or by the bpf-map's syscall.
> +	 *
> +	 * It is racing with bpf_sk_storage_map_free() alone
> +	 * when unlinking elem from the sk_storage->list and
> +	 * the map's bucket->list.
> +	 */
> +	raw_spin_lock_bh(&sk_storage->lock);
> +	hlist_for_each_entry_safe(selem, n, &sk_storage->list, snode) {
> +		/* Always unlink from map before unlinking from
> +		 * sk_storage.
> +		 */
> +		selem_unlink_map(selem);
> +		free_sk_storage = __selem_unlink_sk(sk_storage, selem, true);
> +	}
> +	raw_spin_unlock_bh(&sk_storage->lock);
> +	rcu_read_unlock();
> +
> +	if (free_sk_storage)
> +		kfree_rcu(sk_storage, rcu);
> +}
> +
> +static void bpf_sk_storage_map_free(struct bpf_map *map)
> +{
> +	struct bpf_sk_storage_elem *selem;
> +	struct bpf_sk_storage_map *smap;
> +	struct bucket *b;
> +	unsigned int i;
> +
> +	smap = (struct bpf_sk_storage_map *)map;
> +
> +	synchronize_rcu();
> +
> +	/* bpf prog and the userspace can no longer access this map
> +	 * now.  No new selem (of this map) can be added
> +	 * to the sk->sk_bpf_storage or to the map bucket's list.
> +	 *
> +	 * The elem of this map can be cleaned up here
> +	 * or
> +	 * by bpf_sk_storage_free() during __sk_destruct().
> +	 */
> +	for (i = 0; i < (1U << smap->bucket_log); i++) {
> +		b = &smap->buckets[i];
> +
> +		rcu_read_lock();
> +		/* No one is adding to b->list now */
> +		while ((selem = hlist_entry_safe(rcu_dereference_raw(hlist_first_rcu(&b->list)),
> +						 struct bpf_sk_storage_elem,
> +						 map_node))) {
> +			selem_unlink(selem);
> +			cond_resched_rcu();
> +		}
> +		rcu_read_unlock();
> +	}
> +
> +	/* bpf_sk_storage_free() may still need to access the map.
> +	 * e.g. bpf_sk_storage_free() has unlinked selem from the map
> +	 * which then made the above while((selem = ...)) loop
> +	 * exited immediately.
> +	 *
> +	 * However, the bpf_sk_storage_free() still needs to access
> +	 * the smap->elem_size to do the uncharging in
> +	 * __selem_unlink_sk().
> +	 *
> +	 * Hence, wait another rcu grace period for the
> +	 * bpf_sk_storage_free() to finish.
> +	 */
> +	synchronize_rcu();
> +
> +	kvfree(smap->buckets);
> +	kfree(map);
> +}
> +
> +static struct bpf_map *bpf_sk_storage_map_alloc(union bpf_attr *attr)
> +{
> +	struct bpf_sk_storage_map *smap;
> +	unsigned int i;
> +	u32 nbuckets;
> +	u64 cost;
> +
> +	if (attr->map_flags != BPF_F_NO_PREALLOC || attr->max_entries ||
> +	    attr->key_size != sizeof(int) || !attr->value_size ||
> +	    /* Enforce BTF for userspace sk dumping */
> +	    !attr->btf_key_type_id || !attr->btf_value_type_id)
> +		return ERR_PTR(-EINVAL);
> +
> +	if (!capable(CAP_SYS_ADMIN))
> +		return ERR_PTR(-EPERM);
Any specific reason for CAP_SYS_ADMIN?

> +	if (attr->value_size >= KMALLOC_MAX_SIZE -
> +	    MAX_BPF_STACK - sizeof(struct bpf_sk_storage_elem) ||
> +	    /* selem->elem_size is a u16 */
> +	    attr->value_size > U16_MAX - sizeof(struct bpf_sk_storage_elem))
> +		return ERR_PTR(-E2BIG);
What's the rationale here for E2BIG? Same as htab_map_alloc_check?
Why not use .map_alloc_check btw?

> +	smap = kzalloc(sizeof(*smap), GFP_USER | __GFP_NOWARN);
> +	if (!smap)
> +		return ERR_PTR(-ENOMEM);
> +	bpf_map_init_from_attr(&smap->map, attr);
> +
> +	smap->bucket_log = ilog2(roundup_pow_of_two(num_possible_cpus()));
> +	nbuckets = 1U << smap->bucket_log;
> +	smap->buckets = kvcalloc(sizeof(*smap->buckets), nbuckets,
> +				 GFP_USER | __GFP_NOWARN);
> +	if (!smap->buckets) {
> +		kfree(smap);
> +		return ERR_PTR(-ENOMEM);
> +	}
> +	cost = sizeof(*smap->buckets) * nbuckets + sizeof(*smap);
> +
> +	for (i = 0; i < nbuckets; i++) {
> +		INIT_HLIST_HEAD(&smap->buckets[i].list);
> +		raw_spin_lock_init(&smap->buckets[i].lock);
> +	}
> +
> +	smap->elem_size = sizeof(struct bpf_sk_storage_elem) + attr->value_size;
> +	smap->cache_idx = (unsigned int)atomic_inc_return(&cache_idx) %
> +		BPF_SK_STORAGE_CACHE_SIZE;
> +	smap->map.pages = round_up(cost, PAGE_SIZE) >> PAGE_SHIFT;
> +
> +	return &smap->map;
> +}
> +
> +static int notsupp_get_next_key(struct bpf_map *map, void *key,
> +				void *next_key)
> +{
> +	return -ENOTSUPP;
> +}
> +
> +static int bpf_sk_storage_map_check_btf(const struct bpf_map *map,
> +					const struct btf *btf,
> +					const struct btf_type *key_type,
> +					const struct btf_type *value_type)
> +{
> +	u32 int_data;
> +
> +	if (BTF_INFO_KIND(key_type->info) != BTF_KIND_INT)
> +		return -EINVAL;
> +
> +	int_data = *(u32 *)(key_type + 1);
> +	if (BTF_INT_BITS(int_data) != 32 || BTF_INT_OFFSET(int_data))
> +		return -EINVAL;
> +
> +	return 0;
> +}
> +
> +static void *bpf_fd_sk_storage_lookup_elem(struct bpf_map *map, void *key)
> +{
> +	struct bpf_sk_storage_data *sdata;
> +	struct socket *sock;
> +	int fd, err;
> +
> +	fd = *(int *)key;
> +	sock = sockfd_lookup(fd, &err);
> +	if (sock) {
> +		sdata = sk_storage_lookup(sock->sk, map, true);
> +		sockfd_put(sock);
> +		return sdata ? sdata->data : NULL;
> +	}
> +
> +	return ERR_PTR(err);
> +}
> +
> +static int bpf_fd_sk_storage_update_elem(struct bpf_map *map, void *key,
> +					 void *value, u64 map_flags)
> +{
> +	struct bpf_sk_storage_data *sdata;
> +	struct socket *sock;
> +	int fd, err;
> +
> +	fd = *(int *)key;
> +	sock = sockfd_lookup(fd, &err);
> +	if (sock) {
> +		sdata = sk_storage_update(sock->sk, map, value, map_flags);
> +		sockfd_put(sock);
> +		return IS_ERR(sdata) ? PTR_ERR(sdata) : 0;
> +	}
> +
> +	return err;
> +}
> +
> +static int bpf_fd_sk_storage_delete_elem(struct bpf_map *map, void *key)
> +{
> +	struct socket *sock;
> +	int fd, err;
> +
> +	fd = *(int *)key;
> +	sock = sockfd_lookup(fd, &err);
> +	if (sock) {
> +		err = sk_storage_delete(sock->sk, map);
> +		sockfd_put(sock);
> +		return err;
> +	}
> +
> +	return err;
> +}
> +
> +BPF_CALL_4(bpf_sk_storage_get, struct bpf_map *, map, struct sock *, sk,
> +	   void *, value, u64, flags)
> +{
> +	struct bpf_sk_storage_data *sdata;
> +
> +	if (flags > BPF_SK_STORAGE_GET_F_CREATE)
> +		return (unsigned long)NULL;
> +
> +	sdata = sk_storage_lookup(sk, map, true);
> +	if (sdata)
> +		return (unsigned long)sdata->data;
> +
> +	if (flags == BPF_SK_STORAGE_GET_F_CREATE &&
> +	    /* Cannot add new elem to a going away sk.
> +	     * Otherwise, the new elem may become a leak
> +	     * (and also other memory issues during map
> +	     *  destruction).
> +	     */
> +	    refcount_inc_not_zero(&sk->sk_refcnt)) {
> +		sdata = sk_storage_update(sk, map, value, BPF_NOEXIST);
> +		/* sk must be a fullsock (guaranteed by verifier),
> +		 * so sock_gen_put() is unnecessary.
> +		 */
> +		sock_put(sk);
> +		return IS_ERR(sdata) ?
> +			(unsigned long)NULL : (unsigned long)sdata->data;
> +	}
> +
> +	return (unsigned long)NULL;
> +}
> +
> +BPF_CALL_2(bpf_sk_storage_delete, struct bpf_map *, map, struct sock *, sk)
> +{
> +	if (refcount_inc_not_zero(&sk->sk_refcnt)) {
> +		int err;
> +
> +		err = sk_storage_delete(sk, map);
> +		sock_put(sk);
> +		return err;
> +	}
> +
> +	return -ENOENT;
> +}
> +
> +const struct bpf_map_ops sk_storage_map_ops = {
> +	.map_alloc = bpf_sk_storage_map_alloc,
> +	.map_free = bpf_sk_storage_map_free,
> +	.map_get_next_key = notsupp_get_next_key,
> +	.map_lookup_elem = bpf_fd_sk_storage_lookup_elem,
> +	.map_update_elem = bpf_fd_sk_storage_update_elem,
> +	.map_delete_elem = bpf_fd_sk_storage_delete_elem,
> +	.map_check_btf = bpf_sk_storage_map_check_btf,
> +};
> +
> +const struct bpf_func_proto bpf_sk_storage_get_proto = {
> +	.func		= bpf_sk_storage_get,
> +	.gpl_only	= false,
> +	.ret_type	= RET_PTR_TO_MAP_VALUE_OR_NULL,
> +	.arg1_type	= ARG_CONST_MAP_PTR,
> +	.arg2_type	= ARG_PTR_TO_SOCKET,
> +	.arg3_type	= ARG_PTR_TO_MAP_VALUE_OR_NULL,
> +	.arg4_type	= ARG_ANYTHING,
> +};
> +
> +const struct bpf_func_proto bpf_sk_storage_delete_proto = {
> +	.func		= bpf_sk_storage_delete,
> +	.gpl_only	= false,
> +	.ret_type	= RET_INTEGER,
> +	.arg1_type	= ARG_CONST_MAP_PTR,
> +	.arg2_type	= ARG_PTR_TO_SOCKET,
> +};
> diff --git a/net/core/filter.c b/net/core/filter.c
> index 2f88baf39cc2..27b0dc01dc3f 100644
> --- a/net/core/filter.c
> +++ b/net/core/filter.c
> @@ -75,6 +75,7 @@
>  #include <net/seg6_local.h>
>  #include <net/lwtunnel.h>
>  #include <net/ipv6_stubs.h>
> +#include <net/bpf_sk_storage.h>
>  
>  /**
>   *	sk_filter_trim_cap - run a packet through a socket filter
> @@ -5903,6 +5904,9 @@ sk_filter_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
>  	}
>  }
>  
> +const struct bpf_func_proto bpf_sk_storage_get_proto __weak;
> +const struct bpf_func_proto bpf_sk_storage_delete_proto __weak;
> +
>  static const struct bpf_func_proto *
>  cg_skb_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
>  {
> @@ -5911,6 +5915,10 @@ cg_skb_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
>  		return &bpf_get_local_storage_proto;
>  	case BPF_FUNC_sk_fullsock:
>  		return &bpf_sk_fullsock_proto;
> +	case BPF_FUNC_sk_storage_get:
> +		return &bpf_sk_storage_get_proto;
> +	case BPF_FUNC_sk_storage_delete:
> +		return &bpf_sk_storage_delete_proto;
>  #ifdef CONFIG_INET
>  	case BPF_FUNC_tcp_sock:
>  		return &bpf_tcp_sock_proto;
> @@ -5992,6 +6000,10 @@ tc_cls_act_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
>  		return &bpf_skb_fib_lookup_proto;
>  	case BPF_FUNC_sk_fullsock:
>  		return &bpf_sk_fullsock_proto;
> +	case BPF_FUNC_sk_storage_get:
> +		return &bpf_sk_storage_get_proto;
> +	case BPF_FUNC_sk_storage_delete:
> +		return &bpf_sk_storage_delete_proto;
>  #ifdef CONFIG_XFRM
>  	case BPF_FUNC_skb_get_xfrm_state:
>  		return &bpf_skb_get_xfrm_state_proto;
> diff --git a/net/core/sock.c b/net/core/sock.c
> index 443b98d05f1e..9773be724aa9 100644
> --- a/net/core/sock.c
> +++ b/net/core/sock.c
> @@ -137,6 +137,7 @@
>  
>  #include <linux/filter.h>
>  #include <net/sock_reuseport.h>
> +#include <net/bpf_sk_storage.h>
>  
>  #include <trace/events/sock.h>
>  
> @@ -1709,6 +1710,10 @@ static void __sk_destruct(struct rcu_head *head)
>  
>  	sock_disable_timestamp(sk, SK_FLAGS_TIMESTAMP);
>  
> +#ifdef CONFIG_BPF_SYSCALL
> +	bpf_sk_storage_free(sk);
> +#endif
> +
>  	if (atomic_read(&sk->sk_omem_alloc))
>  		pr_debug("%s: optmem leakage (%d bytes) detected\n",
>  			 __func__, atomic_read(&sk->sk_omem_alloc));
> -- 
> 2.17.1
> 

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