bpf: add devmap, a map for storing net device references (546ac1ff) · Commits · 戴 / test

include/linux/bpf_types.h

+3 −0

Original line number	Diff line number	Diff line
		@@ -35,3 +35,6 @@ BPF_MAP_TYPE(BPF_MAP_TYPE_STACK_TRACE, stack_map_ops)
		#endif
		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)
		#endif

include/uapi/linux/bpf.h

+1 −0

Original line number	Diff line number	Diff line
		@@ -104,6 +104,7 @@ enum bpf_map_type {
		BPF_MAP_TYPE_LPM_TRIE,
		BPF_MAP_TYPE_ARRAY_OF_MAPS,
		BPF_MAP_TYPE_HASH_OF_MAPS,
		BPF_MAP_TYPE_DEVMAP,
		};

		enum bpf_prog_type {

kernel/bpf/Makefile

+3 −0

Original line number	Diff line number	Diff line
		@@ -2,6 +2,9 @@ obj-y := core.o

		obj-$(CONFIG_BPF_SYSCALL) += syscall.o verifier.o inode.o helpers.o
		obj-$(CONFIG_BPF_SYSCALL) += hashtab.o arraymap.o percpu_freelist.o bpf_lru_list.o lpm_trie.o map_in_map.o
		ifeq ($(CONFIG_NET),y)
		obj-$(CONFIG_BPF_SYSCALL) += devmap.o
		endif
		ifeq ($(CONFIG_PERF_EVENTS),y)
		obj-$(CONFIG_BPF_SYSCALL) += stackmap.o
		endif

kernel/bpf/devmap.c

0 → 100644

+264 −0

Original line number	Diff line number	Diff line
		/* Copyright (c) 2017 Covalent IO, Inc. http://covalent.io
		*
		* This program is free software; you can redistribute it and/or
		* modify it under the terms of version 2 of the GNU General Public
		* License as published by the Free Software Foundation.
		*
		* This program is distributed in the hope that it will be useful, but
		* WITHOUT ANY WARRANTY; without even the implied warranty of
		* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
		* General Public License for more details.
		*/

		/* Devmaps primary use is as a backend map for XDP BPF helper call
		* bpf_redirect_map(). Because XDP is mostly concerned with performance we
		* spent some effort to ensure the datapath with redirect maps does not use
		* any locking. This is a quick note on the details.
		*
		* We have three possible paths to get into the devmap control plane bpf
		* syscalls, bpf programs, and driver side xmit/flush operations. A bpf syscall
		* will invoke an update, delete, or lookup operation. To ensure updates and
		* deletes appear atomic from the datapath side xchg() is used to modify the
		* netdev_map array. Then because the datapath does a lookup into the netdev_map
		* array (read-only) from an RCU critical section we use call_rcu() to wait for
		* an rcu grace period before free'ing the old data structures. This ensures the
		* datapath always has a valid copy. However, the datapath does a "flush"
		* operation that pushes any pending packets in the driver outside the RCU
		* critical section. Each bpf_dtab_netdev tracks these pending operations using
		* an atomic per-cpu bitmap. The bpf_dtab_netdev object will not be destroyed
		* until all bits are cleared indicating outstanding flush operations have
		* completed.
		*
		* BPF syscalls may race with BPF program calls on any of the update, delete
		* or lookup operations. As noted above the xchg() operation also keep the
		* netdev_map consistent in this case. From the devmap side BPF programs
		* calling into these operations are the same as multiple user space threads
		* making system calls.
		*/
		#include <linux/bpf.h>
		#include <linux/jhash.h>
		#include <linux/filter.h>
		#include <linux/rculist_nulls.h>
		#include "percpu_freelist.h"
		#include "bpf_lru_list.h"
		#include "map_in_map.h"

		struct bpf_dtab_netdev {
		struct net_device *dev;
		int key;
		struct rcu_head rcu;
		struct bpf_dtab *dtab;
		};

		struct bpf_dtab {
		struct bpf_map map;
		struct bpf_dtab_netdev **netdev_map;
		};

		static struct bpf_map dev_map_alloc(union bpf_attr attr)
		{
		struct bpf_dtab *dtab;
		u64 cost;
		int err;

		/* check sanity of attributes */
		if (attr->max_entries == 0 \|\| attr->key_size != 4 \|\|
		attr->value_size != 4 \|\| attr->map_flags)
		return ERR_PTR(-EINVAL);

		/* if value_size is bigger, the user space won't be able to
		* access the elements.
		*/
		if (attr->value_size > KMALLOC_MAX_SIZE)
		return ERR_PTR(-E2BIG);

		dtab = kzalloc(sizeof(*dtab), GFP_USER);
		if (!dtab)
		return ERR_PTR(-ENOMEM);

		/* mandatory map attributes */
		dtab->map.map_type = attr->map_type;
		dtab->map.key_size = attr->key_size;
		dtab->map.value_size = attr->value_size;
		dtab->map.max_entries = attr->max_entries;
		dtab->map.map_flags = attr->map_flags;

		err = -ENOMEM;

		/* make sure page count doesn't overflow */
		cost = (u64) dtab->map.max_entries * sizeof(struct bpf_dtab_netdev *);
		if (cost >= U32_MAX - PAGE_SIZE)
		goto free_dtab;

		dtab->map.pages = round_up(cost, PAGE_SIZE) >> PAGE_SHIFT;

		/* if map size is larger than memlock limit, reject it early */
		err = bpf_map_precharge_memlock(dtab->map.pages);
		if (err)
		goto free_dtab;

		dtab->netdev_map = bpf_map_area_alloc(dtab->map.max_entries *
		sizeof(struct bpf_dtab_netdev *));
		if (!dtab->netdev_map)
		goto free_dtab;

		return &dtab->map;

		free_dtab:
		kfree(dtab);
		return ERR_PTR(err);
		}

		static void dev_map_free(struct bpf_map *map)
		{
		struct bpf_dtab *dtab = container_of(map, struct bpf_dtab, map);
		int i;

		/* At this point bpf_prog->aux->refcnt == 0 and this map->refcnt == 0,
		* so the programs (can be more than one that used this map) were
		* disconnected from events. Wait for outstanding critical sections in
		* these programs to complete. The rcu critical section only guarantees
		* no further reads against netdev_map. It does __not__ ensure pending
		* flush operations (if any) are complete.
		*/
		synchronize_rcu();

		for (i = 0; i < dtab->map.max_entries; i++) {
		struct bpf_dtab_netdev *dev;

		dev = dtab->netdev_map[i];
		if (!dev)
		continue;

		dev_put(dev->dev);
		kfree(dev);
		}

		/* At this point bpf program is detached and all pending operations
		* _must_ be complete
		*/
		bpf_map_area_free(dtab->netdev_map);
		kfree(dtab);
		}

		static int dev_map_get_next_key(struct bpf_map map, void key, void *next_key)
		{
		struct bpf_dtab *dtab = container_of(map, struct bpf_dtab, map);
		u32 index = key ? (u32 )key : U32_MAX;
		u32 next = (u32 )next_key;

		if (index >= dtab->map.max_entries) {
		*next = 0;
		return 0;
		}

		if (index == dtab->map.max_entries - 1)
		return -ENOENT;

		*next = index + 1;
		return 0;
		}

		/* rcu_read_lock (from syscall and BPF contexts) ensures that if a delete and/or
		* update happens in parallel here a dev_put wont happen until after reading the
		* ifindex.
		*/
		static void dev_map_lookup_elem(struct bpf_map map, void *key)
		{
		struct bpf_dtab *dtab = container_of(map, struct bpf_dtab, map);
		struct bpf_dtab_netdev *dev;
		u32 i = (u32 )key;

		if (i >= map->max_entries)
		return NULL;

		dev = READ_ONCE(dtab->netdev_map[i]);
		return dev ? &dev->dev->ifindex : NULL;
		}

		static void __dev_map_entry_free(struct rcu_head *rcu)
		{
		struct bpf_dtab_netdev *old_dev;

		old_dev = container_of(rcu, struct bpf_dtab_netdev, rcu);
		dev_put(old_dev->dev);
		kfree(old_dev);
		}

		static int dev_map_delete_elem(struct bpf_map map, void key)
		{
		struct bpf_dtab *dtab = container_of(map, struct bpf_dtab, map);
		struct bpf_dtab_netdev *old_dev;
		int k = (u32 )key;

		if (k >= map->max_entries)
		return -EINVAL;

		/* Use synchronize_rcu() here to ensure any rcu critical sections
		* have completed, but this does not guarantee a flush has happened
		* yet. Because driver side rcu_read_lock/unlock only protects the
		* running XDP program. However, for pending flush operations the
		* dev and ctx are stored in another per cpu map. And additionally,
		* the driver tear down ensures all soft irqs are complete before
		* removing the net device in the case of dev_put equals zero.
		*/
		old_dev = xchg(&dtab->netdev_map[k], NULL);
		if (old_dev)
		call_rcu(&old_dev->rcu, __dev_map_entry_free);
		return 0;
		}

		static int dev_map_update_elem(struct bpf_map map, void key, void *value,
		u64 map_flags)
		{
		struct bpf_dtab *dtab = container_of(map, struct bpf_dtab, map);
		struct net *net = current->nsproxy->net_ns;
		struct bpf_dtab_netdev dev, old_dev;
		u32 i = (u32 )key;
		u32 ifindex = (u32 )value;

		if (unlikely(map_flags > BPF_EXIST))
		return -EINVAL;

		if (unlikely(i >= dtab->map.max_entries))
		return -E2BIG;

		if (unlikely(map_flags == BPF_NOEXIST))
		return -EEXIST;

		if (!ifindex) {
		dev = NULL;
		} else {
		dev = kmalloc(sizeof(*dev), GFP_ATOMIC \| __GFP_NOWARN);
		if (!dev)
		return -ENOMEM;

		dev->dev = dev_get_by_index(net, ifindex);
		if (!dev->dev) {
		kfree(dev);
		return -EINVAL;
		}

		dev->key = i;
		dev->dtab = dtab;
		}

		/* Use call_rcu() here to ensure rcu critical sections have completed
		* Remembering the driver side flush operation will happen before the
		* net device is removed.
		*/
		old_dev = xchg(&dtab->netdev_map[i], dev);
		if (old_dev)
		call_rcu(&old_dev->rcu, __dev_map_entry_free);

		return 0;
		}

		const struct bpf_map_ops dev_map_ops = {
		.map_alloc = dev_map_alloc,
		.map_free = dev_map_free,
		.map_get_next_key = dev_map_get_next_key,
		.map_lookup_elem = dev_map_lookup_elem,
		.map_update_elem = dev_map_update_elem,
		.map_delete_elem = dev_map_delete_elem,
		};

kernel/bpf/verifier.c

+8 −0

Original line number	Diff line number	Diff line
		@@ -1276,6 +1276,14 @@ static int check_map_func_compatibility(struct bpf_map *map, int func_id)
		func_id != BPF_FUNC_current_task_under_cgroup)
		goto error;
		break;
		/* devmap returns a pointer to a live net_device ifindex that we cannot
		* allow to be modified from bpf side. So do not allow lookup elements
		* for now.
		*/
		case BPF_MAP_TYPE_DEVMAP:
		if (func_id == BPF_FUNC_map_lookup_elem)
		goto error;
		break;
		case BPF_MAP_TYPE_ARRAY_OF_MAPS:
		case BPF_MAP_TYPE_HASH_OF_MAPS:
		if (func_id != BPF_FUNC_map_lookup_elem)

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