netdevsim: bpf: support fake map offload

Add to netdevsim ability to pretend it's offloading BPF maps.
We only allow allocation of tiny 2 entry maps, to keep things
simple.  Mutex lock may seem heavy for the operations we
perform, but we want to make sure callbacks can sleep.
Signed-off-by: NJakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: NDaniel Borkmann <daniel@iogearbox.net>

drivers/net/netdevsim/bpf.c

@@ -17,6 +17,7 @@
 #include <linux/bpf_verifier.h>
 #include <linux/debugfs.h>
 #include <linux/kernel.h>
+#include <linux/mutex.h>
 #include <linux/rtnetlink.h>
 #include <net/pkt_cls.h>
 
@@ -31,6 +32,19 @@ struct nsim_bpf_bound_prog {
 	struct list_head l;
 };
 
+#define NSIM_BPF_MAX_KEYS		2
+
+struct nsim_bpf_bound_map {
+	struct netdevsim *ns;
+	struct bpf_offloaded_map *map;
+	struct mutex mutex;
+	struct nsim_map_entry {
+		void *key;
+		void *value;
+	} entry[NSIM_BPF_MAX_KEYS];
+	struct list_head l;
+};
+
 static int nsim_debugfs_bpf_string_read(struct seq_file *file, void *data)
 {
 	const char **str = file->private;
@@ -284,6 +298,224 @@ nsim_setup_prog_hw_checks(struct netdevsim *ns, struct netdev_bpf *bpf)
 	return 0;
 }
 
+static bool
+nsim_map_key_match(struct bpf_map *map, struct nsim_map_entry *e, void *key)
+{
+	return e->key && !memcmp(key, e->key, map->key_size);
+}
+
+static int nsim_map_key_find(struct bpf_offloaded_map *offmap, void *key)
+{
+	struct nsim_bpf_bound_map *nmap = offmap->dev_priv;
+	unsigned int i;
+
+	for (i = 0; i < ARRAY_SIZE(nmap->entry); i++)
+		if (nsim_map_key_match(&offmap->map, &nmap->entry[i], key))
+			return i;
+
+	return -ENOENT;
+}
+
+static int
+nsim_map_alloc_elem(struct bpf_offloaded_map *offmap, unsigned int idx)
+{
+	struct nsim_bpf_bound_map *nmap = offmap->dev_priv;
+
+	nmap->entry[idx].key = kmalloc(offmap->map.key_size, GFP_USER);
+	if (!nmap->entry[idx].key)
+		return -ENOMEM;
+	nmap->entry[idx].value = kmalloc(offmap->map.value_size, GFP_USER);
+	if (!nmap->entry[idx].value) {
+		kfree(nmap->entry[idx].key);
+		nmap->entry[idx].key = NULL;
+		return -ENOMEM;
+	}
+
+	return 0;
+}
+
+static int
+nsim_map_get_next_key(struct bpf_offloaded_map *offmap,
+		      void *key, void *next_key)
+{
+	struct nsim_bpf_bound_map *nmap = offmap->dev_priv;
+	int idx = -ENOENT;
+
+	mutex_lock(&nmap->mutex);
+
+	if (key)
+		idx = nsim_map_key_find(offmap, key);
+	if (idx == -ENOENT)
+		idx = 0;
+	else
+		idx++;
+
+	for (; idx < ARRAY_SIZE(nmap->entry); idx++) {
+		if (nmap->entry[idx].key) {
+			memcpy(next_key, nmap->entry[idx].key,
+			       offmap->map.key_size);
+			break;
+		}
+	}
+
+	mutex_unlock(&nmap->mutex);
+
+	if (idx == ARRAY_SIZE(nmap->entry))
+		return -ENOENT;
+	return 0;
+}
+
+static int
+nsim_map_lookup_elem(struct bpf_offloaded_map *offmap, void *key, void *value)
+{
+	struct nsim_bpf_bound_map *nmap = offmap->dev_priv;
+	int idx;
+
+	mutex_lock(&nmap->mutex);
+
+	idx = nsim_map_key_find(offmap, key);
+	if (idx >= 0)
+		memcpy(value, nmap->entry[idx].value, offmap->map.value_size);
+
+	mutex_unlock(&nmap->mutex);
+
+	return idx < 0 ? idx : 0;
+}
+
+static int
+nsim_map_update_elem(struct bpf_offloaded_map *offmap,
+		     void *key, void *value, u64 flags)
+{
+	struct nsim_bpf_bound_map *nmap = offmap->dev_priv;
+	int idx, err = 0;
+
+	mutex_lock(&nmap->mutex);
+
+	idx = nsim_map_key_find(offmap, key);
+	if (idx < 0 && flags == BPF_EXIST) {
+		err = idx;
+		goto exit_unlock;
+	}
+	if (idx >= 0 && flags == BPF_NOEXIST) {
+		err = -EEXIST;
+		goto exit_unlock;
+	}
+
+	if (idx < 0) {
+		for (idx = 0; idx < ARRAY_SIZE(nmap->entry); idx++)
+			if (!nmap->entry[idx].key)
+				break;
+		if (idx == ARRAY_SIZE(nmap->entry)) {
+			err = -E2BIG;
+			goto exit_unlock;
+		}
+
+		err = nsim_map_alloc_elem(offmap, idx);
+		if (err)
+			goto exit_unlock;
+	}
+
+	memcpy(nmap->entry[idx].key, key, offmap->map.key_size);
+	memcpy(nmap->entry[idx].value, value, offmap->map.value_size);
+exit_unlock:
+	mutex_unlock(&nmap->mutex);
+
+	return err;
+}
+
+static int nsim_map_delete_elem(struct bpf_offloaded_map *offmap, void *key)
+{
+	struct nsim_bpf_bound_map *nmap = offmap->dev_priv;
+	int idx;
+
+	if (offmap->map.map_type == BPF_MAP_TYPE_ARRAY)
+		return -EINVAL;
+
+	mutex_lock(&nmap->mutex);
+
+	idx = nsim_map_key_find(offmap, key);
+	if (idx >= 0) {
+		kfree(nmap->entry[idx].key);
+		kfree(nmap->entry[idx].value);
+		memset(&nmap->entry[idx], 0, sizeof(nmap->entry[idx]));
+	}
+
+	mutex_unlock(&nmap->mutex);
+
+	return idx < 0 ? idx : 0;
+}
+
+static const struct bpf_map_dev_ops nsim_bpf_map_ops = {
+	.map_get_next_key	= nsim_map_get_next_key,
+	.map_lookup_elem	= nsim_map_lookup_elem,
+	.map_update_elem	= nsim_map_update_elem,
+	.map_delete_elem	= nsim_map_delete_elem,
+};
+
+static int
+nsim_bpf_map_alloc(struct netdevsim *ns, struct bpf_offloaded_map *offmap)
+{
+	struct nsim_bpf_bound_map *nmap;
+	unsigned int i;
+	int err;
+
+	if (WARN_ON(offmap->map.map_type != BPF_MAP_TYPE_ARRAY &&
+		    offmap->map.map_type != BPF_MAP_TYPE_HASH))
+		return -EINVAL;
+	if (offmap->map.max_entries > NSIM_BPF_MAX_KEYS)
+		return -ENOMEM;
+	if (offmap->map.map_flags)
+		return -EINVAL;
+
+	nmap = kzalloc(sizeof(*nmap), GFP_USER);
+	if (!nmap)
+		return -ENOMEM;
+
+	offmap->dev_priv = nmap;
+	nmap->ns = ns;
+	nmap->map = offmap;
+	mutex_init(&nmap->mutex);
+
+	if (offmap->map.map_type == BPF_MAP_TYPE_ARRAY) {
+		for (i = 0; i < ARRAY_SIZE(nmap->entry); i++) {
+			u32 *key;
+
+			err = nsim_map_alloc_elem(offmap, i);
+			if (err)
+				goto err_free;
+			key = nmap->entry[i].key;
+			*key = i;
+		}
+	}
+
+	offmap->dev_ops = &nsim_bpf_map_ops;
+	list_add_tail(&nmap->l, &ns->bpf_bound_maps);
+
+	return 0;
+
+err_free:
+	while (--i) {
+		kfree(nmap->entry[i].key);
+		kfree(nmap->entry[i].value);
+	}
+	kfree(nmap);
+	return err;
+}
+
+static void nsim_bpf_map_free(struct bpf_offloaded_map *offmap)
+{
+	struct nsim_bpf_bound_map *nmap = offmap->dev_priv;
+	unsigned int i;
+
+	for (i = 0; i < ARRAY_SIZE(nmap->entry); i++) {
+		kfree(nmap->entry[i].key);
+		kfree(nmap->entry[i].value);
+	}
+	list_del_init(&nmap->l);
+	mutex_destroy(&nmap->mutex);
+	kfree(nmap);
+}
+
 int nsim_bpf(struct net_device *dev, struct netdev_bpf *bpf)
 {
 	struct netdevsim *ns = netdev_priv(dev);
@@ -328,6 +560,14 @@ int nsim_bpf(struct net_device *dev, struct netdev_bpf *bpf)
 			return err;
 
 		return nsim_xdp_set_prog(ns, bpf);
+	case BPF_OFFLOAD_MAP_ALLOC:
+		if (!ns->bpf_map_accept)
+			return -EOPNOTSUPP;
+
+		return nsim_bpf_map_alloc(ns, bpf->offmap);
+	case BPF_OFFLOAD_MAP_FREE:
+		nsim_bpf_map_free(bpf->offmap);
+		return 0;
 	default:
 		return -EINVAL;
 	}
@@ -336,6 +576,7 @@ int nsim_bpf(struct net_device *dev, struct netdev_bpf *bpf)
 int nsim_bpf_init(struct netdevsim *ns)
 {
 	INIT_LIST_HEAD(&ns->bpf_bound_progs);
+	INIT_LIST_HEAD(&ns->bpf_bound_maps);
 
 	debugfs_create_u32("bpf_offloaded_id", 0400, ns->ddir,
 			   &ns->bpf_offloaded_id);
@@ -362,12 +603,17 @@ int nsim_bpf_init(struct netdevsim *ns)
 	debugfs_create_bool("bpf_xdpoffload_accept", 0600, ns->ddir,
 			    &ns->bpf_xdpoffload_accept);
 
+	ns->bpf_map_accept = true;
+	debugfs_create_bool("bpf_map_accept", 0600, ns->ddir,
+			    &ns->bpf_map_accept);
+
 	return 0;
 }
 
 void nsim_bpf_uninit(struct netdevsim *ns)
 {
 	WARN_ON(!list_empty(&ns->bpf_bound_progs));
+	WARN_ON(!list_empty(&ns->bpf_bound_maps));
 	WARN_ON(ns->xdp_prog);
 	WARN_ON(ns->bpf_offloaded);
 }

drivers/net/netdevsim/netdevsim.h

@@ -61,6 +61,9 @@ struct netdevsim {
 	bool bpf_tc_non_bound_accept;
 	bool bpf_xdpdrv_accept;
 	bool bpf_xdpoffload_accept;
+
+	bool bpf_map_accept;
+	struct list_head bpf_bound_maps;
 };
 
 extern struct dentry *nsim_ddir;