Merge branch 'shared-cgroup-storage'

YiFei Zhu says:

====================
To access the storage in a CGROUP_STORAGE map, one uses
bpf_get_local_storage helper, which is extremely fast due to its
use of per-CPU variables. However, its whole code is built on
the assumption that one map can only be used by one program at any
time, and this prohibits any sharing of data between multiple
programs using these maps, eliminating a lot of use cases, such
as some per-cgroup configuration storage, written to by a
setsockopt program and read by a cg_sock_addr program.

Why not use other map types? The great part of CGROUP_STORAGE map
is that it is isolated by different cgroups its attached to. When
one program uses bpf_get_local_storage, even on the same map, it
gets different storages if it were run as a result of attaching
to different cgroups. The kernel manages the storages, simplifying
BPF program or userspace. In theory, one could probably use other
maps like array or hash to do the same thing, but it would be a
major overhead / complexity. Userspace needs to know when a cgroup
is being freed in order to free up a space in the replacement map.

This patch set introduces a significant change to the semantics of
CGROUP_STORAGE map type. Instead of each storage being tied to one
single attachment, it is shared across different attachments to
the same cgroup, and persists until either the map or the cgroup
attached to is being freed.

User may use u64 as the key to the map, and the result would be
that the attach type become ignored during key comparison, and
programs of different attach types will share the same storage if
the cgroups they are attached to are the same.

How could this break existing users?
* Users that uses detach & reattach / program replacement as a
  shortcut to zeroing the storage. Since we need sharing between
  programs, we cannot zero the storage. Users that expect this
  behavior should either attach a program with a new map, or
  explicitly zero the map with a syscall.
This case is dependent on undocumented implementation details,
so the impact should be very minimal.

Patch 1 introduces a test on the old expected behavior of the map
type.

Patch 2 introduces a test showing how two programs cannot share
one such map.

Patch 3 implements the change of semantics to the map.

Patch 4 amends the new test such that it yields the behavior we
expect from the change.

Patch 5 documents the map type.

Changes since RFC:
* Clarify commit message in patch 3 such that it says the lifetime
  of the storage is ended at the freeing of the cgroup_bpf, rather
  than the cgroup itself.
* Restored an -ENOMEM check in __cgroup_bpf_attach.
* Update selftests for recent change in network_helpers API.

Changes since v1:
* s/CHECK_FAIL/CHECK/
* s/bpf_prog_attach/bpf_program__attach_cgroup/
* Moved test__start_subtest to test_cg_storage_multi.
* Removed some redundant CHECK_FAIL where they are already CHECK-ed.

Changes since v2:
* Lock cgroup_mutex during map_free.
* Publish new storages only if attach is successful, by tracking
  exactly which storages are reused in an array of bools.
* Mention bpftool map dump showing a value of zero for attach_type
  in patch 3 commit message.

Changes since v3:
* Use a much simpler lookup and allocate-if-not-exist from the fact
  that cgroup_mutex is locked during attach.
* Removed an unnecessary spinlock hold.

Changes since v4:
* Changed semantics so that if the key type is struct
  bpf_cgroup_storage_key the map retains isolation between different
  attach types. Sharing between different attach types only occur
  when key type is u64.
* Adapted tests and docs for the above change.

Changes since v5:
* Removed redundant NULL check before bpf_link__destroy.
* Free BPF object explicitly, after asserting that object failed to
  load, in the event that the object did not fail to load.
* Rename variable in bpf_cgroup_storage_key_cmp for clarity.
* Added a lot of information to Documentation, more or less copied
  from what Martin KaFai Lau wrote.
====================

Acked-by: Martin KaFai Lau <kafai@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 117 insertions, 99 deletions

diff --git a/kernel/bpf/local_storage.c b/kernel/bpf/local_storage.c
index 51bd5a8cb01b..3b2c70197d78 100644
--- a/kernel/bpf/local_storage.c
+++ b/kernel/bpf/local_storage.c
@@ -9,6 +9,8 @@
 #include <linux/slab.h>
 #include <uapi/linux/btf.h>
 
+#include "../cgroup/cgroup-internal.h"
+
 DEFINE_PER_CPU(struct bpf_cgroup_storage*, bpf_cgroup_storage[MAX_BPF_CGROUP_STORAGE_TYPE]);
 
 #ifdef CONFIG_CGROUP_BPF
@@ -20,7 +22,6 @@ struct bpf_cgroup_storage_map {
 	struct bpf_map map;
 
 	spinlock_t lock;
-	struct bpf_prog_aux *aux;
 	struct rb_root root;
 	struct list_head list;
 };
@@ -30,24 +31,41 @@ static struct bpf_cgroup_storage_map *map_to_storage(struct bpf_map *map)
 	return container_of(map, struct bpf_cgroup_storage_map, map);
 }
 
-static int bpf_cgroup_storage_key_cmp(
-	const struct bpf_cgroup_storage_key *key1,
-	const struct bpf_cgroup_storage_key *key2)
+static bool attach_type_isolated(const struct bpf_map *map)
 {
-	if (key1->cgroup_inode_id < key2->cgroup_inode_id)
-		return -1;
-	else if (key1->cgroup_inode_id > key2->cgroup_inode_id)
-		return 1;
-	else if (key1->attach_type < key2->attach_type)
-		return -1;
-	else if (key1->attach_type > key2->attach_type)
-		return 1;
+	return map->key_size == sizeof(struct bpf_cgroup_storage_key);
+}
+
+static int bpf_cgroup_storage_key_cmp(const struct bpf_cgroup_storage_map *map,
+				      const void *_key1, const void *_key2)
+{
+	if (attach_type_isolated(&map->map)) {
+		const struct bpf_cgroup_storage_key *key1 = _key1;
+		const struct bpf_cgroup_storage_key *key2 = _key2;
+
+		if (key1->cgroup_inode_id < key2->cgroup_inode_id)
+			return -1;
+		else if (key1->cgroup_inode_id > key2->cgroup_inode_id)
+			return 1;
+		else if (key1->attach_type < key2->attach_type)
+			return -1;
+		else if (key1->attach_type > key2->attach_type)
+			return 1;
+	} else {
+		const __u64 *cgroup_inode_id1 = _key1;
+		const __u64 *cgroup_inode_id2 = _key2;
+
+		if (*cgroup_inode_id1 < *cgroup_inode_id2)
+			return -1;
+		else if (*cgroup_inode_id1 > *cgroup_inode_id2)
+			return 1;
+	}
 	return 0;
 }
 
-static struct bpf_cgroup_storage *cgroup_storage_lookup(
-	struct bpf_cgroup_storage_map *map, struct bpf_cgroup_storage_key *key,
-	bool locked)
+struct bpf_cgroup_storage *
+cgroup_storage_lookup(struct bpf_cgroup_storage_map *map,
+		      void *key, bool locked)
 {
 	struct rb_root *root = &map->root;
 	struct rb_node *node;
@@ -61,7 +79,7 @@ static struct bpf_cgroup_storage *cgroup_storage_lookup(
 
 		storage = container_of(node, struct bpf_cgroup_storage, node);
 
-		switch (bpf_cgroup_storage_key_cmp(key, &storage->key)) {
+		switch (bpf_cgroup_storage_key_cmp(map, key, &storage->key)) {
 		case -1:
 			node = node->rb_left;
 			break;
@@ -93,7 +111,7 @@ static int cgroup_storage_insert(struct bpf_cgroup_storage_map *map,
 		this = container_of(*new, struct bpf_cgroup_storage, node);
 
 		parent = *new;
-		switch (bpf_cgroup_storage_key_cmp(&storage->key, &this->key)) {
+		switch (bpf_cgroup_storage_key_cmp(map, &storage->key, &this->key)) {
 		case -1:
 			new = &((*new)->rb_left);
 			break;
@@ -111,10 +129,9 @@ static int cgroup_storage_insert(struct bpf_cgroup_storage_map *map,
 	return 0;
 }
 
-static void *cgroup_storage_lookup_elem(struct bpf_map *_map, void *_key)
+static void *cgroup_storage_lookup_elem(struct bpf_map *_map, void *key)
 {
 	struct bpf_cgroup_storage_map *map = map_to_storage(_map);
-	struct bpf_cgroup_storage_key *key = _key;
 	struct bpf_cgroup_storage *storage;
 
 	storage = cgroup_storage_lookup(map, key, false);
@@ -124,17 +141,13 @@ static void *cgroup_storage_lookup_elem(struct bpf_map *_map, void *_key)
 	return &READ_ONCE(storage->buf)->data[0];
 }
 
-static int cgroup_storage_update_elem(struct bpf_map *map, void *_key,
+static int cgroup_storage_update_elem(struct bpf_map *map, void *key,
 				      void *value, u64 flags)
 {
-	struct bpf_cgroup_storage_key *key = _key;
 	struct bpf_cgroup_storage *storage;
 	struct bpf_storage_buffer *new;
 
-	if (unlikely(flags & ~(BPF_F_LOCK | BPF_EXIST | BPF_NOEXIST)))
-		return -EINVAL;
-
-	if (unlikely(flags & BPF_NOEXIST))
+	if (unlikely(flags & ~(BPF_F_LOCK | BPF_EXIST)))
 		return -EINVAL;
 
 	if (unlikely((flags & BPF_F_LOCK) &&
@@ -167,11 +180,10 @@ static int cgroup_storage_update_elem(struct bpf_map *map, void *_key,
 	return 0;
 }
 
-int bpf_percpu_cgroup_storage_copy(struct bpf_map *_map, void *_key,
+int bpf_percpu_cgroup_storage_copy(struct bpf_map *_map, void *key,
 				   void *value)
 {
 	struct bpf_cgroup_storage_map *map = map_to_storage(_map);
-	struct bpf_cgroup_storage_key *key = _key;
 	struct bpf_cgroup_storage *storage;
 	int cpu, off = 0;
 	u32 size;
@@ -197,11 +209,10 @@ int bpf_percpu_cgroup_storage_copy(struct bpf_map *_map, void *_key,
 	return 0;
 }
 
-int bpf_percpu_cgroup_storage_update(struct bpf_map *_map, void *_key,
+int bpf_percpu_cgroup_storage_update(struct bpf_map *_map, void *key,
 				     void *value, u64 map_flags)
 {
 	struct bpf_cgroup_storage_map *map = map_to_storage(_map);
-	struct bpf_cgroup_storage_key *key = _key;
 	struct bpf_cgroup_storage *storage;
 	int cpu, off = 0;
 	u32 size;
@@ -232,12 +243,10 @@ int bpf_percpu_cgroup_storage_update(struct bpf_map *_map, void *_key,
 	return 0;
 }
 
-static int cgroup_storage_get_next_key(struct bpf_map *_map, void *_key,
+static int cgroup_storage_get_next_key(struct bpf_map *_map, void *key,
 				       void *_next_key)
 {
 	struct bpf_cgroup_storage_map *map = map_to_storage(_map);
-	struct bpf_cgroup_storage_key *key = _key;
-	struct bpf_cgroup_storage_key *next = _next_key;
 	struct bpf_cgroup_storage *storage;
 
 	spin_lock_bh(&map->lock);
@@ -250,17 +259,23 @@ static int cgroup_storage_get_next_key(struct bpf_map *_map, void *_key,
 		if (!storage)
 			goto enoent;
 
-		storage = list_next_entry(storage, list);
+		storage = list_next_entry(storage, list_map);
 		if (!storage)
 			goto enoent;
 	} else {
 		storage = list_first_entry(&map->list,
-					 struct bpf_cgroup_storage, list);
+					 struct bpf_cgroup_storage, list_map);
 	}
 
 	spin_unlock_bh(&map->lock);
-	next->attach_type = storage->key.attach_type;
-	next->cgroup_inode_id = storage->key.cgroup_inode_id;
+
+	if (attach_type_isolated(&map->map)) {
+		struct bpf_cgroup_storage_key *next = _next_key;
+		*next = storage->key;
+	} else {
+		__u64 *next = _next_key;
+		*next = storage->key.cgroup_inode_id;
+	}
 	return 0;
 
 enoent:
@@ -275,7 +290,8 @@ static struct bpf_map *cgroup_storage_map_alloc(union bpf_attr *attr)
 	struct bpf_map_memory mem;
 	int ret;
 
-	if (attr->key_size != sizeof(struct bpf_cgroup_storage_key))
+	if (attr->key_size != sizeof(struct bpf_cgroup_storage_key) &&
+	    attr->key_size != sizeof(__u64))
 		return ERR_PTR(-EINVAL);
 
 	if (attr->value_size == 0)
@@ -318,6 +334,17 @@ static struct bpf_map *cgroup_storage_map_alloc(union bpf_attr *attr)
 static void cgroup_storage_map_free(struct bpf_map *_map)
 {
 	struct bpf_cgroup_storage_map *map = map_to_storage(_map);
+	struct list_head *storages = &map->list;
+	struct bpf_cgroup_storage *storage, *stmp;
+
+	mutex_lock(&cgroup_mutex);
+
+	list_for_each_entry_safe(storage, stmp, storages, list_map) {
+		bpf_cgroup_storage_unlink(storage);
+		bpf_cgroup_storage_free(storage);
+	}
+
+	mutex_unlock(&cgroup_mutex);
 
 	WARN_ON(!RB_EMPTY_ROOT(&map->root));
 	WARN_ON(!list_empty(&map->list));
@@ -335,49 +362,63 @@ static int cgroup_storage_check_btf(const struct bpf_map *map,
 				    const struct btf_type *key_type,
 				    const struct btf_type *value_type)
 {
-	struct btf_member *m;
-	u32 offset, size;
-
-	/* Key is expected to be of struct bpf_cgroup_storage_key type,
-	 * which is:
-	 * struct bpf_cgroup_storage_key {
-	 *	__u64	cgroup_inode_id;
-	 *	__u32	attach_type;
-	 * };
-	 */
+	if (attach_type_isolated(map)) {
+		struct btf_member *m;
+		u32 offset, size;
+
+		/* Key is expected to be of struct bpf_cgroup_storage_key type,
+		 * which is:
+		 * struct bpf_cgroup_storage_key {
+		 *	__u64	cgroup_inode_id;
+		 *	__u32	attach_type;
+		 * };
+		 */
+
+		/*
+		 * Key_type must be a structure with two fields.
+		 */
+		if (BTF_INFO_KIND(key_type->info) != BTF_KIND_STRUCT ||
+		    BTF_INFO_VLEN(key_type->info) != 2)
+			return -EINVAL;
+
+		/*
+		 * The first field must be a 64 bit integer at 0 offset.
+		 */
+		m = (struct btf_member *)(key_type + 1);
+		size = sizeof_field(struct bpf_cgroup_storage_key, cgroup_inode_id);
+		if (!btf_member_is_reg_int(btf, key_type, m, 0, size))
+			return -EINVAL;
+
+		/*
+		 * The second field must be a 32 bit integer at 64 bit offset.
+		 */
+		m++;
+		offset = offsetof(struct bpf_cgroup_storage_key, attach_type);
+		size = sizeof_field(struct bpf_cgroup_storage_key, attach_type);
+		if (!btf_member_is_reg_int(btf, key_type, m, offset, size))
+			return -EINVAL;
+	} else {
+		u32 int_data;
 
-	/*
-	 * Key_type must be a structure with two fields.
-	 */
-	if (BTF_INFO_KIND(key_type->info) != BTF_KIND_STRUCT ||
-	    BTF_INFO_VLEN(key_type->info) != 2)
-		return -EINVAL;
+		/*
+		 * Key is expected to be u64, which stores the cgroup_inode_id
+		 */
 
-	/*
-	 * The first field must be a 64 bit integer at 0 offset.
-	 */
-	m = (struct btf_member *)(key_type + 1);
-	size = sizeof_field(struct bpf_cgroup_storage_key, cgroup_inode_id);
-	if (!btf_member_is_reg_int(btf, key_type, m, 0, size))
-		return -EINVAL;
+		if (BTF_INFO_KIND(key_type->info) != BTF_KIND_INT)
+			return -EINVAL;
 
-	/*
-	 * The second field must be a 32 bit integer at 64 bit offset.
-	 */
-	m++;
-	offset = offsetof(struct bpf_cgroup_storage_key, attach_type);
-	size = sizeof_field(struct bpf_cgroup_storage_key, attach_type);
-	if (!btf_member_is_reg_int(btf, key_type, m, offset, size))
-		return -EINVAL;
+		int_data = *(u32 *)(key_type + 1);
+		if (BTF_INT_BITS(int_data) != 64 || BTF_INT_OFFSET(int_data))
+			return -EINVAL;
+	}
 
 	return 0;
 }
 
-static void cgroup_storage_seq_show_elem(struct bpf_map *map, void *_key,
+static void cgroup_storage_seq_show_elem(struct bpf_map *map, void *key,
 					 struct seq_file *m)
 {
 	enum bpf_cgroup_storage_type stype = cgroup_storage_type(map);
-	struct bpf_cgroup_storage_key *key = _key;
 	struct bpf_cgroup_storage *storage;
 	int cpu;
 
@@ -426,38 +467,13 @@ const struct bpf_map_ops cgroup_storage_map_ops = {
 int bpf_cgroup_storage_assign(struct bpf_prog_aux *aux, struct bpf_map *_map)
 {
 	enum bpf_cgroup_storage_type stype = cgroup_storage_type(_map);
-	struct bpf_cgroup_storage_map *map = map_to_storage(_map);
-	int ret = -EBUSY;
-
-	spin_lock_bh(&map->lock);
 
-	if (map->aux && map->aux != aux)
-		goto unlock;
 	if (aux->cgroup_storage[stype] &&
 	    aux->cgroup_storage[stype] != _map)
-		goto unlock;
+		return -EBUSY;
 
-	map->aux = aux;
 	aux->cgroup_storage[stype] = _map;
-	ret = 0;
-unlock:
-	spin_unlock_bh(&map->lock);
-
-	return ret;
-}
-
-void bpf_cgroup_storage_release(struct bpf_prog_aux *aux, struct bpf_map *_map)
-{
-	enum bpf_cgroup_storage_type stype = cgroup_storage_type(_map);
-	struct bpf_cgroup_storage_map *map = map_to_storage(_map);
-
-	spin_lock_bh(&map->lock);
-	if (map->aux == aux) {
-		WARN_ON(aux->cgroup_storage[stype] != _map);
-		map->aux = NULL;
-		aux->cgroup_storage[stype] = NULL;
-	}
-	spin_unlock_bh(&map->lock);
+	return 0;
 }
 
 static size_t bpf_cgroup_storage_calculate_size(struct bpf_map *map, u32 *pages)
@@ -578,7 +594,8 @@ void bpf_cgroup_storage_link(struct bpf_cgroup_storage *storage,
 
 	spin_lock_bh(&map->lock);
 	WARN_ON(cgroup_storage_insert(map, storage));
-	list_add(&storage->list, &map->list);
+	list_add(&storage->list_map, &map->list);
+	list_add(&storage->list_cg, &cgroup->bpf.storages);
 	spin_unlock_bh(&map->lock);
 }
 
@@ -596,7 +613,8 @@ void bpf_cgroup_storage_unlink(struct bpf_cgroup_storage *storage)
 	root = &map->root;
 	rb_erase(&storage->node, root);
 
-	list_del(&storage->list);
+	list_del(&storage->list_map);
+	list_del(&storage->list_cg);
 	spin_unlock_bh(&map->lock);
 }