From: Andrii Nakryiko <andrii@kernel.org>
Date: Thu, 12 May 2022 15:07:12 -0700
Subject: libbpf: Add safer high-level wrappers for map operations
Patch-mainline: v5.19-rc1
Git-commit: 737d0646a83cdc65c070a9de61a1ef106cca5ff1
References: jsc#PED-1377
Add high-level API wrappers for most common and typical BPF map
operations that works directly on instances of struct bpf_map * (so
you don't have to call bpf_map__fd()) and validate key/value size
expectations.
These helpers require users to specify key (and value, where
appropriate) sizes when performing lookup/update/delete/etc. This forces
user to actually think and validate (for themselves) those. This is
a good thing as user is expected by kernel to implicitly provide correct
key/value buffer sizes and kernel will just read/write necessary amount
of data. If it so happens that user doesn't set up buffers correctly
(which bit people for per-CPU maps especially) kernel either randomly
overwrites stack data or return -EFAULT, depending on user's luck and
circumstances. These high-level APIs are meant to prevent such
unpleasant and hard to debug bugs.
This patch also adds bpf_map_delete_elem_flags() low-level API and
requires passing flags to bpf_map__delete_elem() API for consistency
across all similar APIs, even though currently kernel doesn't expect
any extra flags for BPF_MAP_DELETE_ELEM operation.
List of map operations that get these high-level APIs:
- bpf_map_lookup_elem;
- bpf_map_update_elem;
- bpf_map_delete_elem;
- bpf_map_lookup_and_delete_elem;
- bpf_map_get_next_key.
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20220512220713.2617964-1-andrii@kernel.org
Acked-by: Shung-Hsi Yu <shung-hsi.yu@suse.com>
---
tools/lib/bpf/bpf.c | 14 ++++++
tools/lib/bpf/bpf.h | 1
tools/lib/bpf/libbpf.c | 104 +++++++++++++++++++++++++++++++++++++++++++++++
tools/lib/bpf/libbpf.h | 104 +++++++++++++++++++++++++++++++++++++++++++++++
tools/lib/bpf/libbpf.map | 6 ++
5 files changed, 229 insertions(+)
--- a/tools/lib/bpf/bpf.c
+++ b/tools/lib/bpf/bpf.c
@@ -639,6 +639,20 @@ int bpf_map_delete_elem(int fd, const vo
return libbpf_err_errno(ret);
}
+int bpf_map_delete_elem_flags(int fd, const void *key, __u64 flags)
+{
+ union bpf_attr attr;
+ int ret;
+
+ memset(&attr, 0, sizeof(attr));
+ attr.map_fd = fd;
+ attr.key = ptr_to_u64(key);
+ attr.flags = flags;
+
+ ret = sys_bpf(BPF_MAP_DELETE_ELEM, &attr, sizeof(attr));
+ return libbpf_err_errno(ret);
+}
+
int bpf_map_get_next_key(int fd, const void *key, void *next_key)
{
union bpf_attr attr;
--- a/tools/lib/bpf/bpf.h
+++ b/tools/lib/bpf/bpf.h
@@ -244,6 +244,7 @@ LIBBPF_API int bpf_map_lookup_and_delete
LIBBPF_API int bpf_map_lookup_and_delete_elem_flags(int fd, const void *key,
void *value, __u64 flags);
LIBBPF_API int bpf_map_delete_elem(int fd, const void *key);
+LIBBPF_API int bpf_map_delete_elem_flags(int fd, const void *key, __u64 flags);
LIBBPF_API int bpf_map_get_next_key(int fd, const void *key, void *next_key);
LIBBPF_API int bpf_map_freeze(int fd);
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -9949,6 +9949,110 @@ bpf_object__find_map_by_offset(struct bp
return libbpf_err_ptr(-ENOTSUP);
}
+static int validate_map_op(const struct bpf_map *map, size_t key_sz,
+ size_t value_sz, bool check_value_sz)
+{
+ if (map->fd <= 0)
+ return -ENOENT;
+
+ if (map->def.key_size != key_sz) {
+ pr_warn("map '%s': unexpected key size %zu provided, expected %u\n",
+ map->name, key_sz, map->def.key_size);
+ return -EINVAL;
+ }
+
+ if (!check_value_sz)
+ return 0;
+
+ switch (map->def.type) {
+ case BPF_MAP_TYPE_PERCPU_ARRAY:
+ case BPF_MAP_TYPE_PERCPU_HASH:
+ case BPF_MAP_TYPE_LRU_PERCPU_HASH:
+ case BPF_MAP_TYPE_PERCPU_CGROUP_STORAGE: {
+ int num_cpu = libbpf_num_possible_cpus();
+ size_t elem_sz = roundup(map->def.value_size, 8);
+
+ if (value_sz != num_cpu * elem_sz) {
+ pr_warn("map '%s': unexpected value size %zu provided for per-CPU map, expected %d * %zu = %zd\n",
+ map->name, value_sz, num_cpu, elem_sz, num_cpu * elem_sz);
+ return -EINVAL;
+ }
+ break;
+ }
+ default:
+ if (map->def.value_size != value_sz) {
+ pr_warn("map '%s': unexpected value size %zu provided, expected %u\n",
+ map->name, value_sz, map->def.value_size);
+ return -EINVAL;
+ }
+ break;
+ }
+ return 0;
+}
+
+int bpf_map__lookup_elem(const struct bpf_map *map,
+ const void *key, size_t key_sz,
+ void *value, size_t value_sz, __u64 flags)
+{
+ int err;
+
+ err = validate_map_op(map, key_sz, value_sz, true);
+ if (err)
+ return libbpf_err(err);
+
+ return bpf_map_lookup_elem_flags(map->fd, key, value, flags);
+}
+
+int bpf_map__update_elem(const struct bpf_map *map,
+ const void *key, size_t key_sz,
+ const void *value, size_t value_sz, __u64 flags)
+{
+ int err;
+
+ err = validate_map_op(map, key_sz, value_sz, true);
+ if (err)
+ return libbpf_err(err);
+
+ return bpf_map_update_elem(map->fd, key, value, flags);
+}
+
+int bpf_map__delete_elem(const struct bpf_map *map,
+ const void *key, size_t key_sz, __u64 flags)
+{
+ int err;
+
+ err = validate_map_op(map, key_sz, 0, false /* check_value_sz */);
+ if (err)
+ return libbpf_err(err);
+
+ return bpf_map_delete_elem_flags(map->fd, key, flags);
+}
+
+int bpf_map__lookup_and_delete_elem(const struct bpf_map *map,
+ const void *key, size_t key_sz,
+ void *value, size_t value_sz, __u64 flags)
+{
+ int err;
+
+ err = validate_map_op(map, key_sz, value_sz, true);
+ if (err)
+ return libbpf_err(err);
+
+ return bpf_map_lookup_and_delete_elem_flags(map->fd, key, value, flags);
+}
+
+int bpf_map__get_next_key(const struct bpf_map *map,
+ const void *cur_key, void *next_key, size_t key_sz)
+{
+ int err;
+
+ err = validate_map_op(map, key_sz, 0, false /* check_value_sz */);
+ if (err)
+ return libbpf_err(err);
+
+ return bpf_map_get_next_key(map->fd, cur_key, next_key);
+}
+
long libbpf_get_error(const void *ptr)
{
if (!IS_ERR_OR_NULL(ptr))
--- a/tools/lib/bpf/libbpf.h
+++ b/tools/lib/bpf/libbpf.h
@@ -991,6 +991,110 @@ LIBBPF_API int bpf_map__set_inner_map_fd
LIBBPF_API struct bpf_map *bpf_map__inner_map(struct bpf_map *map);
/**
+ * @brief **bpf_map__lookup_elem()** allows to lookup BPF map value
+ * corresponding to provided key.
+ * @param map BPF map to lookup element in
+ * @param key pointer to memory containing bytes of the key used for lookup
+ * @param key_sz size in bytes of key data, needs to match BPF map definition's **key_size**
+ * @param value pointer to memory in which looked up value will be stored
+ * @param value_sz size in byte of value data memory; it has to match BPF map
+ * definition's **value_size**. For per-CPU BPF maps value size has to be
+ * a product of BPF map value size and number of possible CPUs in the system
+ * (could be fetched with **libbpf_num_possible_cpus()**). Note also that for
+ * per-CPU values value size has to be aligned up to closest 8 bytes for
+ * alignment reasons, so expected size is: `round_up(value_size, 8)
+ * * libbpf_num_possible_cpus()`.
+ * @flags extra flags passed to kernel for this operation
+ * @return 0, on success; negative error, otherwise
+ *
+ * **bpf_map__lookup_elem()** is high-level equivalent of
+ * **bpf_map_lookup_elem()** API with added check for key and value size.
+ */
+LIBBPF_API int bpf_map__lookup_elem(const struct bpf_map *map,
+ const void *key, size_t key_sz,
+ void *value, size_t value_sz, __u64 flags);
+
+/**
+ * @brief **bpf_map__update_elem()** allows to insert or update value in BPF
+ * map that corresponds to provided key.
+ * @param map BPF map to insert to or update element in
+ * @param key pointer to memory containing bytes of the key
+ * @param key_sz size in bytes of key data, needs to match BPF map definition's **key_size**
+ * @param value pointer to memory containing bytes of the value
+ * @param value_sz size in byte of value data memory; it has to match BPF map
+ * definition's **value_size**. For per-CPU BPF maps value size has to be
+ * a product of BPF map value size and number of possible CPUs in the system
+ * (could be fetched with **libbpf_num_possible_cpus()**). Note also that for
+ * per-CPU values value size has to be aligned up to closest 8 bytes for
+ * alignment reasons, so expected size is: `round_up(value_size, 8)
+ * * libbpf_num_possible_cpus()`.
+ * @flags extra flags passed to kernel for this operation
+ * @return 0, on success; negative error, otherwise
+ *
+ * **bpf_map__update_elem()** is high-level equivalent of
+ * **bpf_map_update_elem()** API with added check for key and value size.
+ */
+LIBBPF_API int bpf_map__update_elem(const struct bpf_map *map,
+ const void *key, size_t key_sz,
+ const void *value, size_t value_sz, __u64 flags);
+
+/**
+ * @brief **bpf_map__delete_elem()** allows to delete element in BPF map that
+ * corresponds to provided key.
+ * @param map BPF map to delete element from
+ * @param key pointer to memory containing bytes of the key
+ * @param key_sz size in bytes of key data, needs to match BPF map definition's **key_size**
+ * @flags extra flags passed to kernel for this operation
+ * @return 0, on success; negative error, otherwise
+ *
+ * **bpf_map__delete_elem()** is high-level equivalent of
+ * **bpf_map_delete_elem()** API with added check for key size.
+ */
+LIBBPF_API int bpf_map__delete_elem(const struct bpf_map *map,
+ const void *key, size_t key_sz, __u64 flags);
+
+/**
+ * @brief **bpf_map__lookup_and_delete_elem()** allows to lookup BPF map value
+ * corresponding to provided key and atomically delete it afterwards.
+ * @param map BPF map to lookup element in
+ * @param key pointer to memory containing bytes of the key used for lookup
+ * @param key_sz size in bytes of key data, needs to match BPF map definition's **key_size**
+ * @param value pointer to memory in which looked up value will be stored
+ * @param value_sz size in byte of value data memory; it has to match BPF map
+ * definition's **value_size**. For per-CPU BPF maps value size has to be
+ * a product of BPF map value size and number of possible CPUs in the system
+ * (could be fetched with **libbpf_num_possible_cpus()**). Note also that for
+ * per-CPU values value size has to be aligned up to closest 8 bytes for
+ * alignment reasons, so expected size is: `round_up(value_size, 8)
+ * * libbpf_num_possible_cpus()`.
+ * @flags extra flags passed to kernel for this operation
+ * @return 0, on success; negative error, otherwise
+ *
+ * **bpf_map__lookup_and_delete_elem()** is high-level equivalent of
+ * **bpf_map_lookup_and_delete_elem()** API with added check for key and value size.
+ */
+LIBBPF_API int bpf_map__lookup_and_delete_elem(const struct bpf_map *map,
+ const void *key, size_t key_sz,
+ void *value, size_t value_sz, __u64 flags);
+
+/**
+ * @brief **bpf_map__get_next_key()** allows to iterate BPF map keys by
+ * fetching next key that follows current key.
+ * @param map BPF map to fetch next key from
+ * @param cur_key pointer to memory containing bytes of current key or NULL to
+ * fetch the first key
+ * @param next_key pointer to memory to write next key into
+ * @param key_sz size in bytes of key data, needs to match BPF map definition's **key_size**
+ * @return 0, on success; -ENOENT if **cur_key** is the last key in BPF map;
+ * negative error, otherwise
+ *
+ * **bpf_map__get_next_key()** is high-level equivalent of
+ * **bpf_map_get_next_key()** API with added check for key size.
+ */
+LIBBPF_API int bpf_map__get_next_key(const struct bpf_map *map,
+ const void *cur_key, void *next_key, size_t key_sz);
+
+/**
* @brief **libbpf_get_error()** extracts the error code from the passed
* pointer
* @param ptr pointer returned from libbpf API function
--- a/tools/lib/bpf/libbpf.map
+++ b/tools/lib/bpf/libbpf.map
@@ -443,7 +443,13 @@ LIBBPF_0.7.0 {
LIBBPF_0.8.0 {
global:
bpf_map__autocreate;
+ bpf_map__get_next_key;
+ bpf_map__delete_elem;
+ bpf_map__lookup_and_delete_elem;
+ bpf_map__lookup_elem;
bpf_map__set_autocreate;
+ bpf_map__update_elem;
+ bpf_map_delete_elem_flags;
bpf_object__destroy_subskeleton;
bpf_object__open_subskeleton;
bpf_program__attach_kprobe_multi_opts;