bpf: btf: Introduce BTF ID

This patch gives an ID to each loaded BTF.  The ID is allocated by
the idr like the existing prog-id and map-id.

The bpf_put(map->btf) is moved to __bpf_map_put() so that the
userspace can stop seeing the BTF ID ASAP when the last BTF
refcnt is gone.

It also makes BTF accessible from userspace through the
1. new BPF_BTF_GET_FD_BY_ID command.  It is limited to CAP_SYS_ADMIN
   which is inline with the BPF_BTF_LOAD cmd and the existing
   BPF_[MAP|PROG]_GET_FD_BY_ID cmd.
2. new btf_id (and btf_key_id + btf_value_id) in "struct bpf_map_info"

Once the BTF ID handler is accessible from userspace, freeing a BTF
object has to go through a rcu period.  The BPF_BTF_GET_FD_BY_ID cmd
can then be done under a rcu_read_lock() instead of taking
spin_lock.
[Note: A similar rcu usage can be done to the existing
       bpf_prog_get_fd_by_id() in a follow up patch]

When processing the BPF_BTF_GET_FD_BY_ID cmd,
refcount_inc_not_zero() is needed because the BTF object
could be already in the rcu dead row .  btf_get() is
removed since its usage is currently limited to btf.c
alone.  refcount_inc() is used directly instead.

Signed-off-by: Martin KaFai Lau <kafai@fb.com>
Acked-by: Alexei Starovoitov <ast@fb.com>
Acked-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
This commit is contained in:
Martin KaFai Lau 2018-05-04 14:49:51 -07:00 committed by Daniel Borkmann
parent 82e9697250
commit 78958fca7e
4 changed files with 128 additions and 11 deletions

View File

@ -44,5 +44,7 @@ const struct btf_type *btf_type_id_size(const struct btf *btf,
u32 *ret_size);
void btf_type_seq_show(const struct btf *btf, u32 type_id, void *obj,
struct seq_file *m);
int btf_get_fd_by_id(u32 id);
u32 btf_id(const struct btf *btf);
#endif

View File

@ -96,6 +96,7 @@ enum bpf_cmd {
BPF_PROG_QUERY,
BPF_RAW_TRACEPOINT_OPEN,
BPF_BTF_LOAD,
BPF_BTF_GET_FD_BY_ID,
};
enum bpf_map_type {
@ -344,6 +345,7 @@ union bpf_attr {
__u32 start_id;
__u32 prog_id;
__u32 map_id;
__u32 btf_id;
};
__u32 next_id;
__u32 open_flags;
@ -2130,6 +2132,9 @@ struct bpf_map_info {
__u32 ifindex;
__u64 netns_dev;
__u64 netns_ino;
__u32 btf_id;
__u32 btf_key_id;
__u32 btf_value_id;
} __attribute__((aligned(8)));
/* User bpf_sock_addr struct to access socket fields and sockaddr struct passed

View File

@ -11,6 +11,7 @@
#include <linux/file.h>
#include <linux/uaccess.h>
#include <linux/kernel.h>
#include <linux/idr.h>
#include <linux/bpf_verifier.h>
#include <linux/btf.h>
@ -179,6 +180,9 @@
i < btf_type_vlen(struct_type); \
i++, member++)
static DEFINE_IDR(btf_idr);
static DEFINE_SPINLOCK(btf_idr_lock);
struct btf {
union {
struct btf_header *hdr;
@ -193,6 +197,8 @@ struct btf {
u32 types_size;
u32 data_size;
refcount_t refcnt;
u32 id;
struct rcu_head rcu;
};
enum verifier_phase {
@ -598,6 +604,42 @@ static int btf_add_type(struct btf_verifier_env *env, struct btf_type *t)
return 0;
}
static int btf_alloc_id(struct btf *btf)
{
int id;
idr_preload(GFP_KERNEL);
spin_lock_bh(&btf_idr_lock);
id = idr_alloc_cyclic(&btf_idr, btf, 1, INT_MAX, GFP_ATOMIC);
if (id > 0)
btf->id = id;
spin_unlock_bh(&btf_idr_lock);
idr_preload_end();
if (WARN_ON_ONCE(!id))
return -ENOSPC;
return id > 0 ? 0 : id;
}
static void btf_free_id(struct btf *btf)
{
unsigned long flags;
/*
* In map-in-map, calling map_delete_elem() on outer
* map will call bpf_map_put on the inner map.
* It will then eventually call btf_free_id()
* on the inner map. Some of the map_delete_elem()
* implementation may have irq disabled, so
* we need to use the _irqsave() version instead
* of the _bh() version.
*/
spin_lock_irqsave(&btf_idr_lock, flags);
idr_remove(&btf_idr, btf->id);
spin_unlock_irqrestore(&btf_idr_lock, flags);
}
static void btf_free(struct btf *btf)
{
kvfree(btf->types);
@ -607,15 +649,19 @@ static void btf_free(struct btf *btf)
kfree(btf);
}
static void btf_get(struct btf *btf)
static void btf_free_rcu(struct rcu_head *rcu)
{
refcount_inc(&btf->refcnt);
struct btf *btf = container_of(rcu, struct btf, rcu);
btf_free(btf);
}
void btf_put(struct btf *btf)
{
if (btf && refcount_dec_and_test(&btf->refcnt))
btf_free(btf);
if (btf && refcount_dec_and_test(&btf->refcnt)) {
btf_free_id(btf);
call_rcu(&btf->rcu, btf_free_rcu);
}
}
static int env_resolve_init(struct btf_verifier_env *env)
@ -2006,10 +2052,15 @@ const struct file_operations btf_fops = {
.release = btf_release,
};
static int __btf_new_fd(struct btf *btf)
{
return anon_inode_getfd("btf", &btf_fops, btf, O_RDONLY | O_CLOEXEC);
}
int btf_new_fd(const union bpf_attr *attr)
{
struct btf *btf;
int fd;
int ret;
btf = btf_parse(u64_to_user_ptr(attr->btf),
attr->btf_size, attr->btf_log_level,
@ -2018,12 +2069,23 @@ int btf_new_fd(const union bpf_attr *attr)
if (IS_ERR(btf))
return PTR_ERR(btf);
fd = anon_inode_getfd("btf", &btf_fops, btf,
O_RDONLY | O_CLOEXEC);
if (fd < 0)
ret = btf_alloc_id(btf);
if (ret) {
btf_free(btf);
return ret;
}
/*
* The BTF ID is published to the userspace.
* All BTF free must go through call_rcu() from
* now on (i.e. free by calling btf_put()).
*/
ret = __btf_new_fd(btf);
if (ret < 0)
btf_put(btf);
return fd;
return ret;
}
struct btf *btf_get_by_fd(int fd)
@ -2042,7 +2104,7 @@ struct btf *btf_get_by_fd(int fd)
}
btf = f.file->private_data;
btf_get(btf);
refcount_inc(&btf->refcnt);
fdput(f);
return btf;
@ -2062,3 +2124,29 @@ int btf_get_info_by_fd(const struct btf *btf,
return 0;
}
int btf_get_fd_by_id(u32 id)
{
struct btf *btf;
int fd;
rcu_read_lock();
btf = idr_find(&btf_idr, id);
if (!btf || !refcount_inc_not_zero(&btf->refcnt))
btf = ERR_PTR(-ENOENT);
rcu_read_unlock();
if (IS_ERR(btf))
return PTR_ERR(btf);
fd = __btf_new_fd(btf);
if (fd < 0)
btf_put(btf);
return fd;
}
u32 btf_id(const struct btf *btf)
{
return btf->id;
}

View File

@ -252,7 +252,6 @@ static void bpf_map_free_deferred(struct work_struct *work)
bpf_map_uncharge_memlock(map);
security_bpf_map_free(map);
btf_put(map->btf);
/* implementation dependent freeing */
map->ops->map_free(map);
}
@ -273,6 +272,7 @@ static void __bpf_map_put(struct bpf_map *map, bool do_idr_lock)
if (atomic_dec_and_test(&map->refcnt)) {
/* bpf_map_free_id() must be called first */
bpf_map_free_id(map, do_idr_lock);
btf_put(map->btf);
INIT_WORK(&map->work, bpf_map_free_deferred);
schedule_work(&map->work);
}
@ -2002,6 +2002,12 @@ static int bpf_map_get_info_by_fd(struct bpf_map *map,
info.map_flags = map->map_flags;
memcpy(info.name, map->name, sizeof(map->name));
if (map->btf) {
info.btf_id = btf_id(map->btf);
info.btf_key_id = map->btf_key_id;
info.btf_value_id = map->btf_value_id;
}
if (bpf_map_is_dev_bound(map)) {
err = bpf_map_offload_info_fill(&info, map);
if (err)
@ -2059,6 +2065,19 @@ static int bpf_btf_load(const union bpf_attr *attr)
return btf_new_fd(attr);
}
#define BPF_BTF_GET_FD_BY_ID_LAST_FIELD btf_id
static int bpf_btf_get_fd_by_id(const union bpf_attr *attr)
{
if (CHECK_ATTR(BPF_BTF_GET_FD_BY_ID))
return -EINVAL;
if (!capable(CAP_SYS_ADMIN))
return -EPERM;
return btf_get_fd_by_id(attr->btf_id);
}
SYSCALL_DEFINE3(bpf, int, cmd, union bpf_attr __user *, uattr, unsigned int, size)
{
union bpf_attr attr = {};
@ -2142,6 +2161,9 @@ SYSCALL_DEFINE3(bpf, int, cmd, union bpf_attr __user *, uattr, unsigned int, siz
case BPF_BTF_LOAD:
err = bpf_btf_load(&attr);
break;
case BPF_BTF_GET_FD_BY_ID:
err = bpf_btf_get_fd_by_id(&attr);
break;
default:
err = -EINVAL;
break;