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Commit 78958fca authored by Martin KaFai Lau's avatar Martin KaFai Lau Committed by Daniel Borkmann
Browse files

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: default avatarMartin KaFai Lau <kafai@fb.com>
Acked-by: default avatarAlexei Starovoitov <ast@fb.com>
Acked-by: default avatarSong Liu <songliubraving@fb.com>
Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
parent 82e96972

include/linux/btf.h

+2 −0
Original line number Diff line number Diff line
@@ -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

include/uapi/linux/bpf.h

+5 −0
Original line number Diff line number Diff line
@@ -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

kernel/bpf/btf.c

+98 −10
Original line number Diff line number Diff line
@@ -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;

}

kernel/bpf/syscall.c

+23 −1
Original line number Diff line number Diff line
@@ -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;