bpf: Enable task local storage for tracing programs

To access per-task data, BPF programs usually creates a hash table with
pid as the key. This is not ideal because:
 1. The user need to estimate the proper size of the hash table, which may
    be inaccurate;
 2. Big hash tables are slow;
 3. To clean up the data properly during task terminations, the user need
    to write extra logic.

Task local storage overcomes these issues and offers a better option for
these per-task data. Task local storage is only available to BPF_LSM. Now
enable it for tracing programs.

Unlike LSM programs, tracing programs can be called in IRQ contexts.
Helpers that access task local storage are updated to use
raw_spin_lock_irqsave() instead of raw_spin_lock_bh().

Tracing programs can attach to functions on the task free path, e.g.
exit_creds(). To avoid allocating task local storage after
bpf_task_storage_free(). bpf_task_storage_get() is updated to not allocate
new storage when the task is not refcounted (task->usage == 0).

Signed-off-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: KP Singh <kpsingh@kernel.org>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Link: https://lore.kernel.org/bpf/20210225234319.336131-2-songliubraving@fb.com

4 files changed, 13 insertions, 23 deletions

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index cccaef1088ea..e2cfc4809219 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -1499,6 +1499,7 @@ struct bpf_prog *bpf_prog_by_id(u32 id);
 struct bpf_link *bpf_link_by_id(u32 id);
 
 const struct bpf_func_proto *bpf_base_func_proto(enum bpf_func_id func_id);
+void bpf_task_storage_free(struct task_struct *task);
 #else /* !CONFIG_BPF_SYSCALL */
 static inline struct bpf_prog *bpf_prog_get(u32 ufd)
 {
@@ -1684,6 +1685,10 @@ bpf_base_func_proto(enum bpf_func_id func_id)
 {
 	return NULL;
 }
+
+static inline void bpf_task_storage_free(struct task_struct *task)
+{
+}
 #endif /* CONFIG_BPF_SYSCALL */
 
 void __bpf_free_used_btfs(struct bpf_prog_aux *aux,
@@ -1886,6 +1891,8 @@ extern const struct bpf_func_proto bpf_this_cpu_ptr_proto;
 extern const struct bpf_func_proto bpf_ktime_get_coarse_ns_proto;
 extern const struct bpf_func_proto bpf_sock_from_file_proto;
 extern const struct bpf_func_proto bpf_get_socket_ptr_cookie_proto;
+extern const struct bpf_func_proto bpf_task_storage_get_proto;
+extern const struct bpf_func_proto bpf_task_storage_delete_proto;
 
 const struct bpf_func_proto *bpf_tracing_func_proto(
 	enum bpf_func_id func_id, const struct bpf_prog *prog);
diff --git a/include/linux/bpf_lsm.h b/include/linux/bpf_lsm.h
index 0d1c33ace398..479c101546ad 100644
--- a/include/linux/bpf_lsm.h
+++ b/include/linux/bpf_lsm.h
@@ -38,21 +38,9 @@ static inline struct bpf_storage_blob *bpf_inode(
 	return inode->i_security + bpf_lsm_blob_sizes.lbs_inode;
 }
 
-static inline struct bpf_storage_blob *bpf_task(
-	const struct task_struct *task)
-{
-	if (unlikely(!task->security))
-		return NULL;
-
-	return task->security + bpf_lsm_blob_sizes.lbs_task;
-}
-
 extern const struct bpf_func_proto bpf_inode_storage_get_proto;
 extern const struct bpf_func_proto bpf_inode_storage_delete_proto;
-extern const struct bpf_func_proto bpf_task_storage_get_proto;
-extern const struct bpf_func_proto bpf_task_storage_delete_proto;
 void bpf_inode_storage_free(struct inode *inode);
-void bpf_task_storage_free(struct task_struct *task);
 
 #else /* !CONFIG_BPF_LSM */
 
@@ -73,20 +61,10 @@ static inline struct bpf_storage_blob *bpf_inode(
 	return NULL;
 }
 
-static inline struct bpf_storage_blob *bpf_task(
-	const struct task_struct *task)
-{
-	return NULL;
-}
-
 static inline void bpf_inode_storage_free(struct inode *inode)
 {
 }
 
-static inline void bpf_task_storage_free(struct task_struct *task)
-{
-}
-
 #endif /* CONFIG_BPF_LSM */
 
 #endif /* _LINUX_BPF_LSM_H */
diff --git a/include/linux/bpf_types.h b/include/linux/bpf_types.h
index 99f7fd657d87..b9edee336d80 100644
--- a/include/linux/bpf_types.h
+++ b/include/linux/bpf_types.h
@@ -109,8 +109,8 @@ BPF_MAP_TYPE(BPF_MAP_TYPE_SOCKHASH, sock_hash_ops)
 #endif
 #ifdef CONFIG_BPF_LSM
 BPF_MAP_TYPE(BPF_MAP_TYPE_INODE_STORAGE, inode_storage_map_ops)
-BPF_MAP_TYPE(BPF_MAP_TYPE_TASK_STORAGE, task_storage_map_ops)
 #endif
+BPF_MAP_TYPE(BPF_MAP_TYPE_TASK_STORAGE, task_storage_map_ops)
 BPF_MAP_TYPE(BPF_MAP_TYPE_CPUMAP, cpu_map_ops)
 #if defined(CONFIG_XDP_SOCKETS)
 BPF_MAP_TYPE(BPF_MAP_TYPE_XSKMAP, xsk_map_ops)
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 4d568288abf9..e5fbf8e6952a 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -42,6 +42,7 @@ struct audit_context;
 struct backing_dev_info;
 struct bio_list;
 struct blk_plug;
+struct bpf_local_storage;
 struct capture_control;
 struct cfs_rq;
 struct fs_struct;
@@ -1348,6 +1349,10 @@ struct task_struct {
 	/* Used by LSM modules for access restriction: */
 	void				*security;
 #endif
+#ifdef CONFIG_BPF_SYSCALL
+	/* Used by BPF task local storage */
+	struct bpf_local_storage __rcu	*bpf_storage;
+#endif
 
 #ifdef CONFIG_GCC_PLUGIN_STACKLEAK
 	unsigned long			lowest_stack;