Merge branch 'bpf_iter'

Yonghong Song says:

====================
Motivation:
  The current way to dump kernel data structures mostly:
    1. /proc system
    2. various specific tools like "ss" which requires kernel support.
    3. drgn
  The dropback for the first two is that whenever you want to dump more, you
  need change the kernel. For example, Martin wants to dump socket local
  storage with "ss". Kernel change is needed for it to work ([1]).
  This is also the direct motivation for this work.

  drgn ([2]) solves this proble nicely and no kernel change is not needed.
  But since drgn is not able to verify the validity of a particular pointer value,
  it might present the wrong results in rare cases.

  In this patch set, we introduce bpf iterator. Initial kernel changes are
  still needed for interested kernel data, but a later data structure change
  will not require kernel changes any more. bpf program itself can adapt
  to new data structure changes. This will give certain flexibility with
  guaranteed correctness.

  In this patch set, kernel seq_ops is used to facilitate iterating through
  kernel data, similar to current /proc and many other lossless kernel
  dumping facilities. In the future, different iterators can be
  implemented to trade off losslessness for other criteria e.g. no
  repeated object visits, etc.

User Interface:
  1. Similar to prog/map/link, the iterator can be pinned into a
     path within a bpffs mount point.
  2. The bpftool command can pin an iterator to a file
         bpftool iter pin <bpf_prog.o> <path>
  3. Use `cat <path>` to dump the contents.
     Use `rm -f <path>` to remove the pinned iterator.
  4. The anonymous iterator can be created as well.

  Please see patch #19 andd #20 for bpf programs and bpf iterator
  output examples.

  Note that certain iterators are namespace aware. For example,
  task and task_file targets only iterate through current pid namespace.
  ipv6_route and netlink will iterate through current net namespace.

  Please see individual patches for implementation details.

Performance:
  The bpf iterator provides in-kernel aggregation abilities
  for kernel data. This can greatly improve performance
  compared to e.g., iterating all process directories under /proc.
  For example, I did an experiment on my VM with an application forking
  different number of tasks and each forked process opening various number
  of files. The following is the result with the latency with unit of microseconds:

    # of forked tasks   # of open files    # of bpf_prog calls  # latency (us)
    100                 100                11503                7586
    1000                1000               1013203              709513
    10000               100                1130203              764519

  The number of bpf_prog calls may be more than forked tasks multipled by
  open files since there are other tasks running on the system.
  The bpf program is a do-nothing program. One millions of bpf calls takes
  less than one second.

  Although the initial motivation is from Martin's sk_local_storage,
  this patch didn't implement tcp6 sockets and sk_local_storage.
  The /proc/net/tcp6 involves three types of sockets, timewait,
  request and tcp6 sockets. Some kind of type casting or other
  mechanism is needed to handle all these socket types in one
  bpf program. This will be addressed in future work.

  Currently, we do not support kernel data generated under module.
  This requires some BTF work.

  More work for more iterators, e.g., tcp, udp, bpf_map elements, etc.

Changelog:
  v3 -> v4:
    - in bpf_seq_read(), if start() failed with an error, return that
      error to user space (Andrii)
    - in bpf_seq_printf(), if reading kernel memory failed for
      %s and %p{i,I}{4,6}, set buffer to empty string or address 0.
      Documented this behavior in uapi header (Andrii)
    - fix a few error handling issues for bpftool (Andrii)
    - A few other minor fixes and cosmetic changes.
  v2 -> v3:
    - add bpf_iter_unreg_target() to unregister a target, used in the
      error path of the __init functions.
    - handle err != 0 before handling overflow (Andrii)
    - reference count "task" for task_file target (Andrii)
    - remove some redundancy for bpf_map/task/task_file targets
    - add bpf_iter_unreg_target() in ip6_route_cleanup()
    - Handling "%%" format in bpf_seq_printf() (Andrii)
    - implement auto-attach for bpf_iter in libbpf (Andrii)
    - add macros offsetof and container_of in bpf_helpers.h (Andrii)
    - add tests for auto-attach and program-return-1 cases
    - some other minor fixes
  v1 -> v2:
    - removed target_feature, using callback functions instead
    - checking target to ensure program specified btf_id supported (Martin)
    - link_create change with new changes from Andrii
    - better handling of btf_iter vs. seq_file private data (Martin, Andrii)
    - implemented bpf_seq_read() (Andrii, Alexei)
    - percpu buffer for bpf_seq_printf() (Andrii)
    - better syntax for BPF_SEQ_PRINTF macro (Andrii)
    - bpftool fixes (Quentin)
    - a lot of other fixes
  RFC v2 -> v1:
    - rename bpfdump to bpf_iter
    - use bpffs instead of a new file system
    - use bpf_link to streamline and simplify iterator creation.

References:
  [1]: https://lore.kernel.org/bpf/20200225230427.1976129-1-kafai@fb.com
  [2]: https://github.com/osandov/drgn
====================

Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 36 insertions, 0 deletions

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 1262ec460ab3..cf4b6e44f2bc 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -31,6 +31,7 @@ struct seq_file;
 struct btf;
 struct btf_type;
 struct exception_table_entry;
+struct seq_operations;
 
 extern struct idr btf_idr;
 extern spinlock_t btf_idr_lock;
@@ -319,6 +320,7 @@ enum bpf_reg_type {
 	PTR_TO_TP_BUFFER,	 /* reg points to a writable raw tp's buffer */
 	PTR_TO_XDP_SOCK,	 /* reg points to struct xdp_sock */
 	PTR_TO_BTF_ID,		 /* reg points to kernel struct */
+	PTR_TO_BTF_ID_OR_NULL,	 /* reg points to kernel struct or NULL */
 };
 
 /* The information passed from prog-specific *_is_valid_access
@@ -657,6 +659,7 @@ struct bpf_prog_aux {
 	bool offload_requested;
 	bool attach_btf_trace; /* true if attaching to BTF-enabled raw tp */
 	bool func_proto_unreliable;
+	bool btf_id_or_null_non0_off;
 	enum bpf_tramp_prog_type trampoline_prog_type;
 	struct bpf_trampoline *trampoline;
 	struct hlist_node tramp_hlist;
@@ -1021,6 +1024,7 @@ static inline void bpf_enable_instrumentation(void)
 
 extern const struct file_operations bpf_map_fops;
 extern const struct file_operations bpf_prog_fops;
+extern const struct file_operations bpf_iter_fops;
 
 #define BPF_PROG_TYPE(_id, _name, prog_ctx_type, kern_ctx_type) \
 	extern const struct bpf_prog_ops _name ## _prog_ops; \
@@ -1080,6 +1084,7 @@ int  generic_map_update_batch(struct bpf_map *map,
 int  generic_map_delete_batch(struct bpf_map *map,
 			      const union bpf_attr *attr,
 			      union bpf_attr __user *uattr);
+struct bpf_map *bpf_map_get_curr_or_next(u32 *id);
 
 extern int sysctl_unprivileged_bpf_disabled;
 
@@ -1126,6 +1131,37 @@ struct bpf_link *bpf_link_get_from_fd(u32 ufd);
 int bpf_obj_pin_user(u32 ufd, const char __user *pathname);
 int bpf_obj_get_user(const char __user *pathname, int flags);
 
+#define BPF_ITER_FUNC_PREFIX "__bpf_iter__"
+#define DEFINE_BPF_ITER_FUNC(target, args...)			\
+	extern int __bpf_iter__ ## target(args);		\
+	int __init __bpf_iter__ ## target(args) { return 0; }
+
+typedef int (*bpf_iter_init_seq_priv_t)(void *private_data);
+typedef void (*bpf_iter_fini_seq_priv_t)(void *private_data);
+
+struct bpf_iter_reg {
+	const char *target;
+	const struct seq_operations *seq_ops;
+	bpf_iter_init_seq_priv_t init_seq_private;
+	bpf_iter_fini_seq_priv_t fini_seq_private;
+	u32 seq_priv_size;
+};
+
+struct bpf_iter_meta {
+	__bpf_md_ptr(struct seq_file *, seq);
+	u64 session_id;
+	u64 seq_num;
+};
+
+int bpf_iter_reg_target(struct bpf_iter_reg *reg_info);
+void bpf_iter_unreg_target(const char *target);
+bool bpf_iter_prog_supported(struct bpf_prog *prog);
+int bpf_iter_link_attach(const union bpf_attr *attr, struct bpf_prog *prog);
+int bpf_iter_new_fd(struct bpf_link *link);
+bool bpf_link_is_iter(struct bpf_link *link);
+struct bpf_prog *bpf_iter_get_info(struct bpf_iter_meta *meta, bool in_stop);
+int bpf_iter_run_prog(struct bpf_prog *prog, void *ctx);
+
 int bpf_percpu_hash_copy(struct bpf_map *map, void *key, void *value);
 int bpf_percpu_array_copy(struct bpf_map *map, void *key, void *value);
 int bpf_percpu_hash_update(struct bpf_map *map, void *key, void *value,