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linux/kernel/bpf
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Kumar Kartikeya Dwivedi 5c073f26f9 bpf: Add reference tracking support to kfunc 
This patch adds verifier support for PTR_TO_BTF_ID return type of kfunc
to be a reference, by reusing acquire_reference_state/release_reference
support for existing in-kernel bpf helpers.

We make use of the three kfunc types:

- BTF_KFUNC_TYPE_ACQUIRE
  Return true if kfunc_btf_id is an acquire kfunc.  This will
  acquire_reference_state for the returned PTR_TO_BTF_ID (this is the
  only allow return value). Note that acquire kfunc must always return a
  PTR_TO_BTF_ID{_OR_NULL}, otherwise the program is rejected.

- BTF_KFUNC_TYPE_RELEASE
  Return true if kfunc_btf_id is a release kfunc.  This will release the
  reference to the passed in PTR_TO_BTF_ID which has a reference state
  (from earlier acquire kfunc).
  The btf_check_func_arg_match returns the regno (of argument register,
  hence > 0) if the kfunc is a release kfunc, and a proper referenced
  PTR_TO_BTF_ID is being passed to it.
  This is similar to how helper call check uses bpf_call_arg_meta to
  store the ref_obj_id that is later used to release the reference.
  Similar to in-kernel helper, we only allow passing one referenced
  PTR_TO_BTF_ID as an argument. It can also be passed in to normal
  kfunc, but in case of release kfunc there must always be one
  PTR_TO_BTF_ID argument that is referenced.

- BTF_KFUNC_TYPE_RET_NULL
  For kfunc returning PTR_TO_BTF_ID, tells if it can be NULL, hence
  force caller to mark the pointer not null (using check) before
  accessing it. Note that taking into account the case fixed by commit
  93c230e3f5 ("bpf: Enforce id generation for all may-be-null register type")
  we assign a non-zero id for mark_ptr_or_null_reg logic. Later, if more
  return types are supported by kfunc, which have a _OR_NULL variant, it
  might be better to move this id generation under a common
  reg_type_may_be_null check, similar to the case in the commit.

Referenced PTR_TO_BTF_ID is currently only limited to kfunc, but can be
extended in the future to other BPF helpers as well.  For now, we can
rely on the btf_struct_ids_match check to ensure we get the pointer to
the expected struct type. In the future, care needs to be taken to avoid
ambiguity for reference PTR_TO_BTF_ID passed to release function, in
case multiple candidates can release same BTF ID.

e.g. there might be two release kfuncs (or kfunc and helper):

foo(struct abc *p);
bar(struct abc *p);

... such that both release a PTR_TO_BTF_ID with btf_id of struct abc. In
this case we would need to track the acquire function corresponding to
the release function to avoid type confusion, and store this information
in the register state so that an incorrect program can be rejected. This
is not a problem right now, hence it is left as an exercise for the
future patch introducing such a case in the kernel.

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Link: https://lore.kernel.org/r/20220114163953.1455836-6-memxor@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
2022-01-18 14:26:42 -08:00
..
preload bpf/preload: Clean up .gitignore and "clean-files" target 2021-10-20 10:39:04 -07:00
arraymap.c Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net 2021-10-28 10:43:58 -07:00
bloom_filter.c bpf: Add missing map_get_next_key method to bloom filter map. 2021-12-29 09:38:31 -08:00
bpf_inode_storage.c bpf: Allow bpf_local_storage to be used by sleepable programs 2021-12-29 17:54:40 -08:00
bpf_iter.c bpf: Add bpf_loop helper 2021-11-30 10:56:28 -08:00
bpf_local_storage.c bpf: Allow bpf_local_storage to be used by sleepable programs 2021-12-29 17:54:40 -08:00
bpf_lru_list.c bpf_lru_list: Read double-checked variable once without lock 2021-02-10 15:54:26 -08:00
bpf_lru_list.h
bpf_lsm.c Merge git://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next 2021-06-17 11:54:56 -07:00
bpf_struct_ops.c bpf: Rename btf_member accessors. 2021-12-02 11:18:34 -08:00
bpf_struct_ops_types.h bpf: Add dummy BPF STRUCT_OPS for test purpose 2021-11-01 14:10:00 -07:00
bpf_task_storage.c bpf: Allow bpf_local_storage to be used by sleepable programs 2021-12-29 17:54:40 -08:00
btf.c bpf: Add reference tracking support to kfunc 2022-01-18 14:26:42 -08:00
cgroup.c bpf: Add MEM_RDONLY for helper args that are pointers to rdonly mem. 2021-12-18 13:27:41 -08:00
core.c bpf, docs: Prune all references to "internal BPF" 2021-11-30 10:52:11 -08:00
cpumap.c xdp: Move conversion to xdp_frame out of map functions 2022-01-05 19:46:32 -08:00
devmap.c xdp: Move conversion to xdp_frame out of map functions 2022-01-05 19:46:32 -08:00
disasm.c bpf: Relicense disassembler as GPL-2.0-only OR BSD-2-Clause 2021-09-02 14:49:23 +02:00
disasm.h bpf: Relicense disassembler as GPL-2.0-only OR BSD-2-Clause 2021-09-02 14:49:23 +02:00
dispatcher.c
hashtab.c bpf: Replace callers of BPF_CAST_CALL with proper function typedef 2021-09-28 16:27:18 -07:00
helpers.c bpf: Add MEM_RDONLY for helper args that are pointers to rdonly mem. 2021-12-18 13:27:41 -08:00
inode.c bpf: Fix regression on BPF_OBJ_GET with non-O_RDWR flags 2021-06-22 14:57:43 +02:00
Kconfig bpf: Disallow unprivileged bpf by default 2021-11-01 17:06:47 +01:00
local_storage.c bpf: Use struct_size() helper 2021-12-21 15:35:48 -08:00
lpm_trie.c bpf: Fix typo in a comment in bpf lpm_trie. 2021-12-30 18:42:34 -08:00
Makefile bpf: Prepare relo_core.c for kernel duty. 2021-12-02 11:18:34 -08:00
map_in_map.c bpf: Remember BTF of inner maps. 2021-07-15 22:31:10 +02:00
map_in_map.h
map_iter.c bpf: Introduce MEM_RDONLY flag 2021-12-18 13:27:41 -08:00
mmap_unlock_work.h bpf: Introduce helper bpf_find_vma 2021-11-07 11:54:51 -08:00
net_namespace.c net: Add includes masked by netdevice.h including uapi/bpf.h 2021-12-29 20:03:05 -08:00
offload.c
percpu_freelist.c
percpu_freelist.h
prog_iter.c
queue_stack_maps.c bpf: Eliminate rlimit-based memory accounting for queue_stack_maps maps 2020-12-02 18:32:46 -08:00
reuseport_array.c bpf: Use struct_size() helper 2021-12-21 15:35:48 -08:00
ringbuf.c bpf: Add MEM_RDONLY for helper args that are pointers to rdonly mem. 2021-12-18 13:27:41 -08:00
stackmap.c bpf: Introduce btf_tracing_ids 2021-11-12 10:19:09 -08:00
syscall.c bpf: Add MEM_RDONLY for helper args that are pointers to rdonly mem. 2021-12-18 13:27:41 -08:00
sysfs_btf.c bpf: Load and verify kernel module BTFs 2020-11-10 15:25:53 -08:00
task_iter.c bpf: Introduce btf_tracing_ids 2021-11-12 10:19:09 -08:00
tnum.c bpf, tnums: Provably sound, faster, and more precise algorithm for tnum_mul 2021-06-01 13:34:15 +02:00
trampoline.c bpf: Add get_func_[arg|ret|arg_cnt] helpers 2021-12-13 09:25:59 -08:00
verifier.c bpf: Add reference tracking support to kfunc 2022-01-18 14:26:42 -08:00