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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
arch Power management updates for 5.17-rc1 2022-01-10 20:34:00 -08:00
block block-5.16-2021-12-19 2021-12-19 12:38:53 -08:00
certs certs: Add support for using elliptic curve keys for signing modules 2021-08-23 19:55:42 +03:00
crypto lib/crypto: blake2s: include as built-in 2022-01-07 00:25:25 +01:00
Documentation Device properties framework updates for 5.17-rc1 2022-01-10 20:48:19 -08:00
drivers Device properties framework updates for 5.17-rc1 2022-01-10 20:48:19 -08:00
fs Networking changes for 5.17. 2022-01-10 19:06:09 -08:00
include bpf: Add reference tracking support to kfunc 2022-01-18 14:26:42 -08:00
init Power management updates for 5.17-rc1 2022-01-10 20:34:00 -08:00
ipc shm: extend forced shm destroy to support objects from several IPC nses 2021-11-20 10:35:54 -08:00
kernel bpf: Add reference tracking support to kfunc 2022-01-18 14:26:42 -08:00
lib Networking changes for 5.17. 2022-01-10 19:06:09 -08:00
LICENSES LICENSES/dual/CC-BY-4.0: Git rid of "smart quotes" 2021-07-15 06:31:24 -06:00
mm slab changes for 5.17 2022-01-10 11:58:12 -08:00
net bpf: Remove check_kfunc_call callback and old kfunc BTF ID API 2022-01-18 14:26:41 -08:00
samples samples/bpf: Stop using bpf_map__def() API 2022-01-12 17:01:38 -08:00
scripts bpf/scripts: Raise an exception if the correct number of helpers are not generated 2022-01-14 16:47:34 -08:00
security Merge git://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next 2021-12-31 14:35:40 +00:00
sound sound fixes for 5.16-rc7 2021-12-23 09:55:58 -08:00
tools bpf: Remove check_kfunc_call callback and old kfunc BTF ID API 2022-01-18 14:26:41 -08:00
usr initramfs: Check timestamp to prevent broken cpio archive 2021-10-24 13:48:40 +09:00
virt KVM: downgrade two BUG_ONs to WARN_ON_ONCE 2021-11-26 06:43:28 -05:00
.clang-format clang-format: Update with the latest for_each macro list 2021-05-12 23:32:39 +02:00
.cocciconfig
.get_maintainer.ignore Opt out of scripts/get_maintainer.pl 2019-05-16 10:53:40 -07:00
.gitattributes .gitattributes: use 'dts' diff driver for dts files 2019-12-04 19:44:11 -08:00
.gitignore .gitignore: ignore only top-level modules.builtin 2021-05-02 00:43:35 +09:00
.mailmap media updates for v5.17-rc1 2022-01-10 18:55:43 -08:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: Move Daniel Drake to credits 2021-09-21 08:34:58 +03:00
Kbuild kbuild: rename hostprogs-y/always to hostprogs/always-y 2020-02-04 01:53:07 +09:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS Device properties framework updates for 5.17-rc1 2022-01-10 20:48:19 -08:00
Makefile Linux 5.16 2022-01-09 14:55:34 -08:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -06:00

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.