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Introduce unstable CT lookup helpers #2347

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Introduce unstable CT lookup helpers #2347

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Pull request for series with
subject: Introduce unstable CT lookup helpers
version: 5
url: https://patchwork.kernel.org/project/netdevbpf/list/?series=601958

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Master branch: 1705c62
series: https://patchwork.kernel.org/project/netdevbpf/list/?series=601958
version: 5

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Master branch: 35580f9
series: https://patchwork.kernel.org/project/netdevbpf/list/?series=601958
version: 5

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Master branch: 35580f9
series: https://patchwork.kernel.org/project/netdevbpf/list/?series=601958
version: 5

Nobody and others added 9 commits December 30, 2021 16:49
adding ci files
a504cac
@kkdwivedi
kernel: Add kallsyms_on_each_symbol variant for single module
631cff3 
The module_kallsyms_on_each_symbol function iterates over symbols of all
modules. To implement BTF ID set processing in each module's BTF parsing
routine, we need a variant that can iterate over a single module's
symbols. To implement this, extract the single module functionality out
of module_kallsyms_on_each_symbol, and rename the old function to
module_kallsyms_on_each_symbol_all.

Then, the new module_kallsyms_on_each_symbol which iterates over a
single module's symbols uses this extracted helper with appropriate
locking.

Next commit will make use of it to implement BTF ID set concatentation
per hook and type.

Also, since we'll be using kallsyms_on_each_symbol for vmlinux BTF
parsing, remove its dependency on CONFIG_LIVEPATCH.

Cc: Luis Chamberlain <mcgrof@kernel.org>
Cc: Jessica Yu <jeyu@kernel.org>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Jiri Kosina <jikos@kernel.org>
Cc: Miroslav Benes <mbenes@suse.cz>
Cc: Petr Mladek <pmladek@suse.com>
Cc: Joe Lawrence <joe.lawrence@redhat.com>
Cc: live-patching@vger.kernel.org
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
@kkdwivedi
bpf: Prepare kfunc BTF ID sets when parsing kernel BTF
37e1edd 
This commit prepares the BTF parsing functions for vmlinux and module
BTFs to find all kfunc BTF ID sets from the vmlinux and module symbols
and concatentate all sets into single unified set which is sorted and
keyed by the 'hook' it is meant for, and 'type' of set.

The 'hook' is one of the many program types, e.g. XDP and TC/SCHED_CLS,
STRUCT_OPS, and 'types' are check (allowed or not), acquire, release,
and ret_null (with PTR_TO_BTF_ID_OR_NULL return type).

A maximum of BTF_KFUNC_SET_MAX_CNT (32) kfunc BTF IDs are permitted in a
set of certain hook and type. They are also allocated on demand, and
otherwise set as NULL.

A new btf_kfunc_id_set_contains function is exposed for use in verifier,
this new method is faster than the existing list searching method, and
is also automatic. It also lets other code not care whether the set is
unallocated or not.

Next commit will update the kernel users to make use of this
infrastructure.

Finally, add __maybe_unused annotation for BTF ID macros for the
!CONFIG_DEBUG_INFO_BTF case , so that they don't produce warnings during
build time.

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>

fixup maybe_unused
@kkdwivedi
bpf: Remove check_kfunc_call callback and old kfunc BTF ID API
6356f68 
Completely remove the old code for check_kfunc_call to help it work
with modules.

The previous commit finds all symbols in vmlinux or modules while
parsing and preparing their BTF, and concatenates all related sets
organized by the hook and the type. Then, they are sorted to enable
bsearch using btf_id_set_contains.

Also, since we don't need the 'owner' module anywhere when doing
check_kfunc_call, drop the 'btf_modp' module parameter from
find_kfunc_desc_btf.

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
@kkdwivedi
bpf: Introduce mem, size argument pair support for kfunc
32ded3b 
BPF helpers can associate two adjacent arguments together to pass memory
of certain size, using ARG_PTR_TO_MEM and ARG_CONST_SIZE arguments.
Since we don't use bpf_func_proto for kfunc, we need to leverage BTF to
implement similar support.

The ARG_CONST_SIZE processing for helpers is refactored into a common
check_mem_size_reg helper that is shared with kfunc as well. kfunc
ptr_to_mem support follows logic similar to global functions, where
verification is done as if pointer is not null, even when it may be
null.

This leads to a simple to follow rule for writing kfunc: always check
the argument pointer for NULL, except when it is PTR_TO_CTX. Also, the
PTR_TO_CTX case is also only safe when the helper expecting pointer to
program ctx is not exposed to other programs where same struct is not
ctx type. In that case, the type check will fall through to other cases
and would permit passing other types of pointers, possibly NULL at
runtime.

Currently, we require the size argument to be suffixed with "__sz" in
the parameter name. This information is then recorded in kernel BTF and
verified during function argument checking. In the future we can use BTF
tagging instead, and modify the kernel function definitions. This will
be a purely kernel-side change.

This allows us to have some form of backwards compatibility for
structures that are passed in to the kernel function with their size,
and allow variable length structures to be passed in if they are
accompanied by a size parameter.

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
@kkdwivedi
bpf: Add reference tracking support to kfunc
c5ce7cf 
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
  93c230e ("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>
@kkdwivedi
net/netfilter: Add unstable CT lookup helpers for XDP and TC-BPF
e20eb2c 
This change adds conntrack lookup helpers using the unstable kfunc call
interface for the XDP and TC-BPF hooks. The primary usecase is
implementing a synproxy in XDP, see Maxim's patchset [0].

Export get_net_ns_by_id as nf_conntrack_bpf.c needs to call it.

This object is only built when CONFIG_DEBUG_INFO_BTF_MODULES is enabled.

  [0]: https://lore.kernel.org/bpf/20211019144655.3483197-1-maximmi@nvidia.com

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
@kkdwivedi
selftests/bpf: Add test for unstable CT lookup API
20c8e28 
This tests that we return errors as documented, and also that the kfunc
calls work from both XDP and TC hooks.

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
@kkdwivedi
selftests/bpf: Add test_verifier support to fixup kfunc call insns
208962e 
This allows us to add tests (esp. negative tests) where we only want to
ensure the program doesn't pass through the verifier, and also verify
the error. The next commit will add the tests making use of this.

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
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Master branch: 63d000c
series: https://patchwork.kernel.org/project/netdevbpf/list/?series=601958
version: 5

@kkdwivedi
selftests/bpf: Extend kfunc selftests
00d4316 
Use the prog_test kfuncs to test the referenced PTR_TO_BTF_ID kfunc
support, and PTR_TO_CTX, PTR_TO_MEM argument passing support. Also
testing the various failure cases for invalid kfunc prototypes.

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
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At least one diff in series https://patchwork.kernel.org/project/netdevbpf/list/?series=601958 expired. Closing PR.

@kernel-patches-bot kernel-patches-bot deleted the series/572999=>bpf-next branch January 2, 2022 10:33
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