According to the documentation, when building a kernel with the C=2
parameter, all source files should be checked. But this does not happen
for the kernel/bpf/ directory.

$ touch kernel/bpf/core.o
$ make C=2 CHECK=true kernel/bpf/core.o

Outputs:

  CHECK   scripts/mod/empty.c
  CALL    scripts/checksyscalls.sh
  DESCEND objtool
  INSTALL libsubcmd_headers
  CC      kernel/bpf/core.o

As can be seen the compilation is done, but CHECK is not executed. This
happens because kernel/bpf/Makefile has defined its own rule for
compilation and forgotten the macro that does the check.

There is no need to duplicate the build code, and this rule can be
removed to use generic rules.

Acked-by: Masahiro Yamada <masahiroy@kernel.org>
Tested-by: Oleg Nesterov <oleg@redhat.com>
Tested-by: Alan Maguire <alan.maguire@oracle.com>
Signed-off-by: Alexey Gladkov <legion@kernel.org>
Link: https://lore.kernel.org/r/20240830074350.211308-1-legion@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

Share relocation implementation with the kernel.  As part of this,
we also need the type/string iteration functions so also share
btf_iter.c file. Relocation code in kernel and userspace is identical
save for the impementation of the reparenting of split BTF to the
relocated base BTF and retrieval of the BTF header from "struct btf";
these small functions need separate user-space and kernel implementations
for the separate "struct btf"s they operate upon.

One other wrinkle on the kernel side is we have to map .BTF.ids in
modules as they were generated with the type ids used at BTF encoding
time. btf_relocate() optionally returns an array mapping from old BTF
ids to relocated ids, so we use that to fix up these references where
needed for kfuncs.

Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/bpf/20240620091733.1967885-5-alan.maguire@oracle.com

Crypto subsytem can be build as a module. In this case we still have to
build BPF crypto framework otherwise the build will fail.

Fixes: 3e1c6f35409f ("bpf: make common crypto API for TC/XDP programs")
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202405011634.4JK40epY-lkp@intel.com/
Signed-off-by: Vadim Fedorenko <vadfed@meta.com>
Link: https://lore.kernel.org/r/20240501170130.1682309-1-vadfed@meta.com
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>

Daniel Borkmann says:

====================
pull-request: bpf-next 2024-04-29

We've added 147 non-merge commits during the last 32 day(s) which contain
a total of 158 files changed, 9400 insertions(+), 2213 deletions(-).

The main changes are:

1) Add an internal-only BPF per-CPU instruction for resolving per-CPU
   memory addresses and implement support in x86 BPF JIT. This allows
   inlining per-CPU array and hashmap lookups
   and the bpf_get_smp_processor_id() helper, from Andrii Nakryiko.

2) Add BPF link support for sk_msg and sk_skb programs, from Yonghong Song.

3) Optimize x86 BPF JIT's emit_mov_imm64, and add support for various
   atomics in bpf_arena which can be JITed as a single x86 instruction,
   from Alexei Starovoitov.

4) Add support for passing mark with bpf_fib_lookup helper,
   from Anton Protopopov.

5) Add a new bpf_wq API for deferring events and refactor sleepable
   bpf_timer code to keep common code where possible,
   from Benjamin Tissoires.

6) Fix BPF_PROG_TEST_RUN infra with regards to bpf_dummy_struct_ops programs
   to check when NULL is passed for non-NULLable parameters,
   from Eduard Zingerman.

7) Harden the BPF verifier's and/or/xor value tracking,
   from Harishankar Vishwanathan.

8) Introduce crypto kfuncs to make BPF programs able to utilize the kernel
   crypto subsystem, from Vadim Fedorenko.

9) Various improvements to the BPF instruction set standardization doc,
   from Dave Thaler.

10) Extend libbpf APIs to partially consume items from the BPF ringbuffer,
    from Andrea Righi.

11) Bigger batch of BPF selftests refactoring to use common network helpers
    and to drop duplicate code, from Geliang Tang.

12) Support bpf_tail_call_static() helper for BPF programs with GCC 13,
    from Jose E. Marchesi.

13) Add bpf_preempt_{disable,enable}() kfuncs in order to allow a BPF
    program to have code sections where preemption is disabled,
    from Kumar Kartikeya Dwivedi.

14) Allow invoking BPF kfuncs from BPF_PROG_TYPE_SYSCALL programs,
    from David Vernet.

15) Extend the BPF verifier to allow different input maps for a given
    bpf_for_each_map_elem() helper call in a BPF program, from Philo Lu.

16) Add support for PROBE_MEM32 and bpf_addr_space_cast instructions
    for riscv64 and arm64 JITs to enable BPF Arena, from Puranjay Mohan.

17) Shut up a false-positive KMSAN splat in interpreter mode by unpoison
    the stack memory, from Martin KaFai Lau.

18) Improve xsk selftest coverage with new tests on maximum and minimum
    hardware ring size configurations, from Tushar Vyavahare.

19) Various ReST man pages fixes as well as documentation and bash completion
    improvements for bpftool, from Rameez Rehman & Quentin Monnet.

20) Fix libbpf with regards to dumping subsequent char arrays,
    from Quentin Deslandes.

* tag 'for-netdev' of https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next: (147 commits)
  bpf, docs: Clarify PC use in instruction-set.rst
  bpf_helpers.h: Define bpf_tail_call_static when building with GCC
  bpf, docs: Add introduction for use in the ISA Internet Draft
  selftests/bpf: extend BPF_SOCK_OPS_RTT_CB test for srtt and mrtt_us
  bpf: add mrtt and srtt as BPF_SOCK_OPS_RTT_CB args
  selftests/bpf: dummy_st_ops should reject 0 for non-nullable params
  bpf: check bpf_dummy_struct_ops program params for test runs
  selftests/bpf: do not pass NULL for non-nullable params in dummy_st_ops
  selftests/bpf: adjust dummy_st_ops_success to detect additional error
  bpf: mark bpf_dummy_struct_ops.test_1 parameter as nullable
  selftests/bpf: Add ring_buffer__consume_n test.
  bpf: Add bpf_guard_preempt() convenience macro
  selftests: bpf: crypto: add benchmark for crypto functions
  selftests: bpf: crypto skcipher algo selftests
  bpf: crypto: add skcipher to bpf crypto
  bpf: make common crypto API for TC/XDP programs
  bpf: update the comment for BTF_FIELDS_MAX
  selftests/bpf: Fix wq test.
  selftests/bpf: Use make_sockaddr in test_sock_addr
  selftests/bpf: Use connect_to_addr in test_sock_addr
  ...
====================

Link: https://lore.kernel.org/r/20240429131657.19423-1-daniel@iogearbox.net
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Add crypto API support to BPF to be able to decrypt or encrypt packets
in TC/XDP BPF programs. Special care should be taken for initialization
part of crypto algo because crypto alloc) doesn't work with preemtion
disabled, it can be run only in sleepable BPF program. Also async crypto
is not supported because of the very same issue - TC/XDP BPF programs
are not sleepable.

Signed-off-by: Vadim Fedorenko <vadfed@meta.com>
Link: https://lore.kernel.org/r/20240422225024.2847039-2-vadfed@meta.com
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>

The -Woverride-init warn about code that may be intentional or not,
but the inintentional ones tend to be real bugs, so there is a bit of
disagreement on whether this warning option should be enabled by default
and we have multiple settings in scripts/Makefile.extrawarn as well as
individual subsystems.

Older versions of clang only supported -Wno-initializer-overrides with
the same meaning as gcc's -Woverride-init, though all supported versions
now work with both. Because of this difference, an earlier cleanup of
mine accidentally turned the clang warning off for W=1 builds and only
left it on for W=2, while it's still enabled for gcc with W=1.

There is also one driver that only turns the warning off for newer
versions of gcc but not other compilers, and some but not all the
Makefiles still use a cc-disable-warning conditional that is no
longer needed with supported compilers here.

Address all of the above by removing the special cases for clang
and always turning the warning off unconditionally where it got
in the way, using the syntax that is supported by both compilers.

Fixes: 2cd3271b7a31 ("kbuild: avoid duplicate warning options")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Hamza Mahfooz <hamza.mahfooz@amd.com>
Acked-by: Jani Nikula <jani.nikula@intel.com>
Acked-by: Andrew Jeffery <andrew@codeconstruct.com.au>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

Introduce bpf_arena, which is a sparse shared memory region between the bpf
program and user space.

Use cases:
1. User space mmap-s bpf_arena and uses it as a traditional mmap-ed
   anonymous region, like memcached or any key/value storage. The bpf
   program implements an in-kernel accelerator. XDP prog can search for
   a key in bpf_arena and return a value without going to user space.
2. The bpf program builds arbitrary data structures in bpf_arena (hash
   tables, rb-trees, sparse arrays), while user space consumes it.
3. bpf_arena is a "heap" of memory from the bpf program's point of view.
   The user space may mmap it, but bpf program will not convert pointers
   to user base at run-time to improve bpf program speed.

Initially, the kernel vm_area and user vma are not populated. User space
can fault in pages within the range. While servicing a page fault,
bpf_arena logic will insert a new page into the kernel and user vmas. The
bpf program can allocate pages from that region via
bpf_arena_alloc_pages(). This kernel function will insert pages into the
kernel vm_area. The subsequent fault-in from user space will populate that
page into the user vma. The BPF_F_SEGV_ON_FAULT flag at arena creation time
can be used to prevent fault-in from user space. In such a case, if a page
is not allocated by the bpf program and not present in the kernel vm_area,
the user process will segfault. This is useful for use cases 2 and 3 above.

bpf_arena_alloc_pages() is similar to user space mmap(). It allocates pages
either at a specific address within the arena or allocates a range with the
maple tree. bpf_arena_free_pages() is analogous to munmap(), which frees
pages and removes the range from the kernel vm_area and from user process
vmas.

bpf_arena can be used as a bpf program "heap" of up to 4GB. The speed of
bpf program is more important than ease of sharing with user space. This is
use case 3. In such a case, the BPF_F_NO_USER_CONV flag is recommended.
It will tell the verifier to treat the rX = bpf_arena_cast_user(rY)
instruction as a 32-bit move wX = wY, which will improve bpf prog
performance. Otherwise, bpf_arena_cast_user is translated by JIT to
conditionally add the upper 32 bits of user vm_start (if the pointer is not
NULL) to arena pointers before they are stored into memory. This way, user
space sees them as valid 64-bit pointers.

Diff https://github.com/llvm/llvm-project/pull/84410 enables LLVM BPF
backend generate the bpf_addr_space_cast() instruction to cast pointers
between address_space(1) which is reserved for bpf_arena pointers and
default address space zero. All arena pointers in a bpf program written in
C language are tagged as __attribute__((address_space(1))). Hence, clang
provides helpful diagnostics when pointers cross address space. Libbpf and
the kernel support only address_space == 1. All other address space
identifiers are reserved.

rX = bpf_addr_space_cast(rY, /* dst_as */ 1, /* src_as */ 0) tells the
verifier that rX->type = PTR_TO_ARENA. Any further operations on
PTR_TO_ARENA register have to be in the 32-bit domain. The verifier will
mark load/store through PTR_TO_ARENA with PROBE_MEM32. JIT will generate
them as kern_vm_start + 32bit_addr memory accesses. The behavior is similar
to copy_from_kernel_nofault() except that no address checks are necessary.
The address is guaranteed to be in the 4GB range. If the page is not
present, the destination register is zeroed on read, and the operation is
ignored on write.

rX = bpf_addr_space_cast(rY, 0, 1) tells the verifier that rX->type =
unknown scalar. If arena->map_flags has BPF_F_NO_USER_CONV set, then the
verifier converts such cast instructions to mov32. Otherwise, JIT will emit
native code equivalent to:
rX = (u32)rY;
if (rY)
  rX |= clear_lo32_bits(arena->user_vm_start); /* replace hi32 bits in rX */

After such conversion, the pointer becomes a valid user pointer within
bpf_arena range. The user process can access data structures created in
bpf_arena without any additional computations. For example, a linked list
built by a bpf program can be walked natively by user space.

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Reviewed-by: Barret Rhoden <brho@google.com>
Link: https://lore.kernel.org/bpf/20240308010812.89848-2-alexei.starovoitov@gmail.com

Add new kind of BPF kernel object, BPF token. BPF token is meant to
allow delegating privileged BPF functionality, like loading a BPF
program or creating a BPF map, from privileged process to a *trusted*
unprivileged process, all while having a good amount of control over which
privileged operations could be performed using provided BPF token.

This is achieved through mounting BPF FS instance with extra delegation
mount options, which determine what operations are delegatable, and also
constraining it to the owning user namespace (as mentioned in the
previous patch).

BPF token itself is just a derivative from BPF FS and can be created
through a new bpf() syscall command, BPF_TOKEN_CREATE, which accepts BPF
FS FD, which can be attained through open() API by opening BPF FS mount
point. Currently, BPF token "inherits" delegated command, map types,
prog type, and attach type bit sets from BPF FS as is. In the future,
having an BPF token as a separate object with its own FD, we can allow
to further restrict BPF token's allowable set of things either at the
creation time or after the fact, allowing the process to guard itself
further from unintentionally trying to load undesired kind of BPF
programs. But for now we keep things simple and just copy bit sets as is.

When BPF token is created from BPF FS mount, we take reference to the
BPF super block's owning user namespace, and then use that namespace for
checking all the {CAP_BPF, CAP_PERFMON, CAP_NET_ADMIN, CAP_SYS_ADMIN}
capabilities that are normally only checked against init userns (using
capable()), but now we check them using ns_capable() instead (if BPF
token is provided). See bpf_token_capable() for details.

Such setup means that BPF token in itself is not sufficient to grant BPF
functionality. User namespaced process has to *also* have necessary
combination of capabilities inside that user namespace. So while
previously CAP_BPF was useless when granted within user namespace, now
it gains a meaning and allows container managers and sys admins to have
a flexible control over which processes can and need to use BPF
functionality within the user namespace (i.e., container in practice).
And BPF FS delegation mount options and derived BPF tokens serve as
a per-container "flag" to grant overall ability to use bpf() (plus further
restrict on which parts of bpf() syscalls are treated as namespaced).

Note also, BPF_TOKEN_CREATE command itself requires ns_capable(CAP_BPF)
within the BPF FS owning user namespace, rounding up the ns_capable()
story of BPF token. Also creating BPF token in init user namespace is
currently not supported, given BPF token doesn't have any effect in init
user namespace anyways.

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Christian Brauner <brauner@kernel.org>
Link: https://lore.kernel.org/bpf/20240124022127.2379740-4-andrii@kernel.org

This work refactors and adds a lightweight extension ("tcx") to the tc BPF
ingress and egress data path side for allowing BPF program management based
on fds via bpf() syscall through the newly added generic multi-prog API.
The main goal behind this work which we also presented at LPC [0] last year
and a recent update at LSF/MM/BPF this year [3] is to support long-awaited
BPF link functionality for tc BPF programs, which allows for a model of safe
ownership and program detachment.

Given the rise in tc BPF users in cloud native environments, this becomes
necessary to avoid hard to debug incidents either through stale leftover
programs or 3rd party applications accidentally stepping on each others toes.
As a recap, a BPF link represents the attachment of a BPF program to a BPF
hook point. The BPF link holds a single reference to keep BPF program alive.
Moreover, hook points do not reference a BPF link, only the application's
fd or pinning does. A BPF link holds meta-data specific to attachment and
implements operations for link creation, (atomic) BPF program update,
detachment and introspection. The motivation for BPF links for tc BPF programs
is multi-fold, for example:

  - From Meta: "It's especially important for applications that are deployed
    fleet-wide and that don't "control" hosts they are deployed to. If such
    application crashes and no one notices and does anything about that, BPF
    program will keep running draining resources or even just, say, dropping
    packets. We at FB had outages due to such permanent BPF attachment
    semantics. With fd-based BPF link we are getting a framework, which allows
    safe, auto-detachable behavior by default, unless application explicitly
    opts in by pinning the BPF link." [1]

  - From Cilium-side the tc BPF programs we attach to host-facing veth devices
    and phys devices build the core datapath for Kubernetes Pods, and they
    implement forwarding, load-balancing, policy, EDT-management, etc, within
    BPF. Currently there is no concept of 'safe' ownership, e.g. we've recently
    experienced hard-to-debug issues in a user's staging environment where
    another Kubernetes application using tc BPF attached to the same prio/handle
    of cls_bpf, accidentally wiping all Cilium-based BPF programs from underneath
    it. The goal is to establish a clear/safe ownership model via links which
    cannot accidentally be overridden. [0,2]

BPF links for tc can co-exist with non-link attachments, and the semantics are
in line also with XDP links: BPF links cannot replace other BPF links, BPF
links cannot replace non-BPF links, non-BPF links cannot replace BPF links and
lastly only non-BPF links can replace non-BPF links. In case of Cilium, this
would solve mentioned issue of safe ownership model as 3rd party applications
would not be able to accidentally wipe Cilium programs, even if they are not
BPF link aware.

Earlier attempts [4] have tried to integrate BPF links into core tc machinery
to solve cls_bpf, which has been intrusive to the generic tc kernel API with
extensions only specific to cls_bpf and suboptimal/complex since cls_bpf could
be wiped from the qdisc also. Locking a tc BPF program in place this way, is
getting into layering hacks given the two object models are vastly different.

We instead implemented the tcx (tc 'express') layer which is an fd-based tc BPF
attach API, so that the BPF link implementation blends in naturally similar to
other link types which are fd-based and without the need for changing core tc
internal APIs. BPF programs for tc can then be successively migrated from classic
cls_bpf to the new tc BPF link without needing to change the program's source
code, just the BPF loader mechanics for attaching is sufficient.

For the current tc framework, there is no change in behavior with this change
and neither does this change touch on tc core kernel APIs. The gist of this
patch is that the ingress and egress hook have a lightweight, qdisc-less
extension for BPF to attach its tc BPF programs, in other words, a minimal
entry point for tc BPF. The name tcx has been suggested from discussion of
earlier revisions of this work as a good fit, and to more easily differ between
the classic cls_bpf attachment and the fd-based one.

For the ingress and egress tcx points, the device holds a cache-friendly array
with program pointers which is separated from control plane (slow-path) data.
Earlier versions of this work used priority to determine ordering and expression
of dependencies similar as with classic tc, but it was challenged that for
something more future-proof a better user experience is required. Hence this
resulted in the design and development of the generic attach/detach/query API
for multi-progs. See prior patch with its discussion on the API design. tcx is
the first user and later we plan to integrate also others, for example, one
candidate is multi-prog support for XDP which would benefit and have the same
'look and feel' from API perspective.

The goal with tcx is to have maximum compatibility to existing tc BPF programs,
so they don't need to be rewritten specifically. Compatibility to call into
classic tcf_classify() is also provided in order to allow successive migration
or both to cleanly co-exist where needed given its all one logical tc layer and
the tcx plus classic tc cls/act build one logical overall processing pipeline.

tcx supports the simplified return codes TCX_NEXT which is non-terminating (go
to next program) and terminating ones with TCX_PASS, TCX_DROP, TCX_REDIRECT.
The fd-based API is behind a static key, so that when unused the code is also
not entered. The struct tcx_entry's program array is currently static, but
could be made dynamic if necessary at a point in future. The a/b pair swap
design has been chosen so that for detachment there are no allocations which
otherwise could fail.

The work has been tested with tc-testing selftest suite which all passes, as
well as the tc BPF tests from the BPF CI, and also with Cilium's L4LB.

Thanks also to Nikolay Aleksandrov and Martin Lau for in-depth early reviews
of this work.

  [0] https://lpc.events/event/16/contributions/1353/
  [1] https://lore.kernel.org/bpf/CAEf4BzbokCJN33Nw_kg82sO=xppXnKWEncGTWCTB9vGCmLB6pw@mail.gmail.com
  [2] https://colocatedeventseu2023.sched.com/event/1Jo6O/tales-from-an-ebpf-programs-murder-mystery-hemanth-malla-guillaume-fournier-datadog
  [3] http://vger.kernel.org/bpfconf2023_material/tcx_meta_netdev_borkmann.pdf
  [4] https://lore.kernel.org/bpf/20210604063116.234316-1-memxor@gmail.com

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Jakub Kicinski <kuba@kernel.org>
Link: https://lore.kernel.org/r/20230719140858.13224-3-daniel@iogearbox.net
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

This adds a generic layer called bpf_mprog which can be reused by different
attachment layers to enable multi-program attachment and dependency resolution.
In-kernel users of the bpf_mprog don't need to care about the dependency
resolution internals, they can just consume it with few API calls.

The initial idea of having a generic API sparked out of discussion [0] from an
earlier revision of this work where tc's priority was reused and exposed via
BPF uapi as a way to coordinate dependencies among tc BPF programs, similar
as-is for classic tc BPF. The feedback was that priority provides a bad user
experience and is hard to use [1], e.g.:

  I cannot help but feel that priority logic copy-paste from old tc, netfilter
  and friends is done because "that's how things were done in the past". [...]
  Priority gets exposed everywhere in uapi all the way to bpftool when it's
  right there for users to understand. And that's the main problem with it.

  The user don't want to and don't need to be aware of it, but uapi forces them
  to pick the priority. [...] Your cover letter [0] example proves that in
  real life different service pick the same priority. They simply don't know
  any better. Priority is an unnecessary magic that apps _have_ to pick, so
  they just copy-paste and everyone ends up using the same.

The course of the discussion showed more and more the need for a generic,
reusable API where the "same look and feel" can be applied for various other
program types beyond just tc BPF, for example XDP today does not have multi-
program support in kernel, but also there was interest around this API for
improving management of cgroup program types. Such common multi-program
management concept is useful for BPF management daemons or user space BPF
applications coordinating internally about their attachments.

Both from Cilium and Meta side [2], we've collected the following requirements
for a generic attach/detach/query API for multi-progs which has been implemented
as part of this work:

  - Support prog-based attach/detach and link API
  - Dependency directives (can also be combined):
    - BPF_F_{BEFORE,AFTER} with relative_{fd,id} which can be {prog,link,none}
      - BPF_F_ID flag as {fd,id} toggle; the rationale for id is so that user
        space application does not need CAP_SYS_ADMIN to retrieve foreign fds
        via bpf_*_get_fd_by_id()
      - BPF_F_LINK flag as {prog,link} toggle
      - If relative_{fd,id} is none, then BPF_F_BEFORE will just prepend, and
        BPF_F_AFTER will just append for attaching
      - Enforced only at attach time
    - BPF_F_REPLACE with replace_bpf_fd which can be prog, links have their
      own infra for replacing their internal prog
    - If no flags are set, then it's default append behavior for attaching
  - Internal revision counter and optionally being able to pass expected_revision
  - User space application can query current state with revision, and pass it
    along for attachment to assert current state before doing updates
  - Query also gets extension for link_ids array and link_attach_flags:
    - prog_ids are always filled with program IDs
    - link_ids are filled with link IDs when link was used, otherwise 0
    - {prog,link}_attach_flags for holding {prog,link}-specific flags
  - Must be easy to integrate/reuse for in-kernel users

The uapi-side changes needed for supporting bpf_mprog are rather minimal,
consisting of the additions of the attachment flags, revision counter, and
expanding existing union with relative_{fd,id} member.

The bpf_mprog framework consists of an bpf_mprog_entry object which holds
an array of bpf_mprog_fp (fast-path structure). The bpf_mprog_cp (control-path
structure) is part of bpf_mprog_bundle. Both have been separated, so that
fast-path gets efficient packing of bpf_prog pointers for maximum cache
efficiency. Also, array has been chosen instead of linked list or other
structures to remove unnecessary indirections for a fast point-to-entry in
tc for BPF.

The bpf_mprog_entry comes as a pair via bpf_mprog_bundle so that in case of
updates the peer bpf_mprog_entry is populated and then just swapped which
avoids additional allocations that could otherwise fail, for example, in
detach case. bpf_mprog_{fp,cp} arrays are currently static, but they could
be converted to dynamic allocation if necessary at a point in future.
Locking is deferred to the in-kernel user of bpf_mprog, for example, in case
of tcx which uses this API in the next patch, it piggybacks on rtnl.

An extensive test suite for checking all aspects of this API for prog-based
attach/detach and link API comes as BPF selftests in this series.

Thanks also to Andrii Nakryiko for early API discussions wrt Meta's BPF prog
management.

  [0] https://lore.kernel.org/bpf/20221004231143.19190-1-daniel@iogearbox.net
  [1] https://lore.kernel.org/bpf/CAADnVQ+gEY3FjCR=+DmjDR4gp5bOYZUFJQXj4agKFHT9CQPZBw@mail.gmail.com
  [2] http://vger.kernel.org/bpfconf2023_material/tcx_meta_netdev_borkmann.pdf

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/r/20230719140858.13224-2-daniel@iogearbox.net
Signed-off-by: Alexei Starovoitov <ast@kernel.org>