Vinicius Costa Gomes reported [0] that build fails when
CONFIG_DEBUG_INFO_BTF is enabled and CONFIG_BPF_SYSCALL is disabled.
This leads to btf.c not being compiled, and then no symbol being present
in vmlinux for the declarations in btf.h. Since BTF is not useful
without enabling BPF subsystem, disallow this combination.

However, theoretically disabling both now could still fail, as the
symbol for kfunc_btf_id_list variables is not available. This isn't a
problem as the compiler usually optimizes the whole register/unregister
call, but at lower optimization levels it can fail the build in linking
stage.

Fix that by adding dummy variables so that modules taking address of
them still work, but the whole thing is a noop.

  [0]: https://lore.kernel.org/bpf/20211110205418.332403-1-vinicius.gomes@intel.com

Fixes: 14f267d95fe4 ("bpf: btf: Introduce helpers for dynamic BTF set registration")
Reported-by: Vinicius Costa Gomes <vinicius.gomes@intel.com>
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Song Liu <songliubraving@fb.com>
Link: https://lore.kernel.org/bpf/20211122144742.477787-2-memxor@gmail.com

This adds selftests that tests the success and failure path for modules
kfuncs (in presence of invalid kfunc calls) for both libbpf and
gen_loader. It also adds a prog_test kfunc_btf_id_list so that we can
add module BTF ID set from bpf_testmod.

This also introduces  a couple of test cases to verifier selftests for
validating whether we get an error or not depending on if invalid kfunc
call remains after elimination of unreachable instructions.

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20211002011757.311265-10-memxor@gmail.com

This commit moves BTF ID lookup into the newly added registration
helper, in a way that the bbr, cubic, and dctcp implementation set up
their sets in the bpf_tcp_ca kfunc_btf_set list, while the ones not
dependent on modules are looked up from the wrapper function.

This lifts the restriction for them to be compiled as built in objects,
and can be loaded as modules if required. Also modify Makefile.modfinal
to call resolve_btfids for each module.

Note that since kernel kfunc_ids never overlap with module kfunc_ids, we
only match the owner for module btf id sets.

See following commits for background on use of:

 CONFIG_X86 ifdef:
 569c484f9995 (bpf: Limit static tcp-cc functions in the .BTF_ids list to x86)

 CONFIG_DYNAMIC_FTRACE ifdef:
 7aae231ac93b (bpf: tcp: Limit calling some tcp cc functions to CONFIG_DYNAMIC_FTRACE)

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20211002011757.311265-6-memxor@gmail.com

This adds helpers for registering btf_id_set from modules and the
bpf_check_mod_kfunc_call callback that can be used to look them up.

With in kernel sets, the way this is supposed to work is, in kernel
callback looks up within the in-kernel kfunc whitelist, and then defers
to the dynamic BTF set lookup if it doesn't find the BTF id. If there is
no in-kernel BTF id set, this callback can be used directly.

Also fix includes for btf.h and bpfptr.h so that they can included in
isolation. This is in preparation for their usage in tcp_bbr, tcp_cubic
and tcp_dctcp modules in the next patch.

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20211002011757.311265-4-memxor@gmail.com

Restrict bpf timers to array, hash (both preallocated and kmalloced), and
lru map types. The per-cpu maps with timers don't make sense, since 'struct
bpf_timer' is a part of map value. bpf timers in per-cpu maps would mean that
the number of timers depends on number of possible cpus and timers would not be
accessible from all cpus. lpm map support can be added in the future.
The timers in inner maps are supported.

The bpf_map_update/delete_elem() helpers and sys_bpf commands cancel and free
bpf_timer in a given map element.

Similar to 'struct bpf_spin_lock' BTF is required and it is used to validate
that map element indeed contains 'struct bpf_timer'.

Make check_and_init_map_value() init both bpf_spin_lock and bpf_timer when
map element data is reused in preallocated htab and lru maps.

Teach copy_map_value() to support both bpf_spin_lock and bpf_timer in a single
map element. There could be one of each, but not more than one. Due to 'one
bpf_timer in one element' restriction do not support timers in global data,
since global data is a map of single element, but from bpf program side it's
seen as many global variables and restriction of single global timer would be
odd. The sys_bpf map_freeze and sys_mmap syscalls are not allowed on maps with
timers, since user space could have corrupted mmap element and crashed the
kernel. The maps with timers cannot be readonly. Due to these restrictions
search for bpf_timer in datasec BTF in case it was placed in the global data to
report clear error.

The previous patch allowed 'struct bpf_timer' as a first field in a map
element only. Relax this restriction.

Refactor lru map to s/bpf_lru_push_free/htab_lru_push_free/ to cancel and free
the timer when lru map deletes an element as a part of it eviction algorithm.

Make sure that bpf program cannot access 'struct bpf_timer' via direct load/store.
The timer operation are done through helpers only.
This is similar to 'struct bpf_spin_lock'.

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Yonghong Song <yhs@fb.com>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Toke Høiland-Jørgensen <toke@redhat.com>
Link: https://lore.kernel.org/bpf/20210715005417.78572-5-alexei.starovoitov@gmail.com

Similar to prog_load make btf_load command to be availble to
bpf_prog_type_syscall program.

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20210514003623.28033-7-alexei.starovoitov@gmail.com

This patch adds support to BPF verifier to allow bpf program calling
kernel function directly.

The use case included in this set is to allow bpf-tcp-cc to directly
call some tcp-cc helper functions (e.g. "tcp_cong_avoid_ai()").  Those
functions have already been used by some kernel tcp-cc implementations.

This set will also allow the bpf-tcp-cc program to directly call the
kernel tcp-cc implementation,  For example, a bpf_dctcp may only want to
implement its own dctcp_cwnd_event() and reuse other dctcp_*() directly
from the kernel tcp_dctcp.c instead of reimplementing (or
copy-and-pasting) them.

The tcp-cc kernel functions mentioned above will be white listed
for the struct_ops bpf-tcp-cc programs to use in a later patch.
The white listed functions are not bounded to a fixed ABI contract.
Those functions have already been used by the existing kernel tcp-cc.
If any of them has changed, both in-tree and out-of-tree kernel tcp-cc
implementations have to be changed.  The same goes for the struct_ops
bpf-tcp-cc programs which have to be adjusted accordingly.

This patch is to make the required changes in the bpf verifier.

First change is in btf.c, it adds a case in "btf_check_func_arg_match()".
When the passed in "btf->kernel_btf == true", it means matching the
verifier regs' states with a kernel function.  This will handle the
PTR_TO_BTF_ID reg.  It also maps PTR_TO_SOCK_COMMON, PTR_TO_SOCKET,
and PTR_TO_TCP_SOCK to its kernel's btf_id.

In the later libbpf patch, the insn calling a kernel function will
look like:

insn->code == (BPF_JMP | BPF_CALL)
insn->src_reg == BPF_PSEUDO_KFUNC_CALL /* <- new in this patch */
insn->imm == func_btf_id /* btf_id of the running kernel */

[ For the future calling function-in-kernel-module support, an array
  of module btf_fds can be passed at the load time and insn->off
  can be used to index into this array. ]

At the early stage of verifier, the verifier will collect all kernel
function calls into "struct bpf_kfunc_desc".  Those
descriptors are stored in "prog->aux->kfunc_tab" and will
be available to the JIT.  Since this "add" operation is similar
to the current "add_subprog()" and looking for the same insn->code,
they are done together in the new "add_subprog_and_kfunc()".

In the "do_check()" stage, the new "check_kfunc_call()" is added
to verify the kernel function call instruction:
1. Ensure the kernel function can be used by a particular BPF_PROG_TYPE.
   A new bpf_verifier_ops "check_kfunc_call" is added to do that.
   The bpf-tcp-cc struct_ops program will implement this function in
   a later patch.
2. Call "btf_check_kfunc_args_match()" to ensure the regs can be
   used as the args of a kernel function.
3. Mark the regs' type, subreg_def, and zext_dst.

At the later do_misc_fixups() stage, the new fixup_kfunc_call()
will replace the insn->imm with the function address (relative
to __bpf_call_base).  If needed, the jit can find the btf_func_model
by calling the new bpf_jit_find_kfunc_model(prog, insn).
With the imm set to the function address, "bpftool prog dump xlated"
will be able to display the kernel function calls the same way as
it displays other bpf helper calls.

gpl_compatible program is required to call kernel function.

This feature currently requires JIT.

The verifier selftests are adjusted because of the changes in
the verbose log in add_subprog_and_kfunc().

Signed-off-by: Martin KaFai Lau <kafai@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20210325015142.1544736-1-kafai@fb.com

This patch moved the subprog specific logic from
btf_check_func_arg_match() to the new btf_check_subprog_arg_match().
The core logic is left in btf_check_func_arg_match() which
will be reused later to check the kernel function call.

The "if (!btf_type_is_ptr(t))" is checked first to improve the
indentation which will be useful for a later patch.

Some of the "btf_kind_str[]" usages is replaced with the shortcut
"btf_type_str(t)".

Signed-off-by: Martin KaFai Lau <kafai@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20210325015136.1544504-1-kafai@fb.com

The selftest failed to compile with clang-built bpf-next.
Adding LLVM=1 to your vmlinux and selftest build will use clang.
The error message is:
  progs/test_sk_storage_tracing.c:38:18: error: use of undeclared identifier 'BPF_TCP_CLOSE'
          if (newstate == BPF_TCP_CLOSE)
                          ^
  1 error generated.
  make: *** [Makefile:423: /bpf-next/tools/testing/selftests/bpf/test_sk_storage_tracing.o] Error 1

The reason for the failure is that BPF_TCP_CLOSE, a value of
an anonymous enum defined in uapi bpf.h, is not defined in
vmlinux.h. gcc does not have this problem. Since vmlinux.h
is derived from BTF which is derived from vmlinux DWARF,
that means gcc-produced vmlinux DWARF has BPF_TCP_CLOSE
while llvm-produced vmlinux DWARF does not have.

BPF_TCP_CLOSE is referenced in net/ipv4/tcp.c as
  BUILD_BUG_ON((int)BPF_TCP_CLOSE != (int)TCP_CLOSE);
The following test mimics the above BUILD_BUG_ON, preprocessed
with clang compiler, and shows gcc DWARF contains BPF_TCP_CLOSE while
llvm DWARF does not.

  $ cat t.c
  enum {
    BPF_TCP_ESTABLISHED = 1,
    BPF_TCP_CLOSE = 7,
  };
  enum {
    TCP_ESTABLISHED = 1,
    TCP_CLOSE = 7,
  };

  int test() {
    do {
      extern void __compiletime_assert_767(void) ;
      if ((int)BPF_TCP_CLOSE != (int)TCP_CLOSE) __compiletime_assert_767();
    } while (0);
    return 0;
  }
  $ clang t.c -O2 -c -g && llvm-dwarfdump t.o | grep BPF_TCP_CLOSE
  $ gcc t.c -O2 -c -g && llvm-dwarfdump t.o | grep BPF_TCP_CLOSE
                    DW_AT_name    ("BPF_TCP_CLOSE")

Further checking clang code find clang actually tried to
evaluate condition at compile time. If it is definitely
true/false, it will perform optimization and the whole if condition
will be removed before generating IR/debuginfo.

This patch explicited add an expression after the
above mentioned BUILD_BUG_ON in net/ipv4/tcp.c like
  (void)BPF_TCP_ESTABLISHED
to enable generation of debuginfo for the anonymous
enum which also includes BPF_TCP_CLOSE.

Signed-off-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20210317174132.589276-1-yhs@fb.com

Add support for directly accessing kernel module variables from BPF programs
using special ldimm64 instructions. This functionality builds upon vmlinux
ksym support, but extends ldimm64 with src_reg=BPF_PSEUDO_BTF_ID to allow
specifying kernel module BTF's FD in insn[1].imm field.

During BPF program load time, verifier will resolve FD to BTF object and will
take reference on BTF object itself and, for module BTFs, corresponding module
as well, to make sure it won't be unloaded from under running BPF program. The
mechanism used is similar to how bpf_prog keeps track of used bpf_maps.

One interesting change is also in how per-CPU variable is determined. The
logic is to find .data..percpu data section in provided BTF, but both vmlinux
and module each have their own .data..percpu entries in BTF. So for module's
case, the search for DATASEC record needs to look at only module's added BTF
types. This is implemented with custom search function.

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Yonghong Song <yhs@fb.com>
Acked-by: Hao Luo <haoluo@google.com>
Link: https://lore.kernel.org/bpf/20210112075520.4103414-6-andrii@kernel.org