Merge branch 'bpf: Support calling kernel function'

Martin KaFai says:

====================

This series adds support to allow bpf program calling kernel function.

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.

Please see individual patch for details.

v2:
- Patch 2 in v1 is removed.  No need to support extern func in kernel.
  Changed libbpf to adjust the .ksyms datasec for extern func
  in patch 11. (Andrii)
- Name change: btf_check_func_arg_match() and btf_check_subprog_arg_match()
  in patch 2. (Andrii)
- Always set unreliable on any error in patch 2 since it does not
  matter. (Andrii)
- s/kern_func/kfunc/ and s/descriptor/desc/ in this set. (Andrii)
- Remove some unnecessary changes in disasm.h and disasm.c
  in patch 3.  In particular, no need to change the function
  signature in bpf_insn_revmap_call_t.  Also, removed the changes
  in print_bpf_insn().
- Fixed an issue in check_kfunc_call() when the calling kernel function
  returns a pointer in patch 3.  Added a selftest.
- Adjusted the verifier selftests due to the changes in the verifier log
  in patch 3.
- Fixed a comparison issue in kfunc_desc_cmp_by_imm() in patch 3. (Andrii)
- Name change: is_ldimm64_insn(),
  new helper: is_call_insn() in patch 10 (Andrii)
- Move btf_func_linkage() from btf.h to libbpf.c in patch 11. (Andrii)
- Fixed the linker error when CONFIG_BPF_SYSCALL is not defined.
  Moved the check_kfunc_call from filter.c to test_run.c in patch 14.
  (kernel test robot)
====================

Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 59 insertions, 0 deletions

diff --git a/tools/testing/selftests/bpf/prog_tests/kfunc_call.c b/tools/testing/selftests/bpf/prog_tests/kfunc_call.c
new file mode 100644
index 000000000000..7fc0951ee75f
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/kfunc_call.c
@@ -0,0 +1,59 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2021 Facebook */
+#include <test_progs.h>
+#include <network_helpers.h>
+#include "kfunc_call_test.skel.h"
+#include "kfunc_call_test_subprog.skel.h"
+
+static void test_main(void)
+{
+	struct kfunc_call_test *skel;
+	int prog_fd, retval, err;
+
+	skel = kfunc_call_test__open_and_load();
+	if (!ASSERT_OK_PTR(skel, "skel"))
+		return;
+
+	prog_fd = bpf_program__fd(skel->progs.kfunc_call_test1);
+	err = bpf_prog_test_run(prog_fd, 1, &pkt_v4, sizeof(pkt_v4),
+				NULL, NULL, (__u32 *)&retval, NULL);
+	ASSERT_OK(err, "bpf_prog_test_run(test1)");
+	ASSERT_EQ(retval, 12, "test1-retval");
+
+	prog_fd = bpf_program__fd(skel->progs.kfunc_call_test2);
+	err = bpf_prog_test_run(prog_fd, 1, &pkt_v4, sizeof(pkt_v4),
+				NULL, NULL, (__u32 *)&retval, NULL);
+	ASSERT_OK(err, "bpf_prog_test_run(test2)");
+	ASSERT_EQ(retval, 3, "test2-retval");
+
+	kfunc_call_test__destroy(skel);
+}
+
+static void test_subprog(void)
+{
+	struct kfunc_call_test_subprog *skel;
+	int prog_fd, retval, err;
+
+	skel = kfunc_call_test_subprog__open_and_load();
+	if (!ASSERT_OK_PTR(skel, "skel"))
+		return;
+
+	prog_fd = bpf_program__fd(skel->progs.kfunc_call_test1);
+	err = bpf_prog_test_run(prog_fd, 1, &pkt_v4, sizeof(pkt_v4),
+				NULL, NULL, (__u32 *)&retval, NULL);
+	ASSERT_OK(err, "bpf_prog_test_run(test1)");
+	ASSERT_EQ(retval, 10, "test1-retval");
+	ASSERT_NEQ(skel->data->active_res, -1, "active_res");
+	ASSERT_EQ(skel->data->sk_state, BPF_TCP_CLOSE, "sk_state");
+
+	kfunc_call_test_subprog__destroy(skel);
+}
+
+void test_kfunc_call(void)
+{
+	if (test__start_subtest("main"))
+		test_main();
+
+	if (test__start_subtest("subprog"))
+		test_subprog();
+}