[PATCH bpf-next v3 5/5] selftests/bpf: Test gen loader attach

[Mahe Tardy <mahe.tardy@gmail.com>]

Tests that nothing changes when only loading without attach, verifies
that unsupported program types return an error, and check that all
tracing program types successfully generate loader attach prog.

Then actually checks execution of the generated loader attach for two
LSM progs, verifying the links are correctly loading the appropriate
programs and that autoload=false and autoattach=false disable it.
Finally, checks that if one program out of many fails to attach, the
cleanup with detach is done correctly.

Signed-off-by: Mahe Tardy <mahe.tardy@gmail.com>
---
 .../bpf/prog_tests/gen_loader_attach.c        | 229 ++++++++++++++++++
 .../selftests/bpf/progs/gen_loader_attach.c   |  48 ++++
 2 files changed, 277 insertions(+)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/gen_loader_attach.c
 create mode 100644 tools/testing/selftests/bpf/progs/gen_loader_attach.c

diff --git a/tools/testing/selftests/bpf/prog_tests/gen_loader_attach.c b/tools/testing/selftests/bpf/prog_tests/gen_loader_attach.c
new file mode 100644
index 000000000000..1277709d7ef2
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/gen_loader_attach.c
@@ -0,0 +1,229 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2026 Isovalent */
+#include <test_progs.h>
+#include <dirent.h>
+#include <bpf/skel_internal.h>
+
+#define NR_PROGS 7
+
+enum execution_case {
+	ATTACH,
+	NO_AUTOLOAD,
+	NO_AUTOATTACH,
+	ROLLBACK,
+};
+
+static int link_create_attr_offset(const struct gen_loader_opts *opts, int index)
+{
+	const struct bpf_insn *insns = (const void *)opts->insns;
+	int i, count = opts->insns_sz / sizeof(*insns);
+
+	for (i = 4; i < count; i++) {
+		if (insns[i].code != (BPF_JMP | BPF_CALL) ||
+		    insns[i].imm != BPF_FUNC_sys_bpf ||
+		    insns[i - 4].code != (BPF_ALU64 | BPF_MOV | BPF_K) ||
+		    insns[i - 4].dst_reg != BPF_REG_1 ||
+		    insns[i - 4].imm != BPF_LINK_CREATE)
+			continue;
+		if (!index--)
+			return insns[i - 2].imm;
+	}
+	return -1;
+}
+
+static struct bpf_object *generate(struct gen_loader_opts *opts, enum execution_case test)
+{
+	struct bpf_program *prog;
+	struct bpf_object *obj;
+
+	obj = bpf_object__open_file("gen_loader_attach.bpf.o", NULL);
+	if (!ASSERT_OK_PTR(obj, "open"))
+		return NULL;
+	prog = bpf_object__find_program_by_name(obj, "lsm_open");
+	bpf_program__set_autoload(prog, test != NO_AUTOLOAD);
+	bpf_program__set_autoattach(prog, test != NO_AUTOATTACH);
+	if (!ASSERT_OK(bpf_object__gen_loader(obj, opts), "gen_loader") ||
+	    !ASSERT_OK(bpf_object__load(obj), "generate"))
+		goto err_out;
+	return obj;
+
+err_out:
+	bpf_object__close(obj);
+	return NULL;
+}
+
+static void check_load_only(void)
+{
+	LIBBPF_OPTS(gen_loader_opts, opts);
+	struct bpf_object *obj;
+
+	obj = generate(&opts, ATTACH);
+	if (!obj)
+		return;
+	ASSERT_EQ(link_create_attr_offset(&opts, 0), -1, "no_link_create");
+	bpf_object__close(obj);
+}
+
+static void check_unsupported(void)
+{
+	LIBBPF_OPTS(gen_loader_opts, opts, .gen_attach = true);
+	struct bpf_program *prog;
+	struct bpf_object *obj;
+
+	obj = bpf_object__open_file("gen_loader_attach.bpf.o", NULL);
+	if (!ASSERT_OK_PTR(obj, "open"))
+		return;
+	prog = bpf_object__find_program_by_name(obj, "socket");
+	bpf_program__set_autoload(prog, true);
+	if (ASSERT_OK(bpf_object__gen_loader(obj, &opts), "gen_loader"))
+		ASSERT_EQ(bpf_object__load(obj), -EOPNOTSUPP, "unsupported_attach");
+	bpf_object__close(obj);
+}
+
+static void check_tracing_generation(void)
+{
+	LIBBPF_OPTS(gen_loader_opts, opts, .gen_attach = true);
+	struct bpf_program *prog;
+	struct bpf_object *obj;
+	int index = 0;
+
+	obj = bpf_object__open_file("gen_loader_attach.bpf.o", NULL);
+	if (!ASSERT_OK_PTR(obj, "open"))
+		return;
+	bpf_object__for_each_program(prog, obj)
+		bpf_program__set_autoload(prog, bpf_program__type(prog) == BPF_PROG_TYPE_TRACING);
+	if (!ASSERT_OK(bpf_object__gen_loader(obj, &opts), "gen_loader") ||
+	    !ASSERT_OK(bpf_object__load(obj), "generate"))
+		goto out;
+	bpf_object__for_each_program(prog, obj) {
+		const union bpf_attr *attr;
+		int off;
+
+		if (!bpf_program__autoload(prog))
+			continue;
+		off = link_create_attr_offset(&opts, index++);
+		if (!ASSERT_GE(off, 0, bpf_program__name(prog)))
+			goto out;
+		attr = (const void *)(opts.data + off);
+		ASSERT_EQ(attr->link_create.attach_type,
+			  bpf_program__expected_attach_type(prog), bpf_program__name(prog));
+	}
+	ASSERT_EQ(link_create_attr_offset(&opts, index), -1, "link_count");
+out:
+	bpf_object__close(obj);
+}
+
+static int count_fds(void)
+{
+	struct dirent *entry;
+	int count = 0;
+	DIR *dir;
+
+	dir = opendir("/proc/self/fd");
+	if (!dir)
+		return -errno;
+	while ((entry = readdir(dir)))
+		if (entry->d_name[0] != '.')
+			count++;
+	closedir(dir);
+	return count;
+}
+
+static void check_execution(enum execution_case test)
+{
+	LIBBPF_OPTS(gen_loader_opts, gen, .gen_attach = true);
+	struct {
+		struct bpf_loader_ctx ctx;
+		struct bpf_prog_desc progs[NR_PROGS];
+		struct bpf_link_desc links[NR_PROGS];
+	} ctx = { .ctx.sz = sizeof(ctx) };
+	struct bpf_load_and_run_opts run = { .ctx = &ctx.ctx };
+	struct bpf_object *obj;
+	int i, off, err, before;
+
+	obj = generate(&gen, test);
+	if (!obj)
+		return;
+	run.insns = gen.insns;
+	run.insns_sz = gen.insns_sz;
+	run.data = gen.data;
+	run.data_sz = gen.data_sz;
+
+	if (test == ROLLBACK) {
+		off = link_create_attr_offset(&gen, 1);
+		if (!ASSERT_GE(off, 0, "second_link_attr"))
+			goto out;
+		/* Force the second attachment to fail after the first succeeded. */
+		((union bpf_attr *)(gen.data + off))->link_create.attach_type = BPF_TRACE_FENTRY;
+
+		before = count_fds();
+		if (!ASSERT_GE(before, 0, "count_fds"))
+			goto out;
+		ASSERT_EQ(bpf_load_and_run(&run), -EINVAL, "second_attach_failed");
+		ASSERT_EQ(count_fds(), before, "rollback_fds");
+		goto out;
+	}
+
+	err = bpf_load_and_run(&run);
+	if (!ASSERT_OK(err, "run_loader"))
+		goto out;
+
+	for (i = 0; i < NR_PROGS; i++) {
+		struct bpf_link_info link = {};
+		struct bpf_prog_info prog = {};
+		__u32 size;
+
+		/*
+		 * Only the first two programs load by default; NO_AUTOLOAD also
+		 * skips the first. NO_AUTOATTACH must still return its program FD.
+		 */
+		if (i >= 2 || (!i && test == NO_AUTOLOAD)) {
+			ASSERT_EQ(ctx.progs[i].prog_fd, 0, "skipped_program");
+		} else {
+			size = sizeof(prog);
+			if (!ASSERT_GT(ctx.progs[i].prog_fd, 0, "program_fd") ||
+			    !ASSERT_OK(bpf_prog_get_info_by_fd(ctx.progs[i].prog_fd, &prog, &size),
+				       "prog_info"))
+				continue;
+		}
+
+		/*
+		 * Unloaded programs have no link. NO_AUTOATTACH also leaves the
+		 * first program's link slot zero, even though its program is loaded.
+		 */
+		if (i >= 2 || (!i && (test == NO_AUTOLOAD || test == NO_AUTOATTACH))) {
+			ASSERT_EQ(ctx.links[i].link_fd, 0, "skipped_link");
+			continue;
+		}
+		/* Verify the link references the corresponding loaded program. */
+		size = sizeof(link);
+		if (!ASSERT_OK(bpf_link_get_info_by_fd(ctx.links[i].link_fd, &link, &size),
+			       "link_info"))
+			continue;
+		ASSERT_EQ(link.prog_id, prog.id, "attached_program");
+	}
+out:
+	for (i = 0; i < NR_PROGS; i++) {
+		skel_closenz(ctx.links[i].link_fd);
+		skel_closenz(ctx.progs[i].prog_fd);
+	}
+	bpf_object__close(obj);
+}
+
+void test_gen_loader_attach(void)
+{
+	if (test__start_subtest("load_only"))
+		check_load_only();
+	if (test__start_subtest("unsupported"))
+		check_unsupported();
+	if (test__start_subtest("tracing"))
+		check_tracing_generation();
+	if (test__start_subtest("execute"))
+		check_execution(ATTACH);
+	if (test__start_subtest("execute_no_autoload"))
+		check_execution(NO_AUTOLOAD);
+	if (test__start_subtest("execute_no_autoattach"))
+		check_execution(NO_AUTOATTACH);
+	if (test__start_subtest("rollback"))
+		check_execution(ROLLBACK);
+}
diff --git a/tools/testing/selftests/bpf/progs/gen_loader_attach.c b/tools/testing/selftests/bpf/progs/gen_loader_attach.c
new file mode 100644
index 000000000000..9a38fe4ac7bb
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/gen_loader_attach.c
@@ -0,0 +1,48 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2026 Isovalent */
+#include "vmlinux.h"
+#include <bpf/bpf_helpers.h>
+
+SEC("lsm/file_open")
+int lsm_open(void *ctx)
+{
+	return 0;
+}
+
+SEC("lsm/file_permission")
+int lsm_perm(void *ctx)
+{
+	return 0;
+}
+
+SEC("?socket")
+int socket(void *ctx)
+{
+	return 0;
+}
+
+SEC("?fentry/security_inode_getattr")
+int fentry(void *ctx)
+{
+	return 0;
+}
+
+SEC("?fexit/security_inode_getattr")
+int fexit(void *ctx)
+{
+	return 0;
+}
+
+SEC("?fmod_ret/security_inode_getattr")
+int fmod_ret(void *ctx)
+{
+	return 0;
+}
+
+SEC("?tp_btf/sys_enter")
+int tp_btf(void *ctx)
+{
+	return 0;
+}
+
+char _license[] SEC("license") = "GPL";
--
2.43.0