selftests/bpf: Add socket filter attach test

This test verifies socket filter attachment functionality on architectures
supporting either BPF JIT compilation or the interpreter.

It specifically validates the fallback to interpreter behavior when JIT fails,
particularly targeting ARMv6 devices with the following configuration:
  # CONFIG_BPF_JIT_ALWAYS_ON is not set
  CONFIG_BPF_JIT_DEFAULT_ON=y

Signed-off-by: KaFai Wan <[email protected]>

Author: mannkafai

tools/testing/selftests/bpf/prog_tests/socket_filter.c

@@ -0,0 +1,124 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <test_progs.h>
+#include <sys/utsname.h>
+#include <uapi/linux/filter.h>
+#include "socket_filter.skel.h"
+
+static int duration;
+
+void do_test(void)
+{
+	/* the filter below is the tcpdump filter:
+	 * tcpdump "not ether host 3c37121a2b3c and not ether host 184ecbca2a3a \
+	 * and not ether host 14130b4d3f47 and not ether host f0f61cf440b7 \
+	 * and not ether host a84b4dedf471 and not ether host d022be17e1d7 \
+	 * and not ether host 5c497967208b and not ether host 706655784d5b"
+	 */
+	struct sock_filter code[] = {
+		{ 0x20,  0,  0, 0x00000008 },
+		{ 0x15,  0,  2, 0x121a2b3c },
+		{ 0x28,  0,  0, 0x00000006 },
+		{ 0x15, 60,  0, 0x00003c37 },
+		{ 0x20,  0,  0, 0x00000002 },
+		{ 0x15,  0,  2, 0x121a2b3c },
+		{ 0x28,  0,  0, 0x00000000 },
+		{ 0x15, 56,  0, 0x00003c37 },
+		{ 0x20,  0,  0, 0x00000008 },
+		{ 0x15,  0,  2, 0xcbca2a3a },
+		{ 0x28,  0,  0, 0x00000006 },
+		{ 0x15, 52,  0, 0x0000184e },
+		{ 0x20,  0,  0, 0x00000002 },
+		{ 0x15,  0,  2, 0xcbca2a3a },
+		{ 0x28,  0,  0, 0x00000000 },
+		{ 0x15, 48,  0, 0x0000184e },
+		{ 0x20,  0,  0, 0x00000008 },
+		{ 0x15,  0,  2, 0x0b4d3f47 },
+		{ 0x28,  0,  0, 0x00000006 },
+		{ 0x15, 44,  0, 0x00001413 },
+		{ 0x20,  0,  0, 0x00000002 },
+		{ 0x15,  0,  2, 0x0b4d3f47 },
+		{ 0x28,  0,  0, 0x00000000 },
+		{ 0x15, 40,  0, 0x00001413 },
+		{ 0x20,  0,  0, 0x00000008 },
+		{ 0x15,  0,  2, 0x1cf440b7 },
+		{ 0x28,  0,  0, 0x00000006 },
+		{ 0x15, 36,  0, 0x0000f0f6 },
+		{ 0x20,  0,  0, 0x00000002 },
+		{ 0x15,  0,  2, 0x1cf440b7 },
+		{ 0x28,  0,  0, 0x00000000 },
+		{ 0x15, 32,  0, 0x0000f0f6 },
+		{ 0x20,  0,  0, 0x00000008 },
+		{ 0x15,  0,  2, 0x4dedf471 },
+		{ 0x28,  0,  0, 0x00000006 },
+		{ 0x15, 28,  0, 0x0000a84b },
+		{ 0x20,  0,  0, 0x00000002 },
+		{ 0x15,  0,  2, 0x4dedf471 },
+		{ 0x28,  0,  0, 0x00000000 },
+		{ 0x15, 24,  0, 0x0000a84b },
+		{ 0x20,  0,  0, 0x00000008 },
+		{ 0x15,  0,  2, 0xbe17e1d7 },
+		{ 0x28,  0,  0, 0x00000006 },
+		{ 0x15, 20,  0, 0x0000d022 },
+		{ 0x20,  0,  0, 0x00000002 },
+		{ 0x15,  0,  2, 0xbe17e1d7 },
+		{ 0x28,  0,  0, 0x00000000 },
+		{ 0x15, 16,  0, 0x0000d022 },
+		{ 0x20,  0,  0, 0x00000008 },
+		{ 0x15,  0,  2, 0x7967208b },
+		{ 0x28,  0,  0, 0x00000006 },
+		{ 0x15, 12,  0, 0x00005c49 },
+		{ 0x20,  0,  0, 0x00000002 },
+		{ 0x15,  0,  2, 0x7967208b },
+		{ 0x28,  0,  0, 0x00000000 },
+		{ 0x15,  8,  0, 0x00005c49 },
+		{ 0x20,  0,  0, 0x00000008 },
+		{ 0x15,  0,  2, 0x55784d5b },
+		{ 0x28,  0,  0, 0x00000006 },
+		{ 0x15,  4,  0, 0x00007066 },
+		{ 0x20,  0,  0, 0x00000002 },
+		{ 0x15,  0,  3, 0x55784d5b },
+		{ 0x28,  0,  0, 0x00000000 },
+		{ 0x15,  0,  1, 0x00007066 },
+		{ 0x06,  0,  0, 0x00000000 },
+		{ 0x06,  0,  0, 0x00040000 },
+	};
+	struct sock_fprog bpf = {
+		.len = ARRAY_SIZE(code),
+		.filter = code,
+	};
+	int ret, sock = 0;
+
+	sock = socket(PF_PACKET, SOCK_RAW, htons(ETH_P_ALL));
+	if (CHECK(sock < 0, "create socket", "errno %d\n", errno))
+		return;
+
+	ret = setsockopt(sock, SOL_SOCKET, SO_ATTACH_FILTER, &bpf, sizeof(bpf));
+	CHECK(ret < 0, "attach filter", "errno %d\n", errno);
+
+	close(sock);
+}
+
+void test_socket_filter(void)
+{
+	struct socket_filter *skel;
+	struct utsname uts;
+	int err;
+
+	err = uname(&uts);
+	if (err < 0)
+		return;
+
+	skel = socket_filter__open_and_load();
+	if (!ASSERT_OK_PTR(skel, "skel_open"))
+		return;
+
+	/* The filter JIT fails on armv6 */
+	if (strncmp(uts.machine, "armv6", strlen("armv6")) == 0 &&
+	    skel->kconfig->CONFIG_BPF_JIT_ALWAYS_ON)
+		test__skip();
+	else
+		do_test();
+
+	socket_filter__destroy(skel);
+}

tools/testing/selftests/bpf/progs/socket_filter.c

@@ -0,0 +1,16 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include "vmlinux.h"
+#include <bpf/bpf_helpers.h>
+
+char _license[] SEC("license") = "GPL";
+
+extern bool CONFIG_BPF_JIT_ALWAYS_ON __kconfig __weak;
+
+/* This function is here to have CONFIG_BPF_JIT_ALWAYS_ON
+ * used and added to object BTF.
+ */
+int unused(void)
+{
+	return CONFIG_BPF_JIT_ALWAYS_ON ? 0 : 1;
+}