[RFC PATCH bpf-next 4/4] selftests/bpf: bpf_panic selftest

[Artem Savkov]

Add a selftest for bpf_panic() checking that the program will only load
if all the prerequisites are met.

Signed-off-by: Artem Savkov <asavkov@xxxxxxxxxx>
---
 .../selftests/bpf/prog_tests/bpf_panic.c      | 144 ++++++++++++++++++
 1 file changed, 144 insertions(+)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/bpf_panic.c

diff --git a/tools/testing/selftests/bpf/prog_tests/bpf_panic.c b/tools/testing/selftests/bpf/prog_tests/bpf_panic.c
new file mode 100644
index 000000000000..9d008c0a5140
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/bpf_panic.c
@@ -0,0 +1,144 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2022 Red Hat, Inc. */
+
+#include <test_progs.h>
+#include <bpf/btf.h>
+
+#include "cap_helpers.h"
+
+static int sysctl_get(const char *sysctl_path, char *old_val)
+{
+	int ret = 0;
+	FILE *fp;
+
+	fp = fopen(sysctl_path, "r");
+	if (!fp)
+		return -errno;
+
+	if (fscanf(fp, "%s", old_val) <= 0)
+		ret = -ENOENT;
+
+	fclose(fp);
+
+	return ret;
+}
+
+static int sysctl_set(const char *sysctl_path, const char *new_val)
+{
+	int ret = 0;
+	FILE *fp;
+
+	fp = fopen(sysctl_path, "w");
+	if (!fp)
+		return -errno;
+
+	if (fprintf(fp, "%s", new_val) < 0)
+		ret = -errno;
+
+	fclose(fp);
+
+	return ret;
+}
+
+static char bpf_vlog[UINT_MAX >> 8];
+
+static void test_bpf_panic_conditions(void)
+{
+	int fd_prog;
+	int map_fd;
+	struct bpf_insn prog_insns[] = {
+		BPF_LD_MAP_VALUE(BPF_REG_1, 0, 0),
+		BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, 0, 0, BPF_FUNC_panic),
+		BPF_MOV64_IMM(BPF_REG_0, 0),
+		BPF_EXIT_INSN(),
+	};
+	const size_t prog_insn_cnt = sizeof(prog_insns) / sizeof(struct bpf_insn);
+	LIBBPF_OPTS(bpf_prog_load_opts, load_opts);
+	LIBBPF_OPTS(bpf_map_create_opts, map_create_opts);
+	int attach_btf_id;
+	__u64 save_caps = 0;
+
+	if (!ASSERT_OK(sysctl_set("/proc/sys/kernel/destructive_bpf_enabled",
+			 "1"), "set destructive_bpf_enabled"))
+		return;
+
+	load_opts.log_level = 1;
+	load_opts.log_buf = bpf_vlog;
+	load_opts.log_size = sizeof(bpf_vlog);
+	load_opts.expected_attach_type = BPF_TRACE_FENTRY;
+
+	attach_btf_id = libbpf_find_vmlinux_btf_id("dentry_open", load_opts.expected_attach_type);
+	if (!ASSERT_GE(attach_btf_id, 0, "attach_btf_id"))
+		return;
+
+	load_opts.attach_btf_id = attach_btf_id;
+
+	map_create_opts.map_flags = BPF_F_RDONLY_PROG;
+	map_fd = bpf_map_create(BPF_MAP_TYPE_ARRAY, NULL, 4, 8, 1, &map_create_opts);
+	if (!ASSERT_GE(map_fd, 0, "bpf_map_create"))
+		return;
+	ASSERT_OK(bpf_map_freeze(map_fd), "bpf_map_freeze");
+
+	prog_insns[0].imm = map_fd;
+
+	fd_prog = bpf_prog_load(BPF_PROG_TYPE_TRACING, "bpf_panic", "GPL", prog_insns, prog_insn_cnt, &load_opts);
+
+	if (ASSERT_EQ(fd_prog, -EACCES, "BPF_F_DESTRUCTIVE required")) {
+		if (!ASSERT_OK_PTR(
+				strstr(bpf_vlog, "require BPF_F_DESTRUCTIVE"),
+				"BPF_F_DESTRUCTIVE verifier log")) {
+			printf("verifier log:\n%s\n", bpf_vlog);
+		}
+	}
+
+	load_opts.prog_flags = BPF_F_DESTRUCTIVE;
+	fd_prog = bpf_prog_load(BPF_PROG_TYPE_TRACING, "bpf_panic", "GPL", prog_insns, prog_insn_cnt, &load_opts);
+
+	if (ASSERT_GE(fd_prog, 0, "successful load")) {
+		close(fd_prog);
+	} else {
+		printf("verifier log:\n%s\n", bpf_vlog);
+	}
+
+
+	if (ASSERT_OK(cap_disable_effective(1ULL << CAP_SYS_BOOT, &save_caps), "disable caps")) {
+		fd_prog = bpf_prog_load(BPF_PROG_TYPE_TRACING, "bpf_panic", "GPL", prog_insns, prog_insn_cnt, &load_opts);
+		ASSERT_EQ(fd_prog, -EINVAL, "CAP_SYS_BOOT required");
+		if (!ASSERT_OK_PTR(
+				strstr(bpf_vlog, "unknown func bpf_panic"),
+				"CAP_SYS_BOOT verifier log")) {
+			printf("verifier log:\n%s\n", bpf_vlog);
+		}
+		cap_enable_effective(save_caps, NULL);
+	}
+
+	if (ASSERT_OK(sysctl_set("/proc/sys/kernel/destructive_bpf_enabled",
+			 "0"), "unset destructive_bpf_enabled")) {
+		fd_prog = bpf_prog_load(BPF_PROG_TYPE_TRACING, "bpf_panic", "GPL", prog_insns, prog_insn_cnt, &load_opts);
+		ASSERT_EQ(fd_prog, -EINVAL, "!destructive_bpf_enabled");
+		if (!ASSERT_OK_PTR(
+				strstr(bpf_vlog, "unknown func bpf_panic"),
+				"!destructive_bpf_enabled verifier log")) {
+			printf("verifier log:\n%s\n", bpf_vlog);
+		}
+	}
+	close(map_fd);
+}
+
+void test_bpf_panic(void)
+{
+	char destructive_bpf_enabled_orig[32] = {};
+
+	if (!ASSERT_OK(sysctl_get("/proc/sys/kernel/destructive_bpf_enabled",
+			 destructive_bpf_enabled_orig), "read destructive_bpf_enabled"))
+		goto cleanup;
+
+	libbpf_set_strict_mode(LIBBPF_STRICT_ALL);
+	if (test__start_subtest("bpf_panic_conditions"))
+		test_bpf_panic_conditions();
+
+cleanup:
+	if (strlen(destructive_bpf_enabled_orig) > 0)
+		sysctl_set("/proc/sys/kernel/destructive_bpf_enabled",
+				destructive_bpf_enabled_orig);
+}
-- 
2.35.3