Adding upstream version 5.10.209.upstream/5.10.209upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1019 insertions, 0 deletions

diff --git a/tools/bpf/bpftool/feature.c b/tools/bpf/bpftool/feature.c
new file mode 100644
index 000000000..5f0b13977
--- /dev/null
+++ b/tools/bpf/bpftool/feature.c
@@ -0,0 +1,1019 @@
+// SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+/* Copyright (c) 2019 Netronome Systems, Inc. */
+
+#include <ctype.h>
+#include <errno.h>
+#include <string.h>
+#include <unistd.h>
+#include <net/if.h>
+#ifdef USE_LIBCAP
+#include <sys/capability.h>
+#endif
+#include <sys/utsname.h>
+#include <sys/vfs.h>
+
+#include <linux/filter.h>
+#include <linux/limits.h>
+
+#include <bpf/bpf.h>
+#include <bpf/libbpf.h>
+#include <zlib.h>
+
+#include "main.h"
+
+#ifndef PROC_SUPER_MAGIC
+# define PROC_SUPER_MAGIC	0x9fa0
+#endif
+
+enum probe_component {
+	COMPONENT_UNSPEC,
+	COMPONENT_KERNEL,
+	COMPONENT_DEVICE,
+};
+
+#define BPF_HELPER_MAKE_ENTRY(name)	[BPF_FUNC_ ## name] = "bpf_" # name
+static const char * const helper_name[] = {
+	__BPF_FUNC_MAPPER(BPF_HELPER_MAKE_ENTRY)
+};
+
+#undef BPF_HELPER_MAKE_ENTRY
+
+static bool full_mode;
+#ifdef USE_LIBCAP
+static bool run_as_unprivileged;
+#endif
+
+/* Miscellaneous utility functions */
+
+static bool check_procfs(void)
+{
+	struct statfs st_fs;
+
+	if (statfs("/proc", &st_fs) < 0)
+		return false;
+	if ((unsigned long)st_fs.f_type != PROC_SUPER_MAGIC)
+		return false;
+
+	return true;
+}
+
+static void uppercase(char *str, size_t len)
+{
+	size_t i;
+
+	for (i = 0; i < len && str[i] != '\0'; i++)
+		str[i] = toupper(str[i]);
+}
+
+/* Printing utility functions */
+
+static void
+print_bool_feature(const char *feat_name, const char *plain_name,
+		   const char *define_name, bool res, const char *define_prefix)
+{
+	if (json_output)
+		jsonw_bool_field(json_wtr, feat_name, res);
+	else if (define_prefix)
+		printf("#define %s%sHAVE_%s\n", define_prefix,
+		       res ? "" : "NO_", define_name);
+	else
+		printf("%s is %savailable\n", plain_name, res ? "" : "NOT ");
+}
+
+static void print_kernel_option(const char *name, const char *value,
+				const char *define_prefix)
+{
+	char *endptr;
+	int res;
+
+	if (json_output) {
+		if (!value) {
+			jsonw_null_field(json_wtr, name);
+			return;
+		}
+		errno = 0;
+		res = strtol(value, &endptr, 0);
+		if (!errno && *endptr == '\n')
+			jsonw_int_field(json_wtr, name, res);
+		else
+			jsonw_string_field(json_wtr, name, value);
+	} else if (define_prefix) {
+		if (value)
+			printf("#define %s%s %s\n", define_prefix,
+			       name, value);
+		else
+			printf("/* %s%s is not set */\n", define_prefix, name);
+	} else {
+		if (value)
+			printf("%s is set to %s\n", name, value);
+		else
+			printf("%s is not set\n", name);
+	}
+}
+
+static void
+print_start_section(const char *json_title, const char *plain_title,
+		    const char *define_comment, const char *define_prefix)
+{
+	if (json_output) {
+		jsonw_name(json_wtr, json_title);
+		jsonw_start_object(json_wtr);
+	} else if (define_prefix) {
+		printf("%s\n", define_comment);
+	} else {
+		printf("%s\n", plain_title);
+	}
+}
+
+static void print_end_section(void)
+{
+	if (json_output)
+		jsonw_end_object(json_wtr);
+	else
+		printf("\n");
+}
+
+/* Probing functions */
+
+static long read_procfs(const char *path)
+{
+	char *endptr, *line = NULL;
+	size_t len = 0;
+	FILE *fd;
+	long res;
+
+	fd = fopen(path, "r");
+	if (!fd)
+		return -1;
+
+	res = getline(&line, &len, fd);
+	fclose(fd);
+	if (res < 0)
+		return -1;
+
+	errno = 0;
+	res = strtol(line, &endptr, 10);
+	if (errno || *line == '\0' || *endptr != '\n')
+		res = -1;
+	free(line);
+
+	return res;
+}
+
+static void probe_unprivileged_disabled(void)
+{
+	long res;
+
+	/* No support for C-style ouptut */
+
+	res = read_procfs("/proc/sys/kernel/unprivileged_bpf_disabled");
+	if (json_output) {
+		jsonw_int_field(json_wtr, "unprivileged_bpf_disabled", res);
+	} else {
+		switch (res) {
+		case 0:
+			printf("bpf() syscall for unprivileged users is enabled\n");
+			break;
+		case 1:
+			printf("bpf() syscall restricted to privileged users\n");
+			break;
+		case -1:
+			printf("Unable to retrieve required privileges for bpf() syscall\n");
+			break;
+		default:
+			printf("bpf() syscall restriction has unknown value %ld\n", res);
+		}
+	}
+}
+
+static void probe_jit_enable(void)
+{
+	long res;
+
+	/* No support for C-style ouptut */
+
+	res = read_procfs("/proc/sys/net/core/bpf_jit_enable");
+	if (json_output) {
+		jsonw_int_field(json_wtr, "bpf_jit_enable", res);
+	} else {
+		switch (res) {
+		case 0:
+			printf("JIT compiler is disabled\n");
+			break;
+		case 1:
+			printf("JIT compiler is enabled\n");
+			break;
+		case 2:
+			printf("JIT compiler is enabled with debugging traces in kernel logs\n");
+			break;
+		case -1:
+			printf("Unable to retrieve JIT-compiler status\n");
+			break;
+		default:
+			printf("JIT-compiler status has unknown value %ld\n",
+			       res);
+		}
+	}
+}
+
+static void probe_jit_harden(void)
+{
+	long res;
+
+	/* No support for C-style ouptut */
+
+	res = read_procfs("/proc/sys/net/core/bpf_jit_harden");
+	if (json_output) {
+		jsonw_int_field(json_wtr, "bpf_jit_harden", res);
+	} else {
+		switch (res) {
+		case 0:
+			printf("JIT compiler hardening is disabled\n");
+			break;
+		case 1:
+			printf("JIT compiler hardening is enabled for unprivileged users\n");
+			break;
+		case 2:
+			printf("JIT compiler hardening is enabled for all users\n");
+			break;
+		case -1:
+			printf("Unable to retrieve JIT hardening status\n");
+			break;
+		default:
+			printf("JIT hardening status has unknown value %ld\n",
+			       res);
+		}
+	}
+}
+
+static void probe_jit_kallsyms(void)
+{
+	long res;
+
+	/* No support for C-style ouptut */
+
+	res = read_procfs("/proc/sys/net/core/bpf_jit_kallsyms");
+	if (json_output) {
+		jsonw_int_field(json_wtr, "bpf_jit_kallsyms", res);
+	} else {
+		switch (res) {
+		case 0:
+			printf("JIT compiler kallsyms exports are disabled\n");
+			break;
+		case 1:
+			printf("JIT compiler kallsyms exports are enabled for root\n");
+			break;
+		case -1:
+			printf("Unable to retrieve JIT kallsyms export status\n");
+			break;
+		default:
+			printf("JIT kallsyms exports status has unknown value %ld\n", res);
+		}
+	}
+}
+
+static void probe_jit_limit(void)
+{
+	long res;
+
+	/* No support for C-style ouptut */
+
+	res = read_procfs("/proc/sys/net/core/bpf_jit_limit");
+	if (json_output) {
+		jsonw_int_field(json_wtr, "bpf_jit_limit", res);
+	} else {
+		switch (res) {
+		case -1:
+			printf("Unable to retrieve global memory limit for JIT compiler for unprivileged users\n");
+			break;
+		default:
+			printf("Global memory limit for JIT compiler for unprivileged users is %ld bytes\n", res);
+		}
+	}
+}
+
+static bool read_next_kernel_config_option(gzFile file, char *buf, size_t n,
+					   char **value)
+{
+	char *sep;
+
+	while (gzgets(file, buf, n)) {
+		if (strncmp(buf, "CONFIG_", 7))
+			continue;
+
+		sep = strchr(buf, '=');
+		if (!sep)
+			continue;
+
+		/* Trim ending '\n' */
+		buf[strlen(buf) - 1] = '\0';
+
+		/* Split on '=' and ensure that a value is present. */
+		*sep = '\0';
+		if (!sep[1])
+			continue;
+
+		*value = sep + 1;
+		return true;
+	}
+
+	return false;
+}
+
+static void probe_kernel_image_config(const char *define_prefix)
+{
+	static const struct {
+		const char * const name;
+		bool macro_dump;
+	} options[] = {
+		/* Enable BPF */
+		{ "CONFIG_BPF", },
+		/* Enable bpf() syscall */
+		{ "CONFIG_BPF_SYSCALL", },
+		/* Does selected architecture support eBPF JIT compiler */
+		{ "CONFIG_HAVE_EBPF_JIT", },
+		/* Compile eBPF JIT compiler */
+		{ "CONFIG_BPF_JIT", },
+		/* Avoid compiling eBPF interpreter (use JIT only) */
+		{ "CONFIG_BPF_JIT_ALWAYS_ON", },
+
+		/* cgroups */
+		{ "CONFIG_CGROUPS", },
+		/* BPF programs attached to cgroups */
+		{ "CONFIG_CGROUP_BPF", },
+		/* bpf_get_cgroup_classid() helper */
+		{ "CONFIG_CGROUP_NET_CLASSID", },
+		/* bpf_skb_{,ancestor_}cgroup_id() helpers */
+		{ "CONFIG_SOCK_CGROUP_DATA", },
+
+		/* Tracing: attach BPF to kprobes, tracepoints, etc. */
+		{ "CONFIG_BPF_EVENTS", },
+		/* Kprobes */
+		{ "CONFIG_KPROBE_EVENTS", },
+		/* Uprobes */
+		{ "CONFIG_UPROBE_EVENTS", },
+		/* Tracepoints */
+		{ "CONFIG_TRACING", },
+		/* Syscall tracepoints */
+		{ "CONFIG_FTRACE_SYSCALLS", },
+		/* bpf_override_return() helper support for selected arch */
+		{ "CONFIG_FUNCTION_ERROR_INJECTION", },
+		/* bpf_override_return() helper */
+		{ "CONFIG_BPF_KPROBE_OVERRIDE", },
+
+		/* Network */
+		{ "CONFIG_NET", },
+		/* AF_XDP sockets */
+		{ "CONFIG_XDP_SOCKETS", },
+		/* BPF_PROG_TYPE_LWT_* and related helpers */
+		{ "CONFIG_LWTUNNEL_BPF", },
+		/* BPF_PROG_TYPE_SCHED_ACT, TC (traffic control) actions */
+		{ "CONFIG_NET_ACT_BPF", },
+		/* BPF_PROG_TYPE_SCHED_CLS, TC filters */
+		{ "CONFIG_NET_CLS_BPF", },
+		/* TC clsact qdisc */
+		{ "CONFIG_NET_CLS_ACT", },
+		/* Ingress filtering with TC */
+		{ "CONFIG_NET_SCH_INGRESS", },
+		/* bpf_skb_get_xfrm_state() helper */
+		{ "CONFIG_XFRM", },
+		/* bpf_get_route_realm() helper */
+		{ "CONFIG_IP_ROUTE_CLASSID", },
+		/* BPF_PROG_TYPE_LWT_SEG6_LOCAL and related helpers */
+		{ "CONFIG_IPV6_SEG6_BPF", },
+		/* BPF_PROG_TYPE_LIRC_MODE2 and related helpers */
+		{ "CONFIG_BPF_LIRC_MODE2", },
+		/* BPF stream parser and BPF socket maps */
+		{ "CONFIG_BPF_STREAM_PARSER", },
+		/* xt_bpf module for passing BPF programs to netfilter  */
+		{ "CONFIG_NETFILTER_XT_MATCH_BPF", },
+		/* bpfilter back-end for iptables */
+		{ "CONFIG_BPFILTER", },
+		/* bpftilter module with "user mode helper" */
+		{ "CONFIG_BPFILTER_UMH", },
+
+		/* test_bpf module for BPF tests */
+		{ "CONFIG_TEST_BPF", },
+
+		/* Misc configs useful in BPF C programs */
+		/* jiffies <-> sec conversion for bpf_jiffies64() helper */
+		{ "CONFIG_HZ", true, }
+	};
+	char *values[ARRAY_SIZE(options)] = { };
+	struct utsname utsn;
+	char path[PATH_MAX];
+	gzFile file = NULL;
+	char buf[4096];
+	char *value;
+	size_t i;
+
+	if (!uname(&utsn)) {
+		snprintf(path, sizeof(path), "/boot/config-%s", utsn.release);
+
+		/* gzopen also accepts uncompressed files. */
+		file = gzopen(path, "r");
+	}
+
+	if (!file) {
+		/* Some distributions build with CONFIG_IKCONFIG=y and put the
+		 * config file at /proc/config.gz.
+		 */
+		file = gzopen("/proc/config.gz", "r");
+	}
+	if (!file) {
+		p_info("skipping kernel config, can't open file: %s",
+		       strerror(errno));
+		goto end_parse;
+	}
+	/* Sanity checks */
+	if (!gzgets(file, buf, sizeof(buf)) ||
+	    !gzgets(file, buf, sizeof(buf))) {
+		p_info("skipping kernel config, can't read from file: %s",
+		       strerror(errno));
+		goto end_parse;
+	}
+	if (strcmp(buf, "# Automatically generated file; DO NOT EDIT.\n")) {
+		p_info("skipping kernel config, can't find correct file");
+		goto end_parse;
+	}
+
+	while (read_next_kernel_config_option(file, buf, sizeof(buf), &value)) {
+		for (i = 0; i < ARRAY_SIZE(options); i++) {
+			if ((define_prefix && !options[i].macro_dump) ||
+			    values[i] || strcmp(buf, options[i].name))
+				continue;
+
+			values[i] = strdup(value);
+		}
+	}
+
+end_parse:
+	if (file)
+		gzclose(file);
+
+	for (i = 0; i < ARRAY_SIZE(options); i++) {
+		if (define_prefix && !options[i].macro_dump)
+			continue;
+		print_kernel_option(options[i].name, values[i], define_prefix);
+		free(values[i]);
+	}
+}
+
+static bool probe_bpf_syscall(const char *define_prefix)
+{
+	bool res;
+
+	bpf_load_program(BPF_PROG_TYPE_UNSPEC, NULL, 0, NULL, 0, NULL, 0);
+	res = (errno != ENOSYS);
+
+	print_bool_feature("have_bpf_syscall",
+			   "bpf() syscall",
+			   "BPF_SYSCALL",
+			   res, define_prefix);
+
+	return res;
+}
+
+static void
+probe_prog_type(enum bpf_prog_type prog_type, bool *supported_types,
+		const char *define_prefix, __u32 ifindex)
+{
+	char feat_name[128], plain_desc[128], define_name[128];
+	const char *plain_comment = "eBPF program_type ";
+	size_t maxlen;
+	bool res;
+
+	if (ifindex)
+		/* Only test offload-able program types */
+		switch (prog_type) {
+		case BPF_PROG_TYPE_SCHED_CLS:
+		case BPF_PROG_TYPE_XDP:
+			break;
+		default:
+			return;
+		}
+
+	res = bpf_probe_prog_type(prog_type, ifindex);
+#ifdef USE_LIBCAP
+	/* Probe may succeed even if program load fails, for unprivileged users
+	 * check that we did not fail because of insufficient permissions
+	 */
+	if (run_as_unprivileged && errno == EPERM)
+		res = false;
+#endif
+
+	supported_types[prog_type] |= res;
+
+	if (!prog_type_name[prog_type]) {
+		p_info("program type name not found (type %d)", prog_type);
+		return;
+	}
+	maxlen = sizeof(plain_desc) - strlen(plain_comment) - 1;
+	if (strlen(prog_type_name[prog_type]) > maxlen) {
+		p_info("program type name too long");
+		return;
+	}
+
+	sprintf(feat_name, "have_%s_prog_type", prog_type_name[prog_type]);
+	sprintf(define_name, "%s_prog_type", prog_type_name[prog_type]);
+	uppercase(define_name, sizeof(define_name));
+	sprintf(plain_desc, "%s%s", plain_comment, prog_type_name[prog_type]);
+	print_bool_feature(feat_name, plain_desc, define_name, res,
+			   define_prefix);
+}
+
+static void
+probe_map_type(enum bpf_map_type map_type, const char *define_prefix,
+	       __u32 ifindex)
+{
+	char feat_name[128], plain_desc[128], define_name[128];
+	const char *plain_comment = "eBPF map_type ";
+	size_t maxlen;
+	bool res;
+
+	res = bpf_probe_map_type(map_type, ifindex);
+
+	/* Probe result depends on the success of map creation, no additional
+	 * check required for unprivileged users
+	 */
+
+	if (!map_type_name[map_type]) {
+		p_info("map type name not found (type %d)", map_type);
+		return;
+	}
+	maxlen = sizeof(plain_desc) - strlen(plain_comment) - 1;
+	if (strlen(map_type_name[map_type]) > maxlen) {
+		p_info("map type name too long");
+		return;
+	}
+
+	sprintf(feat_name, "have_%s_map_type", map_type_name[map_type]);
+	sprintf(define_name, "%s_map_type", map_type_name[map_type]);
+	uppercase(define_name, sizeof(define_name));
+	sprintf(plain_desc, "%s%s", plain_comment, map_type_name[map_type]);
+	print_bool_feature(feat_name, plain_desc, define_name, res,
+			   define_prefix);
+}
+
+static void
+probe_helper_for_progtype(enum bpf_prog_type prog_type, bool supported_type,
+			  const char *define_prefix, unsigned int id,
+			  const char *ptype_name, __u32 ifindex)
+{
+	bool res = false;
+
+	if (supported_type) {
+		res = bpf_probe_helper(id, prog_type, ifindex);
+#ifdef USE_LIBCAP
+		/* Probe may succeed even if program load fails, for
+		 * unprivileged users check that we did not fail because of
+		 * insufficient permissions
+		 */
+		if (run_as_unprivileged && errno == EPERM)
+			res = false;
+#endif
+	}
+
+	if (json_output) {
+		if (res)
+			jsonw_string(json_wtr, helper_name[id]);
+	} else if (define_prefix) {
+		printf("#define %sBPF__PROG_TYPE_%s__HELPER_%s %s\n",
+		       define_prefix, ptype_name, helper_name[id],
+		       res ? "1" : "0");
+	} else {
+		if (res)
+			printf("\n\t- %s", helper_name[id]);
+	}
+}
+
+static void
+probe_helpers_for_progtype(enum bpf_prog_type prog_type, bool supported_type,
+			   const char *define_prefix, __u32 ifindex)
+{
+	const char *ptype_name = prog_type_name[prog_type];
+	char feat_name[128];
+	unsigned int id;
+
+	if (ifindex)
+		/* Only test helpers for offload-able program types */
+		switch (prog_type) {
+		case BPF_PROG_TYPE_SCHED_CLS:
+		case BPF_PROG_TYPE_XDP:
+			break;
+		default:
+			return;
+		}
+
+	if (json_output) {
+		sprintf(feat_name, "%s_available_helpers", ptype_name);
+		jsonw_name(json_wtr, feat_name);
+		jsonw_start_array(json_wtr);
+	} else if (!define_prefix) {
+		printf("eBPF helpers supported for program type %s:",
+		       ptype_name);
+	}
+
+	for (id = 1; id < ARRAY_SIZE(helper_name); id++) {
+		/* Skip helper functions which emit dmesg messages when not in
+		 * the full mode.
+		 */
+		switch (id) {
+		case BPF_FUNC_trace_printk:
+		case BPF_FUNC_probe_write_user:
+			if (!full_mode)
+				continue;
+			/* fallthrough */
+		default:
+			probe_helper_for_progtype(prog_type, supported_type,
+						  define_prefix, id, ptype_name,
+						  ifindex);
+		}
+	}
+
+	if (json_output)
+		jsonw_end_array(json_wtr);
+	else if (!define_prefix)
+		printf("\n");
+}
+
+static void
+probe_large_insn_limit(const char *define_prefix, __u32 ifindex)
+{
+	bool res;
+
+	res = bpf_probe_large_insn_limit(ifindex);
+	print_bool_feature("have_large_insn_limit",
+			   "Large program size limit",
+			   "LARGE_INSN_LIMIT",
+			   res, define_prefix);
+}
+
+static void
+section_system_config(enum probe_component target, const char *define_prefix)
+{
+	switch (target) {
+	case COMPONENT_KERNEL:
+	case COMPONENT_UNSPEC:
+		print_start_section("system_config",
+				    "Scanning system configuration...",
+				    "/*** Misc kernel config items ***/",
+				    define_prefix);
+		if (!define_prefix) {
+			if (check_procfs()) {
+				probe_unprivileged_disabled();
+				probe_jit_enable();
+				probe_jit_harden();
+				probe_jit_kallsyms();
+				probe_jit_limit();
+			} else {
+				p_info("/* procfs not mounted, skipping related probes */");
+			}
+		}
+		probe_kernel_image_config(define_prefix);
+		print_end_section();
+		break;
+	default:
+		break;
+	}
+}
+
+static bool section_syscall_config(const char *define_prefix)
+{
+	bool res;
+
+	print_start_section("syscall_config",
+			    "Scanning system call availability...",
+			    "/*** System call availability ***/",
+			    define_prefix);
+	res = probe_bpf_syscall(define_prefix);
+	print_end_section();
+
+	return res;
+}
+
+static void
+section_program_types(bool *supported_types, const char *define_prefix,
+		      __u32 ifindex)
+{
+	unsigned int i;
+
+	print_start_section("program_types",
+			    "Scanning eBPF program types...",
+			    "/*** eBPF program types ***/",
+			    define_prefix);
+
+	for (i = BPF_PROG_TYPE_UNSPEC + 1; i < prog_type_name_size; i++)
+		probe_prog_type(i, supported_types, define_prefix, ifindex);
+
+	print_end_section();
+}
+
+static void section_map_types(const char *define_prefix, __u32 ifindex)
+{
+	unsigned int i;
+
+	print_start_section("map_types",
+			    "Scanning eBPF map types...",
+			    "/*** eBPF map types ***/",
+			    define_prefix);
+
+	for (i = BPF_MAP_TYPE_UNSPEC + 1; i < map_type_name_size; i++)
+		probe_map_type(i, define_prefix, ifindex);
+
+	print_end_section();
+}
+
+static void
+section_helpers(bool *supported_types, const char *define_prefix, __u32 ifindex)
+{
+	unsigned int i;
+
+	print_start_section("helpers",
+			    "Scanning eBPF helper functions...",
+			    "/*** eBPF helper functions ***/",
+			    define_prefix);
+
+	if (define_prefix)
+		printf("/*\n"
+		       " * Use %sHAVE_PROG_TYPE_HELPER(prog_type_name, helper_name)\n"
+		       " * to determine if <helper_name> is available for <prog_type_name>,\n"
+		       " * e.g.\n"
+		       " *	#if %sHAVE_PROG_TYPE_HELPER(xdp, bpf_redirect)\n"
+		       " *		// do stuff with this helper\n"
+		       " *	#elif\n"
+		       " *		// use a workaround\n"
+		       " *	#endif\n"
+		       " */\n"
+		       "#define %sHAVE_PROG_TYPE_HELPER(prog_type, helper)	\\\n"
+		       "	%sBPF__PROG_TYPE_ ## prog_type ## __HELPER_ ## helper\n",
+		       define_prefix, define_prefix, define_prefix,
+		       define_prefix);
+	for (i = BPF_PROG_TYPE_UNSPEC + 1; i < prog_type_name_size; i++)
+		probe_helpers_for_progtype(i, supported_types[i], define_prefix,
+					   ifindex);
+
+	print_end_section();
+}
+
+static void section_misc(const char *define_prefix, __u32 ifindex)
+{
+	print_start_section("misc",
+			    "Scanning miscellaneous eBPF features...",
+			    "/*** eBPF misc features ***/",
+			    define_prefix);
+	probe_large_insn_limit(define_prefix, ifindex);
+	print_end_section();
+}
+
+#ifdef USE_LIBCAP
+#define capability(c) { c, false, #c }
+#define capability_msg(a, i) a[i].set ? "" : a[i].name, a[i].set ? "" : ", "
+#endif
+
+static int handle_perms(void)
+{
+#ifdef USE_LIBCAP
+	struct {
+		cap_value_t cap;
+		bool set;
+		char name[14];	/* strlen("CAP_SYS_ADMIN") */
+	} bpf_caps[] = {
+		capability(CAP_SYS_ADMIN),
+#ifdef CAP_BPF
+		capability(CAP_BPF),
+		capability(CAP_NET_ADMIN),
+		capability(CAP_PERFMON),
+#endif
+	};
+	cap_value_t cap_list[ARRAY_SIZE(bpf_caps)];
+	unsigned int i, nb_bpf_caps = 0;
+	bool cap_sys_admin_only = true;
+	cap_flag_value_t val;
+	int res = -1;
+	cap_t caps;
+
+	caps = cap_get_proc();
+	if (!caps) {
+		p_err("failed to get capabilities for process: %s",
+		      strerror(errno));
+		return -1;
+	}
+
+#ifdef CAP_BPF
+	if (CAP_IS_SUPPORTED(CAP_BPF))
+		cap_sys_admin_only = false;
+#endif
+
+	for (i = 0; i < ARRAY_SIZE(bpf_caps); i++) {
+		const char *cap_name = bpf_caps[i].name;
+		cap_value_t cap = bpf_caps[i].cap;
+
+		if (cap_get_flag(caps, cap, CAP_EFFECTIVE, &val)) {
+			p_err("bug: failed to retrieve %s status: %s", cap_name,
+			      strerror(errno));
+			goto exit_free;
+		}
+
+		if (val == CAP_SET) {
+			bpf_caps[i].set = true;
+			cap_list[nb_bpf_caps++] = cap;
+		}
+
+		if (cap_sys_admin_only)
+			/* System does not know about CAP_BPF, meaning that
+			 * CAP_SYS_ADMIN is the only capability required. We
+			 * just checked it, break.
+			 */
+			break;
+	}
+
+	if ((run_as_unprivileged && !nb_bpf_caps) ||
+	    (!run_as_unprivileged && nb_bpf_caps == ARRAY_SIZE(bpf_caps)) ||
+	    (!run_as_unprivileged && cap_sys_admin_only && nb_bpf_caps)) {
+		/* We are all good, exit now */
+		res = 0;
+		goto exit_free;
+	}
+
+	if (!run_as_unprivileged) {
+		if (cap_sys_admin_only)
+			p_err("missing %s, required for full feature probing; run as root or use 'unprivileged'",
+			      bpf_caps[0].name);
+		else
+			p_err("missing %s%s%s%s%s%s%s%srequired for full feature probing; run as root or use 'unprivileged'",
+			      capability_msg(bpf_caps, 0),
+#ifdef CAP_BPF
+			      capability_msg(bpf_caps, 1),
+			      capability_msg(bpf_caps, 2),
+			      capability_msg(bpf_caps, 3)
+#else
+				"", "", "", "", "", ""
+#endif /* CAP_BPF */
+				);
+		goto exit_free;
+	}
+
+	/* if (run_as_unprivileged && nb_bpf_caps > 0), drop capabilities. */
+	if (cap_set_flag(caps, CAP_EFFECTIVE, nb_bpf_caps, cap_list,
+			 CAP_CLEAR)) {
+		p_err("bug: failed to clear capabilities: %s", strerror(errno));
+		goto exit_free;
+	}
+
+	if (cap_set_proc(caps)) {
+		p_err("failed to drop capabilities: %s", strerror(errno));
+		goto exit_free;
+	}
+
+	res = 0;
+
+exit_free:
+	if (cap_free(caps) && !res) {
+		p_err("failed to clear storage object for capabilities: %s",
+		      strerror(errno));
+		res = -1;
+	}
+
+	return res;
+#else
+	/* Detection assumes user has specific privileges.
+	 * We do not use libpcap so let's approximate, and restrict usage to
+	 * root user only.
+	 */
+	if (geteuid()) {
+		p_err("full feature probing requires root privileges");
+		return -1;
+	}
+
+	return 0;
+#endif /* USE_LIBCAP */
+}
+
+static int do_probe(int argc, char **argv)
+{
+	enum probe_component target = COMPONENT_UNSPEC;
+	const char *define_prefix = NULL;
+	bool supported_types[128] = {};
+	__u32 ifindex = 0;
+	char *ifname;
+
+	set_max_rlimit();
+
+	while (argc) {
+		if (is_prefix(*argv, "kernel")) {
+			if (target != COMPONENT_UNSPEC) {
+				p_err("component to probe already specified");
+				return -1;
+			}
+			target = COMPONENT_KERNEL;
+			NEXT_ARG();
+		} else if (is_prefix(*argv, "dev")) {
+			NEXT_ARG();
+
+			if (target != COMPONENT_UNSPEC || ifindex) {
+				p_err("component to probe already specified");
+				return -1;
+			}
+			if (!REQ_ARGS(1))
+				return -1;
+
+			target = COMPONENT_DEVICE;
+			ifname = GET_ARG();
+			ifindex = if_nametoindex(ifname);
+			if (!ifindex) {
+				p_err("unrecognized netdevice '%s': %s", ifname,
+				      strerror(errno));
+				return -1;
+			}
+		} else if (is_prefix(*argv, "full")) {
+			full_mode = true;
+			NEXT_ARG();
+		} else if (is_prefix(*argv, "macros") && !define_prefix) {
+			define_prefix = "";
+			NEXT_ARG();
+		} else if (is_prefix(*argv, "prefix")) {
+			if (!define_prefix) {
+				p_err("'prefix' argument can only be use after 'macros'");
+				return -1;
+			}
+			if (strcmp(define_prefix, "")) {
+				p_err("'prefix' already defined");
+				return -1;
+			}
+			NEXT_ARG();
+
+			if (!REQ_ARGS(1))
+				return -1;
+			define_prefix = GET_ARG();
+		} else if (is_prefix(*argv, "unprivileged")) {
+#ifdef USE_LIBCAP
+			run_as_unprivileged = true;
+			NEXT_ARG();
+#else
+			p_err("unprivileged run not supported, recompile bpftool with libcap");
+			return -1;
+#endif
+		} else {
+			p_err("expected no more arguments, 'kernel', 'dev', 'macros' or 'prefix', got: '%s'?",
+			      *argv);
+			return -1;
+		}
+	}
+
+	/* Full feature detection requires specific privileges.
+	 * Let's approximate, and warn if user is not root.
+	 */
+	if (handle_perms())
+		return -1;
+
+	if (json_output) {
+		define_prefix = NULL;
+		jsonw_start_object(json_wtr);
+	}
+
+	section_system_config(target, define_prefix);
+	if (!section_syscall_config(define_prefix))
+		/* bpf() syscall unavailable, don't probe other BPF features */
+		goto exit_close_json;
+	section_program_types(supported_types, define_prefix, ifindex);
+	section_map_types(define_prefix, ifindex);
+	section_helpers(supported_types, define_prefix, ifindex);
+	section_misc(define_prefix, ifindex);
+
+exit_close_json:
+	if (json_output)
+		/* End root object */
+		jsonw_end_object(json_wtr);
+
+	return 0;
+}
+
+static int do_help(int argc, char **argv)
+{
+	if (json_output) {
+		jsonw_null(json_wtr);
+		return 0;
+	}
+
+	fprintf(stderr,
+		"Usage: %1$s %2$s probe [COMPONENT] [full] [unprivileged] [macros [prefix PREFIX]]\n"
+		"       %1$s %2$s help\n"
+		"\n"
+		"       COMPONENT := { kernel | dev NAME }\n"
+		"",
+		bin_name, argv[-2]);
+
+	return 0;
+}
+
+static const struct cmd cmds[] = {
+	{ "probe",	do_probe },
+	{ "help",	do_help },
+	{ 0 }
+};
+
+int do_feature(int argc, char **argv)
+{
+	return cmd_select(cmds, argc, argv, do_help);
+}