tools: bpftool: add probes for /proc/ eBPF parameters

Add a set of probes to dump the eBPF-related parameters available from
/proc/: availability of bpf() syscall for unprivileged users,
JIT compiler status and hardening status, kallsyms exports status.

Sample output:

    # bpftool feature probe kernel
    Scanning system configuration...
    bpf() syscall for unprivileged users is enabled
    JIT compiler is disabled
    JIT compiler hardening is disabled
    JIT compiler kallsyms exports are disabled
    Global memory limit for JIT compiler for unprivileged users \
            is 264241152 bytes
    ...

    # bpftool --json --pretty feature probe kernel
    {
        "system_config": {
            "unprivileged_bpf_disabled": 0,
            "bpf_jit_enable": 0,
            "bpf_jit_harden": 0,
            "bpf_jit_kallsyms": 0,
            "bpf_jit_limit": 264241152
        },
        ...
    }

These probes are skipped if procfs is not mounted.

v4:
- Add bpf_jit_limit parameter.

v2:
- Remove C-style macros output from this patch.
Signed-off-by: Quentin Monnet <quentin.monnet@netronome.com>
Reviewed-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Reviewed-by: Stanislav Fomichev <sdf@google.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

tools/bpf/bpftool/feature.c

@@ -5,6 +5,7 @@
 #include <string.h>
 #include <unistd.h>
 #include <sys/utsname.h>
+#include <sys/vfs.h>
 
 #include <linux/filter.h>
 #include <linux/limits.h>
@@ -13,11 +14,29 @@
 
 #include "main.h"
 
+#ifndef PROC_SUPER_MAGIC
+# define PROC_SUPER_MAGIC	0x9fa0
+#endif
+
 enum probe_component {
 	COMPONENT_UNSPEC,
 	COMPONENT_KERNEL,
 };
 
+/* 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;
+}
+
 /* Printing utility functions */
 
 static void
@@ -42,6 +61,153 @@ print_start_section(const char *json_title, const char *plain_title)
 
 /* Probing functions */
 
+static int read_procfs(const char *path)
+{
+	char *endptr, *line = NULL;
+	size_t len = 0;
+	FILE *fd;
+	int 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)
+{
+	int res;
+
+	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 %d\n", res);
+		}
+	}
+}
+
+static void probe_jit_enable(void)
+{
+	int res;
+
+	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 %d\n",
+			       res);
+		}
+	}
+}
+
+static void probe_jit_harden(void)
+{
+	int res;
+
+	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 %d\n",
+			       res);
+		}
+	}
+}
+
+static void probe_jit_kallsyms(void)
+{
+	int res;
+
+	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 %d\n", res);
+		}
+	}
+}
+
+static void probe_jit_limit(void)
+{
+	int res;
+
+	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 %d bytes\n", res);
+		}
+	}
+}
+
 static bool probe_bpf_syscall(void)
 {
 	bool res;
@@ -88,6 +254,27 @@ static int do_probe(int argc, char **argv)
 	if (json_output)
 		jsonw_start_object(json_wtr);
 
+	switch (target) {
+	case COMPONENT_KERNEL:
+	case COMPONENT_UNSPEC:
+		print_start_section("system_config",
+				    "Scanning system configuration...");
+		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 */");
+		}
+		if (json_output)
+			jsonw_end_object(json_wtr);
+		else
+			printf("\n");
+		break;
+	}
+
 	print_start_section("syscall_config",
 			    "Scanning system call availability...");