From: Eduard Zingerman Date: Tue, 17 Jun 2025 00:57:10 +0000 (-0700) Subject: selftests/bpf: More precise cpu_mitigations state detection X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=fc2915bb8bfcfdc6e5ea2cfc8d13fbaefe77c2c8;p=thirdparty%2Fkernel%2Flinux.git selftests/bpf: More precise cpu_mitigations state detection test_progs and test_verifier binaries execute unpriv tests under the following conditions: - unpriv BPF is enabled; - CPU mitigations are enabled (see [1] for details). The detection of the "mitigations enabled" state is performed by unpriv_helpers.c:get_mitigations_off() via inspecting kernel boot command line, looking for a parameter "mitigations=off". Such detection scheme won't work for certain configurations, e.g. when CONFIG_CPU_MITIGATIONS is disabled and boot parameter is not supplied. Miss-detection leads to test_progs executing tests meant to be run only with mitigations enabled, e.g. verifier_and.c:known_subreg_with_unknown_reg(), and reporting false failures. Internally, verifier sets bpf_verifier_env->bypass_spec_{v1,v4} basing on the value returned by kernel/cpu.c:cpu_mitigations_off(). This function is backed by a variable kernel/cpu.c:cpu_mitigations. This state is not fully introspect-able via sysfs. The closest proxy is /sys/devices/system/cpu/vulnerabilities/spectre_v1, but it reports "vulnerable" state only if mitigations are disabled *and* current cpu is vulnerable, while verifier does not check cpu state. There are only two ways the kernel/cpu.c:cpu_mitigations can be set: - via boot parameter; - via CONFIG_CPU_MITIGATIONS option. This commit updates unpriv_helpers.c:get_mitigations_off() to scan /boot/config-$(uname -r) and /proc/config.gz for CONFIG_CPU_MITIGATIONS value in addition to boot command line check. Tested using the following configurations: - mitigations enabled (unpriv tests are enabled) - mitigations disabled via boot cmdline (unpriv tests skipped) - mitigations disabled via CONFIG_CPU_MITIGATIONS (unpriv tests skipped) [1] https://lore.kernel.org/bpf/20231025031144.5508-1-laoar.shao@gmail.com/ Reported-by: Mykyta Yatsenko Signed-off-by: Eduard Zingerman Signed-off-by: Andrii Nakryiko Link: https://lore.kernel.org/bpf/20250617005710.1066165-2-eddyz87@gmail.com --- diff --git a/tools/testing/selftests/bpf/unpriv_helpers.c b/tools/testing/selftests/bpf/unpriv_helpers.c index 220f6a9638134..3aa9ee80a55e4 100644 --- a/tools/testing/selftests/bpf/unpriv_helpers.c +++ b/tools/testing/selftests/bpf/unpriv_helpers.c @@ -1,15 +1,75 @@ // SPDX-License-Identifier: GPL-2.0-only +#include #include #include #include #include +#include #include #include +#include #include "unpriv_helpers.h" -static bool get_mitigations_off(void) +static gzFile open_config(void) +{ + struct utsname uts; + char buf[PATH_MAX]; + gzFile config; + + if (uname(&uts)) { + perror("uname"); + goto config_gz; + } + + snprintf(buf, sizeof(buf), "/boot/config-%s", uts.release); + config = gzopen(buf, "rb"); + if (config) + return config; + fprintf(stderr, "gzopen %s: %s\n", buf, strerror(errno)); + +config_gz: + config = gzopen("/proc/config.gz", "rb"); + if (!config) + perror("gzopen /proc/config.gz"); + return config; +} + +static int config_contains(const char *pat) +{ + const char *msg; + char buf[1024]; + gzFile config; + int n, err; + + config = open_config(); + if (!config) + return -1; + + for (;;) { + if (!gzgets(config, buf, sizeof(buf))) { + msg = gzerror(config, &err); + if (err == Z_ERRNO) + perror("gzgets /proc/config.gz"); + else if (err != Z_OK) + fprintf(stderr, "gzgets /proc/config.gz: %s", msg); + gzclose(config); + return -1; + } + n = strlen(buf); + if (buf[n - 1] == '\n') + buf[n - 1] = 0; + if (strcmp(buf, pat) == 0) { + gzclose(config); + return 1; + } + } + gzclose(config); + return 0; +} + +static bool cmdline_contains(const char *pat) { char cmdline[4096], *c; int fd, ret = false; @@ -27,7 +87,7 @@ static bool get_mitigations_off(void) cmdline[sizeof(cmdline) - 1] = '\0'; for (c = strtok(cmdline, " \n"); c; c = strtok(NULL, " \n")) { - if (strncmp(c, "mitigations=off", strlen(c))) + if (strncmp(c, pat, strlen(c))) continue; ret = true; break; @@ -37,8 +97,21 @@ out: return ret; } +static int get_mitigations_off(void) +{ + int enabled_in_config; + + if (cmdline_contains("mitigations=off")) + return 1; + enabled_in_config = config_contains("CONFIG_CPU_MITIGATIONS=y"); + if (enabled_in_config < 0) + return -1; + return !enabled_in_config; +} + bool get_unpriv_disabled(void) { + int mitigations_off; bool disabled; char buf[2]; FILE *fd; @@ -52,5 +125,19 @@ bool get_unpriv_disabled(void) disabled = true; } - return disabled ? true : get_mitigations_off(); + if (disabled) + return true; + + /* + * Some unpriv tests rely on spectre mitigations being on. + * If mitigations are off or status can't be determined + * assume that unpriv tests are disabled. + */ + mitigations_off = get_mitigations_off(); + if (mitigations_off < 0) { + fprintf(stderr, + "Can't determine if mitigations are enabled, disabling unpriv tests."); + return true; + } + return mitigations_off; }