On Thu, Jan 25, 2024 at 08:22:13AM +0100, Anthony Harivel wrote: > Introduce a privileged helper to access RAPL MSR. > > The privileged helper tool, qemu-vmsr-helper, is designed to provide > virtual machines with the ability to read specific RAPL (Running Average > Power Limit) MSRs without requiring CAP_SYS_RAWIO privileges or relying > on external, out-of-tree patches. > > The helper tool leverages Unix permissions and SO_PEERCRED socket > options to enforce access control, ensuring that only processes > explicitly requesting read access via readmsr() from a valid Thread ID > can access these MSRs. > > The list of RAPL MSRs that are allowed to be read by the helper tool is > defined in rapl-msr-index.h. This list corresponds to the RAPL MSRs that > will be supported in the next commit titled "Add support for RAPL MSRs > in KVM/QEMU." > > The tool is intentionally designed to run on the Linux x86 platform. > This initial implementation is tailored for Intel CPUs but can be > extended to support AMD CPUs in the future. > > Signed-off-by: Anthony Harivel <ahari...@redhat.com> > --- > contrib/systemd/qemu-vmsr-helper.service | 15 + > contrib/systemd/qemu-vmsr-helper.socket | 9 + > docs/tools/index.rst | 1 + > docs/tools/qemu-vmsr-helper.rst | 89 ++++ > meson.build | 5 + > tools/i386/qemu-vmsr-helper.c | 507 +++++++++++++++++++++++ > tools/i386/rapl-msr-index.h | 28 ++ > 7 files changed, 654 insertions(+) > create mode 100644 contrib/systemd/qemu-vmsr-helper.service > create mode 100644 contrib/systemd/qemu-vmsr-helper.socket > create mode 100644 docs/tools/qemu-vmsr-helper.rst > create mode 100644 tools/i386/qemu-vmsr-helper.c > create mode 100644 tools/i386/rapl-msr-index.h > > diff --git a/contrib/systemd/qemu-vmsr-helper.service > b/contrib/systemd/qemu-vmsr-helper.service > new file mode 100644 > index 000000000000..8fd397bf79a9 > --- /dev/null > +++ b/contrib/systemd/qemu-vmsr-helper.service > @@ -0,0 +1,15 @@ > +[Unit] > +Description=Virtual RAPL MSR Daemon for QEMU > + > +[Service] > +WorkingDirectory=/tmp > +Type=simple > +ExecStart=/usr/bin/qemu-vmsr-helper > +PrivateTmp=yes > +ProtectSystem=strict > +ReadWritePaths=/var/run > +RestrictAddressFamilies=AF_UNIX > +Restart=always > +RestartSec=0 > + > +[Install] > diff --git a/contrib/systemd/qemu-vmsr-helper.socket > b/contrib/systemd/qemu-vmsr-helper.socket > new file mode 100644 > index 000000000000..183e8304d6e2 > --- /dev/null > +++ b/contrib/systemd/qemu-vmsr-helper.socket > @@ -0,0 +1,9 @@ > +[Unit] > +Description=Virtual RAPL MSR helper for QEMU > + > +[Socket] > +ListenStream=/run/qemu-vmsr-helper.sock > +SocketMode=0600
This mode means that only root can connect to it, which seems to defeat the purpose of allowing QEMU to run as non-root surely ? > diff --git a/meson.build b/meson.build > index d0329966f1b4..93fc233b0891 100644 > --- a/meson.build > +++ b/meson.build > @@ -4015,6 +4015,11 @@ if have_tools > dependencies: [authz, crypto, io, qom, qemuutil, > libcap_ng, mpathpersist], > install: true) > + > + executable('qemu-vmsr-helper', files('tools/i386/qemu-vmsr-helper.c'), I'd suggest 'tools/x86/' since this works fine on 64-bit too > + dependencies: [authz, crypto, io, qom, qemuutil, > + libcap_ng, mpathpersist], > + install: true) Shouldn't this executable() call be conditional though, so this is only built for x86 host targets. > endif > > if have_ivshmem > diff --git a/tools/i386/qemu-vmsr-helper.c b/tools/i386/qemu-vmsr-helper.c > new file mode 100644 > index 000000000000..cf7d09bfcab3 > --- /dev/null > +++ b/tools/i386/qemu-vmsr-helper.c > + > +#define MAX_PATH_LEN 256 Drop this constant as it is redundant > +#define MSR_PATH_TEMPLATE "/dev/cpu/%u/msr" > + > +static char *socket_path; > +static char *pidfile; > +static enum { RUNNING, TERMINATE, TERMINATING } state; > +static QIOChannelSocket *server_ioc; > +static int server_watch; > +static int num_active_sockets = 1; > + > +#ifdef CONFIG_LIBCAP_NG > +static int uid = -1; > +static int gid = -1; > +#endif > + > +static void compute_default_paths(void) > +{ > + socket_path = g_build_filename("/run", "qemu-vmsr-helper.sock", NULL); > + pidfile = g_build_filename("/run", "qemu-vmsr-helper.pid", NULL); > +} We shouldn't be hardcoding /run, we need to honour --prefix and --localstatedir args given to configure. /var/run is a symlink to /run so the end result ends up the same AFAIK > + > +/* > + * Check if the TID that request the MSR read > + * belongs to the peer. It be should a TID of a vCPU. > + */ > +static bool is_tid_present(pid_t pid, pid_t tid) > +{ > + g_autofree char *pidStr; > + g_autofree char *tidStr; > + > + pidStr = g_strdup_printf("%d", pid); > + tidStr = g_strdup_printf("%d", tid); > + > + char *tidPath; This needs to be g_autofree too, and as a rule any variable declared with 'g_autofree' should always be initialized at the same time as declaration, so put the g_strdup_printf calls on the same line. > + > + tidPath = g_strdup_printf("/proc/%s/task/%s", pidStr, tidStr); > + > + /* Check if the TID directory exists within the PID directory */ > + if (access(tidPath, F_OK) == 0) { > + return true; > + } > + error_report("Failed to open /proc at %s", tidPath); > + return false; > +} > + > +/* > + * Only the RAPL MSR in target/i386/cpu.h are allowed > + */ > +static bool is_msr_allowed(uint32_t reg) > +{ > + switch (reg) { > + case MSR_RAPL_POWER_UNIT: > + case MSR_PKG_POWER_LIMIT: > + case MSR_PKG_ENERGY_STATUS: > + case MSR_PKG_POWER_INFO: > + return true; > + default: > + return false; > + } > +} > + > +static uint64_t vmsr_read_msr(uint32_t msr_register, unsigned int cpu_id) > +{ > + int fd; > + uint64_t result = 0; > + > + g_autofree char *path; > + path = g_new0(char, MAX_PATH_LEN); This is a memory leak as it is overwritten on the next line. > + path = g_strdup_printf(MSR_PATH_TEMPLATE, cpu_id); Since this constant is only used in one place, I'd prefer to see it inline here, so an observer can see what format specifiers are relied upon > + > + /* > + * Check if the specified CPU is included in the thread's affinity > + */ > + cpu_set_t cpu_set; > + CPU_ZERO(&cpu_set); > + sched_getaffinity(0, sizeof(cpu_set_t), &cpu_set); Using cpu_set_t will break on machines with >= 1024 CPUs. There are a numbr of painpoints with calling sched_getaffinity so rather than try to explain them, let me point you to the man page for sched_getaffinity underthe headeing: "Handling systems with large CPU affinity masks" > + > + if (!CPU_ISSET(cpu_id, &cpu_set)) { > + fprintf(stderr, "CPU %u is not in the thread's affinity.\n", cpu_id); Use error_report() for consistency > + return result; > + } > + > + fd = open(path, O_RDONLY); > + if (fd < 0) { > + error_report("Failed to open MSR file at %s", path); > + return result; > + } > + > + if (pread(fd, &result, sizeof(result), msr_register) != sizeof(result)) { Leaks 'fd' > + error_report("Failed to read MSR"); > + result = 0; > + } > + > + close(fd); > + return result; > +} > +static void coroutine_fn vh_co_entry(void *opaque) > +{ > + VMSRHelperClient *client = opaque; > + uint64_t vmsr; > + uint32_t request[3]; > + unsigned int peer_pid; > + int r; > + Error *local_err = NULL; > + > + qio_channel_set_blocking(QIO_CHANNEL(client->ioc), > + false, NULL); > + > + qio_channel_set_follow_coroutine_ctx(QIO_CHANNEL(client->ioc), true); > + > + /* > + * Check peer credentials > + */ > + qio_channel_get_peerpid(QIO_CHANNEL(client->ioc), &peer_pid, &local_err); > + > + if (peer_pid == 0) { > + if (local_err != NULL) { > + error_report_err(local_err); > + } > + error_report("Failed to get peer credentials"); Using peer_pid == 0 as a substitute for checking if 'local_err' is set is bogus. Check for 'local_err != NULL'. > + goto out; > + } > + > + /* > + * Read the requested MSR > + * Only RAPL MSR in rapl-msr-index.h is allowed > + */ > + r = qio_channel_read_all(QIO_CHANNEL(client->ioc), > + (char *) &request, sizeof(request), &local_err); > + if ((local_err != NULL) || r < 0) { Checking both conditions is redundant, pick one > + error_report("Read request fail"); > + error_report_err(local_err); > + goto out; > + } > + if (!is_msr_allowed(request[0])) { > + error_report("Requested unallowed msr: %d", request[0]); > + goto out; > + } > + > + vmsr = vmsr_read_msr(request[0], request[1]); > + > + if (!is_tid_present(peer_pid, request[2])) { > + error_report("Requested TID not in peer PID: %d %d", > + peer_pid, request[2]); Indent is a little off. You never answered my question from the previous posting of this This check is merely validating the the thread ID in the message is a child of the process ID connected to the socket. Any process on the entire host can satisfy this requirement. I don't see what is limiting this to only QEMU as claimed by the commit message, unless you're expecting the UNIX socket permissions to be such that only processes under the qemu:qemu user:group pair can access to the socket ? That would be a libvirt based permissions assumption though. > + vmsr = 0; > + } > + > + r = qio_channel_write_all(QIO_CHANNEL(client->ioc), > + (char *) &vmsr, sizeof(vmsr), &local_err); Indent got a little off here too. > + if ((local_err != NULL) || r < 0) { Again redundant checks > + error_report("Write request fail"); > + error_report_err(local_err); > + goto out; > + } > + > +out: > + object_unref(OBJECT(client->ioc)); > + g_free(client); > +} > + > +static gboolean accept_client(QIOChannel *ioc, > + GIOCondition cond, > + gpointer opaque) > +{ > + QIOChannelSocket *cioc; > + VMSRHelperClient *vmsrh; > + > + cioc = qio_channel_socket_accept(QIO_CHANNEL_SOCKET(ioc), > + NULL); > + if (!cioc) { > + return TRUE; > + } > + > + vmsrh = g_new(VMSRHelperClient, 1); > + vmsrh->ioc = cioc; > + vmsrh->co = qemu_coroutine_create(vh_co_entry, vmsrh); > + qemu_coroutine_enter(vmsrh->co); > + > + return TRUE; > +} > + > +static void termsig_handler(int signum) > +{ > + qatomic_cmpxchg(&state, RUNNING, TERMINATE); > + qemu_notify_event(); > +} > + > +static void close_server_socket(void) > +{ > + assert(server_ioc); > + > + g_source_remove(server_watch); > + server_watch = -1; > + object_unref(OBJECT(server_ioc)); > + num_active_sockets--; > +} > + > +#ifdef CONFIG_LIBCAP_NG > +static int drop_privileges(void) > +{ > + /* clear all capabilities */ > + capng_clear(CAPNG_SELECT_BOTH); > + > + if (capng_update(CAPNG_ADD, CAPNG_EFFECTIVE | CAPNG_PERMITTED, > + CAP_SYS_RAWIO) < 0) { > + return -1; > + } > + > + /* > + * Change user/group id, retaining the capabilities. > + * Because file descriptors are passed via SCM_RIGHTS, > + * we don't need supplementary groups (and in fact the helper > + * can run as "nobody"). > + */ > + if (capng_change_id(uid != -1 ? uid : getuid(), > + gid != -1 ? gid : getgid(), > + CAPNG_DROP_SUPP_GRP | CAPNG_CLEAR_BOUNDING)) { > + return -1; > + } Does this actually work ? IIUC, the file that requires privileges is /dev/cpu/%u/msr, and we're opening that fresh on every request, so how can this run as anything other than root ? > + > + return 0; > +} > +#endif > + > +int main(int argc, char **argv) > +{ > + const char *sopt = "hVk:f:dT:u:g:vq"; > + struct option lopt[] = { > + { "help", no_argument, NULL, 'h' }, > + { "version", no_argument, NULL, 'V' }, > + { "socket", required_argument, NULL, 'k' }, > + { "pidfile", required_argument, NULL, 'f' }, > + { "daemon", no_argument, NULL, 'd' }, > + { "trace", required_argument, NULL, 'T' }, > + { "user", required_argument, NULL, 'u' }, > + { "group", required_argument, NULL, 'g' }, > + { "verbose", no_argument, NULL, 'v' }, > + { NULL, 0, NULL, 0 } > + }; > + int opt_ind = 0; > + int ch; > + Error *local_err = NULL; > + bool daemonize = false; > + bool pidfile_specified = false; > + bool socket_path_specified = false; > + unsigned socket_activation; > + > + struct sigaction sa_sigterm; > + memset(&sa_sigterm, 0, sizeof(sa_sigterm)); > + sa_sigterm.sa_handler = termsig_handler; > + sigaction(SIGTERM, &sa_sigterm, NULL); > + sigaction(SIGINT, &sa_sigterm, NULL); > + sigaction(SIGHUP, &sa_sigterm, NULL); > + > + signal(SIGPIPE, SIG_IGN); > + > + error_init(argv[0]); > + module_call_init(MODULE_INIT_TRACE); > + module_call_init(MODULE_INIT_QOM); > + qemu_add_opts(&qemu_trace_opts); > + qemu_init_exec_dir(argv[0]); > + > + compute_default_paths(); > + > + while ((ch = getopt_long(argc, argv, sopt, lopt, &opt_ind)) != -1) { > + switch (ch) { > + case 'k': > + g_free(socket_path); > + socket_path = g_strdup(optarg); > + socket_path_specified = true; > + if (socket_path[0] != '/') { > + error_report("socket path must be absolute"); > + exit(EXIT_FAILURE); > + } > + break; > + case 'f': > + g_free(pidfile); > + pidfile = g_strdup(optarg); > + pidfile_specified = true; > + break; > +#ifdef CONFIG_LIBCAP_NG > + case 'u': { > + unsigned long res; > + struct passwd *userinfo = getpwnam(optarg); > + if (userinfo) { > + uid = userinfo->pw_uid; > + } else if (qemu_strtoul(optarg, NULL, 10, &res) == 0 && > + (uid_t)res == res) { > + uid = res; > + } else { > + error_report("invalid user '%s'", optarg); > + exit(EXIT_FAILURE); > + } > + break; > + } > + case 'g': { > + unsigned long res; > + struct group *groupinfo = getgrnam(optarg); > + if (groupinfo) { > + gid = groupinfo->gr_gid; > + } else if (qemu_strtoul(optarg, NULL, 10, &res) == 0 && > + (gid_t)res == res) { > + gid = res; > + } else { > + error_report("invalid group '%s'", optarg); > + exit(EXIT_FAILURE); > + } > + break; > + } > +#else > + case 'u': > + case 'g': > + error_report("-%c not supported by this %s", ch, argv[0]); > + exit(1); > +#endif > + case 'd': > + daemonize = true; > + break; > + case 'T': > + trace_opt_parse(optarg); > + break; > + case 'V': > + version(argv[0]); > + exit(EXIT_SUCCESS); > + break; > + case 'h': > + usage(argv[0]); > + exit(EXIT_SUCCESS); > + break; > + case '?': > + error_report("Try `%s --help' for more information.", argv[0]); > + exit(EXIT_FAILURE); > + } > + } > + > + if (!trace_init_backends()) { > + exit(EXIT_FAILURE); > + } > + trace_init_file(); > + qemu_set_log(LOG_TRACE, &error_fatal); > + > + socket_activation = check_socket_activation(); > + if (socket_activation == 0) { > + SocketAddress saddr; > + saddr = (SocketAddress){ > + .type = SOCKET_ADDRESS_TYPE_UNIX, > + .u.q_unix.path = socket_path, > + }; > + server_ioc = qio_channel_socket_new(); > + if (qio_channel_socket_listen_sync(server_ioc, &saddr, > + 1, &local_err) < 0) { > + object_unref(OBJECT(server_ioc)); > + error_report_err(local_err); > + return 1; > + } > + } else { > + /* Using socket activation - check user didn't use -p etc. */ > + if (socket_path_specified) { > + error_report("Unix socket can't be set when \ > + using socket activation"); > + exit(EXIT_FAILURE); > + } > + > + /* Can only listen on a single socket. */ > + if (socket_activation > 1) { > + error_report("%s does not support socket activation \ > + with LISTEN_FDS > 1", > + argv[0]); > + exit(EXIT_FAILURE); > + } > + server_ioc = qio_channel_socket_new_fd(FIRST_SOCKET_ACTIVATION_FD, > + &local_err); > + if (server_ioc == NULL) { > + error_reportf_err(local_err, > + "Failed to use socket activation: "); > + exit(EXIT_FAILURE); > + } > + } > + > + qemu_init_main_loop(&error_fatal); > + > + server_watch = qio_channel_add_watch(QIO_CHANNEL(server_ioc), > + G_IO_IN, > + accept_client, > + NULL, NULL); > + > + if (daemonize) { > + if (daemon(0, 0) < 0) { > + error_report("Failed to daemonize: %s", strerror(errno)); > + exit(EXIT_FAILURE); > + } > + } > + > + if (daemonize || pidfile_specified) { > + qemu_write_pidfile(pidfile, &error_fatal); > + } > + > +#ifdef CONFIG_LIBCAP_NG > + if (drop_privileges() < 0) { > + error_report("Failed to drop privileges: %s", strerror(errno)); > + exit(EXIT_FAILURE); > + } > +#endif > + > + state = RUNNING; > + do { > + main_loop_wait(false); > + if (state == TERMINATE) { > + state = TERMINATING; > + close_server_socket(); > + } > + } while (num_active_sockets > 0); > + > + exit(EXIT_SUCCESS); > +} > diff --git a/tools/i386/rapl-msr-index.h b/tools/i386/rapl-msr-index.h > new file mode 100644 > index 000000000000..9a7118639ae3 > --- /dev/null > +++ b/tools/i386/rapl-msr-index.h > @@ -0,0 +1,28 @@ > +/* > + * Allowed list of MSR for Privileged RAPL MSR helper commands for QEMU > + * > + * Copyright (C) 2023 Red Hat, Inc. <ahari...@redhat.com> > + * > + * Author: Anthony Harivel <ahari...@redhat.com> > + * > + * This program is free software; you can redistribute it and/or modify > + * it under the terms of the GNU General Public License as published by > + * the Free Software Foundation; under version 2 of the License. > + * > + * This program is distributed in the hope that it will be useful, > + * but WITHOUT ANY WARRANTY; without even the implied warranty of > + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the > + * GNU General Public License for more details. > + * > + * You should have received a copy of the GNU General Public License > + * along with this program; if not, see <http://www.gnu.org/licenses/>. > + */ > + > +/* > + * Should stay in sync with the RAPL MSR > + * in target/i386/cpu.h > + */ > +#define MSR_RAPL_POWER_UNIT 0x00000606 > +#define MSR_PKG_POWER_LIMIT 0x00000610 > +#define MSR_PKG_ENERGY_STATUS 0x00000611 > +#define MSR_PKG_POWER_INFO 0x00000614 > -- > 2.43.0 > With regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|