On Tue, Oct 31, 2023 at 03:46:02PM +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."
>
> Signed-off-by: Anthony Harivel <ahari...@redhat.com>
> ---
> 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 ++
Missing .service and .socket unit files needed for systemd integration.
See those present for qemu-pr-helper for examples
> 5 files changed, 630 insertions(+)
> 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/tools/i386/qemu-vmsr-helper.c b/tools/i386/qemu-vmsr-helper.c
> new file mode 100644
> index 000000000000..1d82a2753e44
> --- /dev/null
> +++ b/tools/i386/qemu-vmsr-helper.c
> +#define MAX_PATH_LEN 50
> +#define MAX_LINE_LEN 500
> +#define PR_OUT_FIXED_PARAM_SIZE 24
These latter two constants are not used.
> +
> +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;
> +static int noisy;
> +static int verbose;
> +
> +#ifdef CONFIG_LIBCAP_NG
> +static int uid = -1;
> +static int gid = -1;
> +#endif
> +
> +static void compute_default_paths(void)
> +{
> + g_autofree char *state = qemu_get_local_state_dir();
> +
> + socket_path = g_build_filename(state, "run", "qemu-vmsr-helper.sock",
> NULL);
> + pidfile = g_build_filename(state, "run", "qemu-vmsr-helper.pid", NULL);
> +}
> +
> +/*
> + * Check if the TID that request the MSR read
> + * belongs to the peer. It should a TID of a vCPU.
> + */
> +static bool is_tid_present(pid_t pid, pid_t tid)
> +{
> + char pidStr[20];
> + char tidStr[20];
> +
> + snprintf(pidStr, sizeof(pidStr), "%d", pid);
> + snprintf(tidStr, sizeof(tidStr), "%d", tid);
g_strdup_printf() not an unchecked static buffer.
> +
> + char pidPath[256];
> + char tidPath[256];
> +
> + snprintf(pidPath, sizeof(pidPath), "/proc/%s", pidStr);
You never read this variable once built
> + snprintf(tidPath, sizeof(tidPath), "/proc/%s/task/%s", pidStr, tidStr);
g_build_file_name
> +
> + /* Check if the TID directory exists within the PID directory */
> + if (access(tidPath, F_OK) == 0) {
> + return true;
> + }
> +
> + return false;
> +}
> +static uint64_t vmsr_read_msr(uint32_t reg, unsigned int cpu_id)
> +{
> + int fd;
> + uint64_t data;
> +
> + char path[MAX_PATH_LEN];
> + snprintf(path, MAX_PATH_LEN, "/dev/cpu/%u/msr", cpu_id);
g_strdup_printf
> +
> + fd = open(path , O_RDONLY);
> + if (fd < 0) {
> + return 0;
> + }
> + if (pread(fd, &data, sizeof data, reg) != sizeof data) {
> + data = 0;
> + }
> +
> + close(fd);
> + return data;
> +}
> +
> +static void usage(const char *name)
> +{
> + (printf) (
> +"Usage: %s [OPTIONS] FILE\n"
> +"Virtual RAPL MSR helper program for QEMU\n"
> +"\n"
> +" -h, --help display this help and exit\n"
> +" -V, --version output version information and exit\n"
> +"\n"
> +" -d, --daemon run in the background\n"
> +" -f, --pidfile=PATH PID file when running as a daemon\n"
> +" (default '%s')\n"
> +" -k, --socket=PATH path to the unix socket\n"
> +" (default '%s')\n"
> +" -T, --trace [[enable=]<pattern>][,events=<file>][,file=<file>]\n"
> +" specify tracing options\n"
> +#ifdef CONFIG_LIBCAP_NG
> +" -u, --user=USER user to drop privileges to\n"
> +" -g, --group=GROUP group to drop privileges to\n"
> +#endif
> +"\n"
> +QEMU_HELP_BOTTOM "\n"
> + , name, pidfile, socket_path);
> +}
> +
> +static void version(const char *name)
> +{
> + printf(
> +"%s " QEMU_FULL_VERSION "\n"
> +"Written by Anthony Harivel.\n"
> +"\n"
> +QEMU_COPYRIGHT "\n"
> +"This is free software; see the source for copying conditions. There is
> NO\n"
> +"warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR
> PURPOSE.\n"
> + , name);
> +}
> +
> +typedef struct VMSRHelperClient {
> + QIOChannelSocket *ioc;
> + Coroutine *co;
> + int fd;
This FD field is set to -1 and never changed / read thereafter AFAICS,
so please remove it.
> +} VMSRHelperClient;
> +
> +static void coroutine_fn vh_co_entry(void *opaque)
> +{
> + VMSRHelperClient *client = opaque;
> + uint64_t vmsr;
> + uint32_t request[3];
> + struct ucred cred;
> + 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
> + * Only QEMU PID/TID are allowed
> + */
> + qio_channel_get_peercred(QIO_CHANNEL(client->ioc), &cred, &local_err);
> +
> + if (cred.pid == 0) {
> + if (local_err != NULL) {
> + error_report_err(local_err);
> + }
> + error_report("Failed to get peer credentials");
> + 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), NULL);
The 'NULL' should be &local_err, so that the next error_report
line actually gives a useful error message with actual details.
> + if (!is_msr_allowed(request[0]) || r < 0) {
request[0] is accessing uninitialized memory in case that r < 0.
You must check for errors first.
> + error_report("Read request fail: %d, %d", request[0], request[1]);
use error_report_err in the 'r < 0' case.
> + goto out;
> + }
> +
> + vmsr = vmsr_read_msr(request[0], request[1]);
> +
> + if (!is_tid_present(cred.pid, request[2])) {
> + error_report("requested TID not in peer PID");
> + vmsr = 0;
> + }
> +
> + r = qio_channel_write_all(QIO_CHANNEL(client->ioc),
> + (char *) &vmsr, sizeof(vmsr), NULL);
Again you must pass &local_err...
> + if (r < 0) {
> + error_report("write vmsr failed");
and use error_report_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->fd = -1;
> + 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;
> + }
> +
> + 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' },
> + { "quiet", no_argument, NULL, 'q' },
> + { NULL, 0, NULL, 0 }
> + };
> + int opt_ind = 0;
> + int loglevel = 1;
> + int quiet = 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 'q':
> + quiet = 1;
> + break;
> + case 'v':
> + ++loglevel;
> + 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);
> + }
> + }
> +
> + /* set verbosity */
> + noisy = !quiet && (loglevel >= 3);
> + verbose = quiet ? 0 : MIN(loglevel, 3);
AFAIK nothing ever uses the noisy or verbose flags, so please remove
them or use them.
> +
> + if (!trace_init_backends()) {
> + exit(EXIT_FAILURE);
> + }
> + trace_init_file();
> + qemu_set_log(LOG_TRACE, &error_fatal);
With regards,
Daniel
--
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