system/qemu-seccomp.c

   1 /*
   2  * QEMU seccomp mode 2 support with libseccomp
   3  *
   4  * Copyright IBM, Corp. 2012
   5  *
   6  * Authors:
   7  *  Eduardo Otubo    <eotubo@br.ibm.com>
   8  *
   9  * This work is licensed under the terms of the GNU GPL, version 2.  See
  10  * the COPYING file in the top-level directory.
  11  *
  12  * Contributions after 2012-01-13 are licensed under the terms of the
  13  * GNU GPL, version 2 or (at your option) any later version.
  14  */
  15
  16 #include "qemu/osdep.h"
  17 #include "qapi/error.h"
  18 #include "qemu/config-file.h"
  19 #include "qemu/option.h"
  20 #include "qemu/module.h"
  21 #include <sys/prctl.h>
  22 #include <seccomp.h>
  23 #include "sysemu/seccomp.h"
  24 #include <linux/seccomp.h>
  25
  26 /* For some architectures (notably ARM) cacheflush is not supported until
  27  * libseccomp 2.2.3, but configure enforces that we are using a more recent
  28  * version on those hosts, so it is OK for this check to be less strict.
  29  */
  30 #if SCMP_VER_MAJOR >= 3
  31   #define HAVE_CACHEFLUSH
  32 #elif SCMP_VER_MAJOR == 2 && SCMP_VER_MINOR >= 2
  33   #define HAVE_CACHEFLUSH
  34 #endif
  35
  36 struct QemuSeccompSyscall {
  37     int32_t num;
  38     uint8_t set;
  39     uint8_t narg;
  40     const struct scmp_arg_cmp *arg_cmp;
  41     uint32_t action;
  42 };
  43
  44 const struct scmp_arg_cmp sched_setscheduler_arg[] = {
  45     /* was SCMP_A1(SCMP_CMP_NE, SCHED_IDLE), but expanded due to GCC 4.x bug */
  46     { .arg = 1, .op = SCMP_CMP_NE, .datum_a = SCHED_IDLE }
  47 };
  48
  49 /*
  50  * See 'NOTES' in 'man 2 clone' - s390 & cross have 'flags' in
  51  *  different position to other architectures
  52  */
  53 #if defined(HOST_S390X) || defined(HOST_S390) || defined(HOST_CRIS)
  54 #define CLONE_FLAGS_ARG 1
  55 #else
  56 #define CLONE_FLAGS_ARG 0
  57 #endif
  58
  59 #ifndef CLONE_PIDFD
  60 # define CLONE_PIDFD 0x00001000
  61 #endif
  62
  63 #define REQUIRE_CLONE_FLAG(flag) \
  64     const struct scmp_arg_cmp clone_arg ## flag[] = { \
  65     { .arg = CLONE_FLAGS_ARG, \
  66       .op = SCMP_CMP_MASKED_EQ, \
  67       .datum_a = flag, .datum_b = 0 } }
  68
  69 #define FORBID_CLONE_FLAG(flag) \
  70     const struct scmp_arg_cmp clone_arg ## flag[] = { \
  71     { .arg = CLONE_FLAGS_ARG, \
  72       .op = SCMP_CMP_MASKED_EQ, \
  73       .datum_a = flag, .datum_b = flag } }
  74
  75 #define RULE_CLONE_FLAG(flag) \
  76     { SCMP_SYS(clone),                  QEMU_SECCOMP_SET_SPAWN, \
  77       ARRAY_SIZE(clone_arg ## flag), clone_arg ## flag, SCMP_ACT_TRAP }
  78
  79 /* If no CLONE_* flags are set, except CSIGNAL, deny */
  80 const struct scmp_arg_cmp clone_arg_none[] = {
  81     { .arg = CLONE_FLAGS_ARG,
  82       .op = SCMP_CMP_MASKED_EQ,
  83       .datum_a = ~(CSIGNAL), .datum_b = 0 }
  84 };
  85
  86 /*
  87  * pthread_create should always set all of these.
  88  */
  89 REQUIRE_CLONE_FLAG(CLONE_VM);
  90 REQUIRE_CLONE_FLAG(CLONE_FS);
  91 REQUIRE_CLONE_FLAG(CLONE_FILES);
  92 REQUIRE_CLONE_FLAG(CLONE_SIGHAND);
  93 REQUIRE_CLONE_FLAG(CLONE_THREAD);
  94 REQUIRE_CLONE_FLAG(CLONE_SYSVSEM);
  95 REQUIRE_CLONE_FLAG(CLONE_SETTLS);
  96 REQUIRE_CLONE_FLAG(CLONE_PARENT_SETTID);
  97 REQUIRE_CLONE_FLAG(CLONE_CHILD_CLEARTID);
  98 /*
  99  * Musl sets this in pthread_create too, but it is
 100  * obsolete and harmless since its behaviour is
 101  * subsumed under CLONE_THREAD
 102  */
 103 /*REQUIRE_CLONE_FLAG(CLONE_DETACHED);*/
 104
 105
 106 /*
 107  * These all indicate an attempt to spawn a process
 108  * instead of a thread, or other undesirable scenarios
 109  */
 110 FORBID_CLONE_FLAG(CLONE_PIDFD);
 111 FORBID_CLONE_FLAG(CLONE_PTRACE);
 112 FORBID_CLONE_FLAG(CLONE_VFORK);
 113 FORBID_CLONE_FLAG(CLONE_PARENT);
 114 FORBID_CLONE_FLAG(CLONE_NEWNS);
 115 FORBID_CLONE_FLAG(CLONE_UNTRACED);
 116 FORBID_CLONE_FLAG(CLONE_NEWCGROUP);
 117 FORBID_CLONE_FLAG(CLONE_NEWUTS);
 118 FORBID_CLONE_FLAG(CLONE_NEWIPC);
 119 FORBID_CLONE_FLAG(CLONE_NEWUSER);
 120 FORBID_CLONE_FLAG(CLONE_NEWPID);
 121 FORBID_CLONE_FLAG(CLONE_NEWNET);
 122 FORBID_CLONE_FLAG(CLONE_IO);
 123
 124
 125 static const struct QemuSeccompSyscall denylist[] = {
 126     /* default set of syscalls that should get blocked */
 127     { SCMP_SYS(reboot),                 QEMU_SECCOMP_SET_DEFAULT,
 128       0, NULL, SCMP_ACT_TRAP },
 129     { SCMP_SYS(swapon),                 QEMU_SECCOMP_SET_DEFAULT,
 130       0, NULL, SCMP_ACT_TRAP },
 131     { SCMP_SYS(swapoff),                QEMU_SECCOMP_SET_DEFAULT,
 132       0, NULL, SCMP_ACT_TRAP },
 133     { SCMP_SYS(syslog),                 QEMU_SECCOMP_SET_DEFAULT,
 134       0, NULL, SCMP_ACT_TRAP },
 135     { SCMP_SYS(mount),                  QEMU_SECCOMP_SET_DEFAULT,
 136       0, NULL, SCMP_ACT_TRAP },
 137     { SCMP_SYS(umount),                 QEMU_SECCOMP_SET_DEFAULT,
 138       0, NULL, SCMP_ACT_TRAP },
 139     { SCMP_SYS(kexec_load),             QEMU_SECCOMP_SET_DEFAULT,
 140       0, NULL, SCMP_ACT_TRAP },
 141     { SCMP_SYS(afs_syscall),            QEMU_SECCOMP_SET_DEFAULT,
 142       0, NULL, SCMP_ACT_TRAP },
 143     { SCMP_SYS(break),                  QEMU_SECCOMP_SET_DEFAULT,
 144       0, NULL, SCMP_ACT_TRAP },
 145     { SCMP_SYS(ftime),                  QEMU_SECCOMP_SET_DEFAULT,
 146       0, NULL, SCMP_ACT_TRAP },
 147     { SCMP_SYS(getpmsg),                QEMU_SECCOMP_SET_DEFAULT,
 148       0, NULL, SCMP_ACT_TRAP },
 149     { SCMP_SYS(gtty),                   QEMU_SECCOMP_SET_DEFAULT,
 150       0, NULL, SCMP_ACT_TRAP },
 151     { SCMP_SYS(lock),                   QEMU_SECCOMP_SET_DEFAULT,
 152       0, NULL, SCMP_ACT_TRAP },
 153     { SCMP_SYS(mpx),                    QEMU_SECCOMP_SET_DEFAULT,
 154       0, NULL, SCMP_ACT_TRAP },
 155     { SCMP_SYS(prof),                   QEMU_SECCOMP_SET_DEFAULT,
 156       0, NULL, SCMP_ACT_TRAP },
 157     { SCMP_SYS(profil),                 QEMU_SECCOMP_SET_DEFAULT,
 158       0, NULL, SCMP_ACT_TRAP },
 159     { SCMP_SYS(putpmsg),                QEMU_SECCOMP_SET_DEFAULT,
 160       0, NULL, SCMP_ACT_TRAP },
 161     { SCMP_SYS(security),               QEMU_SECCOMP_SET_DEFAULT,
 162       0, NULL, SCMP_ACT_TRAP },
 163     { SCMP_SYS(stty),                   QEMU_SECCOMP_SET_DEFAULT,
 164       0, NULL, SCMP_ACT_TRAP },
 165     { SCMP_SYS(tuxcall),                QEMU_SECCOMP_SET_DEFAULT,
 166       0, NULL, SCMP_ACT_TRAP },
 167     { SCMP_SYS(ulimit),                 QEMU_SECCOMP_SET_DEFAULT,
 168       0, NULL, SCMP_ACT_TRAP },
 169     { SCMP_SYS(vserver),                QEMU_SECCOMP_SET_DEFAULT,
 170       0, NULL, SCMP_ACT_TRAP },
 171     /* obsolete */
 172     { SCMP_SYS(readdir),                QEMU_SECCOMP_SET_OBSOLETE,
 173       0, NULL, SCMP_ACT_TRAP },
 174     { SCMP_SYS(_sysctl),                QEMU_SECCOMP_SET_OBSOLETE,
 175       0, NULL, SCMP_ACT_TRAP },
 176     { SCMP_SYS(bdflush),                QEMU_SECCOMP_SET_OBSOLETE,
 177       0, NULL, SCMP_ACT_TRAP },
 178     { SCMP_SYS(create_module),          QEMU_SECCOMP_SET_OBSOLETE,
 179       0, NULL, SCMP_ACT_TRAP },
 180     { SCMP_SYS(get_kernel_syms),        QEMU_SECCOMP_SET_OBSOLETE,
 181       0, NULL, SCMP_ACT_TRAP },
 182     { SCMP_SYS(query_module),           QEMU_SECCOMP_SET_OBSOLETE,
 183       0, NULL, SCMP_ACT_TRAP },
 184     { SCMP_SYS(sgetmask),               QEMU_SECCOMP_SET_OBSOLETE,
 185       0, NULL, SCMP_ACT_TRAP },
 186     { SCMP_SYS(ssetmask),               QEMU_SECCOMP_SET_OBSOLETE,
 187       0, NULL, SCMP_ACT_TRAP },
 188     { SCMP_SYS(sysfs),                  QEMU_SECCOMP_SET_OBSOLETE,
 189       0, NULL, SCMP_ACT_TRAP },
 190     { SCMP_SYS(uselib),                 QEMU_SECCOMP_SET_OBSOLETE,
 191       0, NULL, SCMP_ACT_TRAP },
 192     { SCMP_SYS(ustat),                  QEMU_SECCOMP_SET_OBSOLETE,
 193       0, NULL, SCMP_ACT_TRAP },
 194     /* privileged */
 195     { SCMP_SYS(setuid),                 QEMU_SECCOMP_SET_PRIVILEGED,
 196       0, NULL, SCMP_ACT_TRAP },
 197     { SCMP_SYS(setgid),                 QEMU_SECCOMP_SET_PRIVILEGED,
 198       0, NULL, SCMP_ACT_TRAP },
 199     { SCMP_SYS(setpgid),                QEMU_SECCOMP_SET_PRIVILEGED,
 200       0, NULL, SCMP_ACT_TRAP },
 201     { SCMP_SYS(setsid),                 QEMU_SECCOMP_SET_PRIVILEGED,
 202       0, NULL, SCMP_ACT_TRAP },
 203     { SCMP_SYS(setreuid),               QEMU_SECCOMP_SET_PRIVILEGED,
 204       0, NULL, SCMP_ACT_TRAP },
 205     { SCMP_SYS(setregid),               QEMU_SECCOMP_SET_PRIVILEGED,
 206       0, NULL, SCMP_ACT_TRAP },
 207     { SCMP_SYS(setresuid),              QEMU_SECCOMP_SET_PRIVILEGED,
 208       0, NULL, SCMP_ACT_TRAP },
 209     { SCMP_SYS(setresgid),              QEMU_SECCOMP_SET_PRIVILEGED,
 210       0, NULL, SCMP_ACT_TRAP },
 211     { SCMP_SYS(setfsuid),               QEMU_SECCOMP_SET_PRIVILEGED,
 212       0, NULL, SCMP_ACT_TRAP },
 213     { SCMP_SYS(setfsgid),               QEMU_SECCOMP_SET_PRIVILEGED,
 214       0, NULL, SCMP_ACT_TRAP },
 215     /* spawn */
 216     { SCMP_SYS(fork),                   QEMU_SECCOMP_SET_SPAWN,
 217       0, NULL, SCMP_ACT_TRAP },
 218     { SCMP_SYS(vfork),                  QEMU_SECCOMP_SET_SPAWN,
 219       0, NULL, SCMP_ACT_TRAP },
 220     { SCMP_SYS(execve),                 QEMU_SECCOMP_SET_SPAWN,
 221       0, NULL, SCMP_ACT_TRAP },
 222     { SCMP_SYS(clone),                  QEMU_SECCOMP_SET_SPAWN,
 223       ARRAY_SIZE(clone_arg_none), clone_arg_none, SCMP_ACT_TRAP },
 224     RULE_CLONE_FLAG(CLONE_VM),
 225     RULE_CLONE_FLAG(CLONE_FS),
 226     RULE_CLONE_FLAG(CLONE_FILES),
 227     RULE_CLONE_FLAG(CLONE_SIGHAND),
 228     RULE_CLONE_FLAG(CLONE_THREAD),
 229     RULE_CLONE_FLAG(CLONE_SYSVSEM),
 230     RULE_CLONE_FLAG(CLONE_SETTLS),
 231     RULE_CLONE_FLAG(CLONE_PARENT_SETTID),
 232     RULE_CLONE_FLAG(CLONE_CHILD_CLEARTID),
 233     /*RULE_CLONE_FLAG(CLONE_DETACHED),*/
 234     RULE_CLONE_FLAG(CLONE_PIDFD),
 235     RULE_CLONE_FLAG(CLONE_PTRACE),
 236     RULE_CLONE_FLAG(CLONE_VFORK),
 237     RULE_CLONE_FLAG(CLONE_PARENT),
 238     RULE_CLONE_FLAG(CLONE_NEWNS),
 239     RULE_CLONE_FLAG(CLONE_UNTRACED),
 240     RULE_CLONE_FLAG(CLONE_NEWCGROUP),
 241     RULE_CLONE_FLAG(CLONE_NEWUTS),
 242     RULE_CLONE_FLAG(CLONE_NEWIPC),
 243     RULE_CLONE_FLAG(CLONE_NEWUSER),
 244     RULE_CLONE_FLAG(CLONE_NEWPID),
 245     RULE_CLONE_FLAG(CLONE_NEWNET),
 246     RULE_CLONE_FLAG(CLONE_IO),
 247 #ifdef __SNR_clone3
 248     { SCMP_SYS(clone3),                 QEMU_SECCOMP_SET_SPAWN,
 249       0, NULL, SCMP_ACT_ERRNO(ENOSYS) },
 250 #endif
 251 #ifdef __SNR_execveat
 252     { SCMP_SYS(execveat),               QEMU_SECCOMP_SET_SPAWN },
 253 #endif
 254     { SCMP_SYS(setns),                  QEMU_SECCOMP_SET_SPAWN },
 255     { SCMP_SYS(unshare),                QEMU_SECCOMP_SET_SPAWN },
 256     /* resource control */
 257     { SCMP_SYS(setpriority),            QEMU_SECCOMP_SET_RESOURCECTL,
 258       0, NULL, SCMP_ACT_ERRNO(EPERM) },
 259     { SCMP_SYS(sched_setparam),         QEMU_SECCOMP_SET_RESOURCECTL,
 260       0, NULL, SCMP_ACT_ERRNO(EPERM) },
 261     { SCMP_SYS(sched_setscheduler),     QEMU_SECCOMP_SET_RESOURCECTL,
 262       ARRAY_SIZE(sched_setscheduler_arg), sched_setscheduler_arg,
 263       SCMP_ACT_ERRNO(EPERM) },
 264     { SCMP_SYS(sched_setaffinity),      QEMU_SECCOMP_SET_RESOURCECTL,
 265       0, NULL, SCMP_ACT_ERRNO(EPERM) },
 266 };
 267
 268 static inline __attribute__((unused)) int
 269 qemu_seccomp(unsigned int operation, unsigned int flags, void *args)
 270 {
 271 #ifdef __NR_seccomp
 272     return syscall(__NR_seccomp, operation, flags, args);
 273 #else
 274     errno = ENOSYS;
 275     return -1;
 276 #endif
 277 }
 278
 279 static uint32_t qemu_seccomp_update_action(uint32_t action)
 280 {
 281 #if defined(SECCOMP_GET_ACTION_AVAIL) && defined(SCMP_ACT_KILL_PROCESS) && \
 282     defined(SECCOMP_RET_KILL_PROCESS)
 283     if (action == SCMP_ACT_TRAP) {
 284         static int kill_process = -1;
 285         if (kill_process == -1) {
 286             uint32_t testaction = SECCOMP_RET_KILL_PROCESS;
 287
 288             if (qemu_seccomp(SECCOMP_GET_ACTION_AVAIL, 0, &testaction) == 0) {
 289                 kill_process = 1;
 290             } else {
 291                 kill_process = 0;
 292             }
 293         }
 294         if (kill_process == 1) {
 295             return SCMP_ACT_KILL_PROCESS;
 296         }
 297     }
 298 #endif
 299     return action;
 300 }
 301
 302
 303 static int seccomp_start(uint32_t seccomp_opts, Error **errp)
 304 {
 305     int rc = -1;
 306     unsigned int i = 0;
 307     scmp_filter_ctx ctx;
 308
 309     ctx = seccomp_init(SCMP_ACT_ALLOW);
 310     if (ctx == NULL) {
 311         error_setg(errp, "failed to initialize seccomp context");
 312         goto seccomp_return;
 313     }
 314
 315 #if defined(CONFIG_SECCOMP_SYSRAWRC)
 316     /*
 317      * This must be the first seccomp_attr_set() call to have full
 318      * error propagation from subsequent seccomp APIs.
 319      */
 320     rc = seccomp_attr_set(ctx, SCMP_FLTATR_API_SYSRAWRC, 1);
 321     if (rc != 0) {
 322         error_setg_errno(errp, -rc,
 323                          "failed to set seccomp rawrc attribute");
 324         goto seccomp_return;
 325     }
 326 #endif
 327
 328     rc = seccomp_attr_set(ctx, SCMP_FLTATR_CTL_TSYNC, 1);
 329     if (rc != 0) {
 330         error_setg_errno(errp, -rc,
 331                          "failed to set seccomp thread synchronization");
 332         goto seccomp_return;
 333     }
 334
 335     for (i = 0; i < ARRAY_SIZE(denylist); i++) {
 336         uint32_t action;
 337         if (!(seccomp_opts & denylist[i].set)) {
 338             continue;
 339         }
 340
 341         action = qemu_seccomp_update_action(denylist[i].action);
 342         rc = seccomp_rule_add_array(ctx, action, denylist[i].num,
 343                                     denylist[i].narg, denylist[i].arg_cmp);
 344         if (rc < 0) {
 345             error_setg_errno(errp, -rc,
 346                              "failed to add seccomp denylist rules");
 347             goto seccomp_return;
 348         }
 349     }
 350
 351     rc = seccomp_load(ctx);
 352     if (rc < 0) {
 353         error_setg_errno(errp, -rc,
 354                          "failed to load seccomp syscall filter in kernel");
 355     }
 356
 357   seccomp_return:
 358     seccomp_release(ctx);
 359     return rc < 0 ? -1 : 0;
 360 }
 361
 362 int parse_sandbox(void *opaque, QemuOpts *opts, Error **errp)
 363 {
 364     if (qemu_opt_get_bool(opts, "enable", false)) {
 365         uint32_t seccomp_opts = QEMU_SECCOMP_SET_DEFAULT
 366                 | QEMU_SECCOMP_SET_OBSOLETE;
 367         const char *value = NULL;
 368
 369         value = qemu_opt_get(opts, "obsolete");
 370         if (value) {
 371             if (g_str_equal(value, "allow")) {
 372                 seccomp_opts &= ~QEMU_SECCOMP_SET_OBSOLETE;
 373             } else if (g_str_equal(value, "deny")) {
 374                 /* this is the default option, this if is here
 375                  * to provide a little bit of consistency for
 376                  * the command line */
 377             } else {
 378                 error_setg(errp, "invalid argument for obsolete");
 379                 return -1;
 380             }
 381         }
 382
 383         value = qemu_opt_get(opts, "elevateprivileges");
 384         if (value) {
 385             if (g_str_equal(value, "deny")) {
 386                 seccomp_opts |= QEMU_SECCOMP_SET_PRIVILEGED;
 387             } else if (g_str_equal(value, "children")) {
 388                 seccomp_opts |= QEMU_SECCOMP_SET_PRIVILEGED;
 389
 390                 /* calling prctl directly because we're
 391                  * not sure if host has CAP_SYS_ADMIN set*/
 392                 if (prctl(PR_SET_NO_NEW_PRIVS, 1)) {
 393                     error_setg(errp, "failed to set no_new_privs aborting");
 394                     return -1;
 395                 }
 396             } else if (g_str_equal(value, "allow")) {
 397                 /* default value */
 398             } else {
 399                 error_setg(errp, "invalid argument for elevateprivileges");
 400                 return -1;
 401             }
 402         }
 403
 404         value = qemu_opt_get(opts, "spawn");
 405         if (value) {
 406             if (g_str_equal(value, "deny")) {
 407                 seccomp_opts |= QEMU_SECCOMP_SET_SPAWN;
 408             } else if (g_str_equal(value, "allow")) {
 409                 /* default value */
 410             } else {
 411                 error_setg(errp, "invalid argument for spawn");
 412                 return -1;
 413             }
 414         }
 415
 416         value = qemu_opt_get(opts, "resourcecontrol");
 417         if (value) {
 418             if (g_str_equal(value, "deny")) {
 419                 seccomp_opts |= QEMU_SECCOMP_SET_RESOURCECTL;
 420             } else if (g_str_equal(value, "allow")) {
 421                 /* default value */
 422             } else {
 423                 error_setg(errp, "invalid argument for resourcecontrol");
 424                 return -1;
 425             }
 426         }
 427
 428         if (seccomp_start(seccomp_opts, errp) < 0) {
 429             return -1;
 430         }
 431     }
 432
 433     return 0;
 434 }
 435
 436 static QemuOptsList qemu_sandbox_opts = {
 437     .name = "sandbox",
 438     .implied_opt_name = "enable",
 439     .head = QTAILQ_HEAD_INITIALIZER(qemu_sandbox_opts.head),
 440     .desc = {
 441         {
 442             .name = "enable",
 443             .type = QEMU_OPT_BOOL,
 444         },
 445         {
 446             .name = "obsolete",
 447             .type = QEMU_OPT_STRING,
 448         },
 449         {
 450             .name = "elevateprivileges",
 451             .type = QEMU_OPT_STRING,
 452         },
 453         {
 454             .name = "spawn",
 455             .type = QEMU_OPT_STRING,
 456         },
 457         {
 458             .name = "resourcecontrol",
 459             .type = QEMU_OPT_STRING,
 460         },
 461         { /* end of list */ }
 462     },
 463 };
 464
 465 static void seccomp_register(void)
 466 {
 467     bool add = false;
 468
 469     /* FIXME: use seccomp_api_get() >= 2 check when released */
 470
 471 #if defined(SECCOMP_FILTER_FLAG_TSYNC)
 472     int check;
 473
 474     /* check host TSYNC capability, it returns errno == ENOSYS if unavailable */
 475     check = qemu_seccomp(SECCOMP_SET_MODE_FILTER,
 476                          SECCOMP_FILTER_FLAG_TSYNC, NULL);
 477     if (check < 0 && errno == EFAULT) {
 478         add = true;
 479     }
 480 #endif
 481
 482     if (add) {
 483         qemu_add_opts(&qemu_sandbox_opts);
 484     }
 485 }
 486 opts_init(seccomp_register);