LXR qemu/softmmu/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
  36struct 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
  44const 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 */
  80const 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 */
  89REQUIRE_CLONE_FLAG(CLONE_VM);
  90REQUIRE_CLONE_FLAG(CLONE_FS);
  91REQUIRE_CLONE_FLAG(CLONE_FILES);
  92REQUIRE_CLONE_FLAG(CLONE_SIGHAND);
  93REQUIRE_CLONE_FLAG(CLONE_THREAD);
  94REQUIRE_CLONE_FLAG(CLONE_SYSVSEM);
  95REQUIRE_CLONE_FLAG(CLONE_SETTLS);
  96REQUIRE_CLONE_FLAG(CLONE_PARENT_SETTID);
  97REQUIRE_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 */
 110FORBID_CLONE_FLAG(CLONE_PIDFD);
 111FORBID_CLONE_FLAG(CLONE_PTRACE);
 112FORBID_CLONE_FLAG(CLONE_VFORK);
 113FORBID_CLONE_FLAG(CLONE_PARENT);
 114FORBID_CLONE_FLAG(CLONE_NEWNS);
 115FORBID_CLONE_FLAG(CLONE_UNTRACED);
 116FORBID_CLONE_FLAG(CLONE_NEWCGROUP);
 117FORBID_CLONE_FLAG(CLONE_NEWUTS);
 118FORBID_CLONE_FLAG(CLONE_NEWIPC);
 119FORBID_CLONE_FLAG(CLONE_NEWUSER);
 120FORBID_CLONE_FLAG(CLONE_NEWPID);
 121FORBID_CLONE_FLAG(CLONE_NEWNET);
 122FORBID_CLONE_FLAG(CLONE_IO);
 123
 124
 125static 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
 268static inline __attribute__((unused)) int
 269qemu_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
 279static 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 action = SECCOMP_RET_KILL_PROCESS;
 287
 288            if (qemu_seccomp(SECCOMP_GET_ACTION_AVAIL, 0, &action) == 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
 303static 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    rc = seccomp_attr_set(ctx, SCMP_FLTATR_CTL_TSYNC, 1);
 316    if (rc != 0) {
 317        error_setg_errno(errp, -rc,
 318                         "failed to set seccomp thread synchronization");
 319        goto seccomp_return;
 320    }
 321
 322    for (i = 0; i < ARRAY_SIZE(denylist); i++) {
 323        uint32_t action;
 324        if (!(seccomp_opts & denylist[i].set)) {
 325            continue;
 326        }
 327
 328        action = qemu_seccomp_update_action(denylist[i].action);
 329        rc = seccomp_rule_add_array(ctx, action, denylist[i].num,
 330                                    denylist[i].narg, denylist[i].arg_cmp);
 331        if (rc < 0) {
 332            error_setg_errno(errp, -rc,
 333                             "failed to add seccomp denylist rules");
 334            goto seccomp_return;
 335        }
 336    }
 337
 338    rc = seccomp_load(ctx);
 339    if (rc < 0) {
 340        error_setg_errno(errp, -rc,
 341                         "failed to load seccomp syscall filter in kernel");
 342    }
 343
 344  seccomp_return:
 345    seccomp_release(ctx);
 346    return rc < 0 ? -1 : 0;
 347}
 348
 349int parse_sandbox(void *opaque, QemuOpts *opts, Error **errp)
 350{
 351    if (qemu_opt_get_bool(opts, "enable", false)) {
 352        uint32_t seccomp_opts = QEMU_SECCOMP_SET_DEFAULT
 353                | QEMU_SECCOMP_SET_OBSOLETE;
 354        const char *value = NULL;
 355
 356        value = qemu_opt_get(opts, "obsolete");
 357        if (value) {
 358            if (g_str_equal(value, "allow")) {
 359                seccomp_opts &= ~QEMU_SECCOMP_SET_OBSOLETE;
 360            } else if (g_str_equal(value, "deny")) {
 361                /* this is the default option, this if is here
 362                 * to provide a little bit of consistency for
 363                 * the command line */
 364            } else {
 365                error_setg(errp, "invalid argument for obsolete");
 366                return -1;
 367            }
 368        }
 369
 370        value = qemu_opt_get(opts, "elevateprivileges");
 371        if (value) {
 372            if (g_str_equal(value, "deny")) {
 373                seccomp_opts |= QEMU_SECCOMP_SET_PRIVILEGED;
 374            } else if (g_str_equal(value, "children")) {
 375                seccomp_opts |= QEMU_SECCOMP_SET_PRIVILEGED;
 376
 377                /* calling prctl directly because we're
 378                 * not sure if host has CAP_SYS_ADMIN set*/
 379                if (prctl(PR_SET_NO_NEW_PRIVS, 1)) {
 380                    error_setg(errp, "failed to set no_new_privs aborting");
 381                    return -1;
 382                }
 383            } else if (g_str_equal(value, "allow")) {
 384                /* default value */
 385            } else {
 386                error_setg(errp, "invalid argument for elevateprivileges");
 387                return -1;
 388            }
 389        }
 390
 391        value = qemu_opt_get(opts, "spawn");
 392        if (value) {
 393            if (g_str_equal(value, "deny")) {
 394                seccomp_opts |= QEMU_SECCOMP_SET_SPAWN;
 395            } else if (g_str_equal(value, "allow")) {
 396                /* default value */
 397            } else {
 398                error_setg(errp, "invalid argument for spawn");
 399                return -1;
 400            }
 401        }
 402
 403        value = qemu_opt_get(opts, "resourcecontrol");
 404        if (value) {
 405            if (g_str_equal(value, "deny")) {
 406                seccomp_opts |= QEMU_SECCOMP_SET_RESOURCECTL;
 407            } else if (g_str_equal(value, "allow")) {
 408                /* default value */
 409            } else {
 410                error_setg(errp, "invalid argument for resourcecontrol");
 411                return -1;
 412            }
 413        }
 414
 415        if (seccomp_start(seccomp_opts, errp) < 0) {
 416            return -1;
 417        }
 418    }
 419
 420    return 0;
 421}
 422
 423static QemuOptsList qemu_sandbox_opts = {
 424    .name = "sandbox",
 425    .implied_opt_name = "enable",
 426    .head = QTAILQ_HEAD_INITIALIZER(qemu_sandbox_opts.head),
 427    .desc = {
 428        {
 429            .name = "enable",
 430            .type = QEMU_OPT_BOOL,
 431        },
 432        {
 433            .name = "obsolete",
 434            .type = QEMU_OPT_STRING,
 435        },
 436        {
 437            .name = "elevateprivileges",
 438            .type = QEMU_OPT_STRING,
 439        },
 440        {
 441            .name = "spawn",
 442            .type = QEMU_OPT_STRING,
 443        },
 444        {
 445            .name = "resourcecontrol",
 446            .type = QEMU_OPT_STRING,
 447        },
 448        { /* end of list */ }
 449    },
 450};
 451
 452static void seccomp_register(void)
 453{
 454    bool add = false;
 455
 456    /* FIXME: use seccomp_api_get() >= 2 check when released */
 457
 458#if defined(SECCOMP_FILTER_FLAG_TSYNC)
 459    int check;
 460
 461    /* check host TSYNC capability, it returns errno == ENOSYS if unavailable */
 462    check = qemu_seccomp(SECCOMP_SET_MODE_FILTER,
 463                         SECCOMP_FILTER_FLAG_TSYNC, NULL);
 464    if (check < 0 && errno == EFAULT) {
 465        add = true;
 466    }
 467#endif
 468
 469    if (add) {
 470        qemu_add_opts(&qemu_sandbox_opts);
 471    }
 472}
 473opts_init(seccomp_register);
 474