LXR qemu/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};
  42
  43const struct scmp_arg_cmp sched_setscheduler_arg[] = {
  44    SCMP_A1(SCMP_CMP_NE, SCHED_IDLE)
  45};
  46
  47static const struct QemuSeccompSyscall blacklist[] = {
  48    /* default set of syscalls to blacklist */
  49    { SCMP_SYS(reboot),                 QEMU_SECCOMP_SET_DEFAULT },
  50    { SCMP_SYS(swapon),                 QEMU_SECCOMP_SET_DEFAULT },
  51    { SCMP_SYS(swapoff),                QEMU_SECCOMP_SET_DEFAULT },
  52    { SCMP_SYS(syslog),                 QEMU_SECCOMP_SET_DEFAULT },
  53    { SCMP_SYS(mount),                  QEMU_SECCOMP_SET_DEFAULT },
  54    { SCMP_SYS(umount),                 QEMU_SECCOMP_SET_DEFAULT },
  55    { SCMP_SYS(kexec_load),             QEMU_SECCOMP_SET_DEFAULT },
  56    { SCMP_SYS(afs_syscall),            QEMU_SECCOMP_SET_DEFAULT },
  57    { SCMP_SYS(break),                  QEMU_SECCOMP_SET_DEFAULT },
  58    { SCMP_SYS(ftime),                  QEMU_SECCOMP_SET_DEFAULT },
  59    { SCMP_SYS(getpmsg),                QEMU_SECCOMP_SET_DEFAULT },
  60    { SCMP_SYS(gtty),                   QEMU_SECCOMP_SET_DEFAULT },
  61    { SCMP_SYS(lock),                   QEMU_SECCOMP_SET_DEFAULT },
  62    { SCMP_SYS(mpx),                    QEMU_SECCOMP_SET_DEFAULT },
  63    { SCMP_SYS(prof),                   QEMU_SECCOMP_SET_DEFAULT },
  64    { SCMP_SYS(profil),                 QEMU_SECCOMP_SET_DEFAULT },
  65    { SCMP_SYS(putpmsg),                QEMU_SECCOMP_SET_DEFAULT },
  66    { SCMP_SYS(security),               QEMU_SECCOMP_SET_DEFAULT },
  67    { SCMP_SYS(stty),                   QEMU_SECCOMP_SET_DEFAULT },
  68    { SCMP_SYS(tuxcall),                QEMU_SECCOMP_SET_DEFAULT },
  69    { SCMP_SYS(ulimit),                 QEMU_SECCOMP_SET_DEFAULT },
  70    { SCMP_SYS(vserver),                QEMU_SECCOMP_SET_DEFAULT },
  71    /* obsolete */
  72    { SCMP_SYS(readdir),                QEMU_SECCOMP_SET_OBSOLETE },
  73    { SCMP_SYS(_sysctl),                QEMU_SECCOMP_SET_OBSOLETE },
  74    { SCMP_SYS(bdflush),                QEMU_SECCOMP_SET_OBSOLETE },
  75    { SCMP_SYS(create_module),          QEMU_SECCOMP_SET_OBSOLETE },
  76    { SCMP_SYS(get_kernel_syms),        QEMU_SECCOMP_SET_OBSOLETE },
  77    { SCMP_SYS(query_module),           QEMU_SECCOMP_SET_OBSOLETE },
  78    { SCMP_SYS(sgetmask),               QEMU_SECCOMP_SET_OBSOLETE },
  79    { SCMP_SYS(ssetmask),               QEMU_SECCOMP_SET_OBSOLETE },
  80    { SCMP_SYS(sysfs),                  QEMU_SECCOMP_SET_OBSOLETE },
  81    { SCMP_SYS(uselib),                 QEMU_SECCOMP_SET_OBSOLETE },
  82    { SCMP_SYS(ustat),                  QEMU_SECCOMP_SET_OBSOLETE },
  83    /* privileged */
  84    { SCMP_SYS(setuid),                 QEMU_SECCOMP_SET_PRIVILEGED },
  85    { SCMP_SYS(setgid),                 QEMU_SECCOMP_SET_PRIVILEGED },
  86    { SCMP_SYS(setpgid),                QEMU_SECCOMP_SET_PRIVILEGED },
  87    { SCMP_SYS(setsid),                 QEMU_SECCOMP_SET_PRIVILEGED },
  88    { SCMP_SYS(setreuid),               QEMU_SECCOMP_SET_PRIVILEGED },
  89    { SCMP_SYS(setregid),               QEMU_SECCOMP_SET_PRIVILEGED },
  90    { SCMP_SYS(setresuid),              QEMU_SECCOMP_SET_PRIVILEGED },
  91    { SCMP_SYS(setresgid),              QEMU_SECCOMP_SET_PRIVILEGED },
  92    { SCMP_SYS(setfsuid),               QEMU_SECCOMP_SET_PRIVILEGED },
  93    { SCMP_SYS(setfsgid),               QEMU_SECCOMP_SET_PRIVILEGED },
  94    /* spawn */
  95    { SCMP_SYS(fork),                   QEMU_SECCOMP_SET_SPAWN },
  96    { SCMP_SYS(vfork),                  QEMU_SECCOMP_SET_SPAWN },
  97    { SCMP_SYS(execve),                 QEMU_SECCOMP_SET_SPAWN },
  98    /* resource control */
  99    { SCMP_SYS(getpriority),            QEMU_SECCOMP_SET_RESOURCECTL },
 100    { SCMP_SYS(setpriority),            QEMU_SECCOMP_SET_RESOURCECTL },
 101    { SCMP_SYS(sched_setparam),         QEMU_SECCOMP_SET_RESOURCECTL },
 102    { SCMP_SYS(sched_getparam),         QEMU_SECCOMP_SET_RESOURCECTL },
 103    { SCMP_SYS(sched_setscheduler),     QEMU_SECCOMP_SET_RESOURCECTL,
 104      ARRAY_SIZE(sched_setscheduler_arg), sched_setscheduler_arg },
 105    { SCMP_SYS(sched_getscheduler),     QEMU_SECCOMP_SET_RESOURCECTL },
 106    { SCMP_SYS(sched_setaffinity),      QEMU_SECCOMP_SET_RESOURCECTL },
 107    { SCMP_SYS(sched_getaffinity),      QEMU_SECCOMP_SET_RESOURCECTL },
 108    { SCMP_SYS(sched_get_priority_max), QEMU_SECCOMP_SET_RESOURCECTL },
 109    { SCMP_SYS(sched_get_priority_min), QEMU_SECCOMP_SET_RESOURCECTL },
 110};
 111
 112static inline __attribute__((unused)) int
 113qemu_seccomp(unsigned int operation, unsigned int flags, void *args)
 114{
 115#ifdef __NR_seccomp
 116    return syscall(__NR_seccomp, operation, flags, args);
 117#else
 118    errno = ENOSYS;
 119    return -1;
 120#endif
 121}
 122
 123static uint32_t qemu_seccomp_get_kill_action(void)
 124{
 125#if defined(SECCOMP_GET_ACTION_AVAIL) && defined(SCMP_ACT_KILL_PROCESS) && \
 126    defined(SECCOMP_RET_KILL_PROCESS)
 127    {
 128        uint32_t action = SECCOMP_RET_KILL_PROCESS;
 129
 130        if (qemu_seccomp(SECCOMP_GET_ACTION_AVAIL, 0, &action) == 0) {
 131            return SCMP_ACT_KILL_PROCESS;
 132        }
 133    }
 134#endif
 135
 136    return SCMP_ACT_TRAP;
 137}
 138
 139
 140static int seccomp_start(uint32_t seccomp_opts)
 141{
 142    int rc = 0;
 143    unsigned int i = 0;
 144    scmp_filter_ctx ctx;
 145    uint32_t action = qemu_seccomp_get_kill_action();
 146
 147    ctx = seccomp_init(SCMP_ACT_ALLOW);
 148    if (ctx == NULL) {
 149        rc = -1;
 150        goto seccomp_return;
 151    }
 152
 153    rc = seccomp_attr_set(ctx, SCMP_FLTATR_CTL_TSYNC, 1);
 154    if (rc != 0) {
 155        goto seccomp_return;
 156    }
 157
 158    for (i = 0; i < ARRAY_SIZE(blacklist); i++) {
 159        if (!(seccomp_opts & blacklist[i].set)) {
 160            continue;
 161        }
 162
 163        rc = seccomp_rule_add_array(ctx, action, blacklist[i].num,
 164                                    blacklist[i].narg, blacklist[i].arg_cmp);
 165        if (rc < 0) {
 166            goto seccomp_return;
 167        }
 168    }
 169
 170    rc = seccomp_load(ctx);
 171
 172  seccomp_return:
 173    seccomp_release(ctx);
 174    return rc;
 175}
 176
 177#ifdef CONFIG_SECCOMP
 178int parse_sandbox(void *opaque, QemuOpts *opts, Error **errp)
 179{
 180    if (qemu_opt_get_bool(opts, "enable", false)) {
 181        uint32_t seccomp_opts = QEMU_SECCOMP_SET_DEFAULT
 182                | QEMU_SECCOMP_SET_OBSOLETE;
 183        const char *value = NULL;
 184
 185        value = qemu_opt_get(opts, "obsolete");
 186        if (value) {
 187            if (g_str_equal(value, "allow")) {
 188                seccomp_opts &= ~QEMU_SECCOMP_SET_OBSOLETE;
 189            } else if (g_str_equal(value, "deny")) {
 190                /* this is the default option, this if is here
 191                 * to provide a little bit of consistency for
 192                 * the command line */
 193            } else {
 194                error_setg(errp, "invalid argument for obsolete");
 195                return -1;
 196            }
 197        }
 198
 199        value = qemu_opt_get(opts, "elevateprivileges");
 200        if (value) {
 201            if (g_str_equal(value, "deny")) {
 202                seccomp_opts |= QEMU_SECCOMP_SET_PRIVILEGED;
 203            } else if (g_str_equal(value, "children")) {
 204                seccomp_opts |= QEMU_SECCOMP_SET_PRIVILEGED;
 205
 206                /* calling prctl directly because we're
 207                 * not sure if host has CAP_SYS_ADMIN set*/
 208                if (prctl(PR_SET_NO_NEW_PRIVS, 1)) {
 209                    error_setg(errp, "failed to set no_new_privs aborting");
 210                    return -1;
 211                }
 212            } else if (g_str_equal(value, "allow")) {
 213                /* default value */
 214            } else {
 215                error_setg(errp, "invalid argument for elevateprivileges");
 216                return -1;
 217            }
 218        }
 219
 220        value = qemu_opt_get(opts, "spawn");
 221        if (value) {
 222            if (g_str_equal(value, "deny")) {
 223                seccomp_opts |= QEMU_SECCOMP_SET_SPAWN;
 224            } else if (g_str_equal(value, "allow")) {
 225                /* default value */
 226            } else {
 227                error_setg(errp, "invalid argument for spawn");
 228                return -1;
 229            }
 230        }
 231
 232        value = qemu_opt_get(opts, "resourcecontrol");
 233        if (value) {
 234            if (g_str_equal(value, "deny")) {
 235                seccomp_opts |= QEMU_SECCOMP_SET_RESOURCECTL;
 236            } else if (g_str_equal(value, "allow")) {
 237                /* default value */
 238            } else {
 239                error_setg(errp, "invalid argument for resourcecontrol");
 240                return -1;
 241            }
 242        }
 243
 244        if (seccomp_start(seccomp_opts) < 0) {
 245            error_setg(errp, "failed to install seccomp syscall filter "
 246                       "in the kernel");
 247            return -1;
 248        }
 249    }
 250
 251    return 0;
 252}
 253
 254static QemuOptsList qemu_sandbox_opts = {
 255    .name = "sandbox",
 256    .implied_opt_name = "enable",
 257    .head = QTAILQ_HEAD_INITIALIZER(qemu_sandbox_opts.head),
 258    .desc = {
 259        {
 260            .name = "enable",
 261            .type = QEMU_OPT_BOOL,
 262        },
 263        {
 264            .name = "obsolete",
 265            .type = QEMU_OPT_STRING,
 266        },
 267        {
 268            .name = "elevateprivileges",
 269            .type = QEMU_OPT_STRING,
 270        },
 271        {
 272            .name = "spawn",
 273            .type = QEMU_OPT_STRING,
 274        },
 275        {
 276            .name = "resourcecontrol",
 277            .type = QEMU_OPT_STRING,
 278        },
 279        { /* end of list */ }
 280    },
 281};
 282
 283static void seccomp_register(void)
 284{
 285    bool add = false;
 286
 287    /* FIXME: use seccomp_api_get() >= 2 check when released */
 288
 289#if defined(SECCOMP_FILTER_FLAG_TSYNC)
 290    int check;
 291
 292    /* check host TSYNC capability, it returns errno == ENOSYS if unavailable */
 293    check = qemu_seccomp(SECCOMP_SET_MODE_FILTER,
 294                         SECCOMP_FILTER_FLAG_TSYNC, NULL);
 295    if (check < 0 && errno == EFAULT) {
 296        add = true;
 297    }
 298#endif
 299
 300    if (add) {
 301        qemu_add_opts(&qemu_sandbox_opts);
 302    }
 303}
 304opts_init(seccomp_register);
 305#endif
 306