cosmopolitan/libc/mem/pledge.c

/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
│vi: set net ft=c ts=2 sts=2 sw=2 fenc=utf-8                                :vi│
╞══════════════════════════════════════════════════════════════════════════════╡
│ Copyright 2022 Justine Alexandra Roberts Tunney                              │
│                                                                              │
│ Permission to use, copy, modify, and/or distribute this software for         │
│ any purpose with or without fee is hereby granted, provided that the         │
│ above copyright notice and this permission notice appear in all copies.      │
│                                                                              │
│ THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL                │
│ WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED                │
│ WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE             │
│ AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL         │
│ DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR        │
│ PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER               │
│ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR             │
│ PERFORMANCE OF THIS SOFTWARE.                                                │
╚─────────────────────────────────────────────────────────────────────────────*/
#include "libc/assert.h"
#include "libc/calls/calls.h"
#include "libc/calls/strace.internal.h"
#include "libc/calls/struct/bpf.h"
#include "libc/calls/struct/filter.h"
#include "libc/calls/struct/seccomp.h"
#include "libc/calls/syscall-sysv.internal.h"
#include "libc/calls/syscall_support-sysv.internal.h"
#include "libc/dce.h"
#include "libc/intrin/kprintf.h"
#include "libc/intrin/promises.internal.h"
#include "libc/limits.h"
#include "libc/macros.internal.h"
#include "libc/mem/mem.h"
#include "libc/runtime/runtime.h"
#include "libc/sock/struct/sockaddr.h"
#include "libc/str/str.h"
#include "libc/sysv/consts/af.h"
#include "libc/sysv/consts/audit.h"
#include "libc/sysv/consts/f.h"
#include "libc/sysv/consts/map.h"
#include "libc/sysv/consts/nrlinux.h"
#include "libc/sysv/consts/o.h"
#include "libc/sysv/consts/pr.h"
#include "libc/sysv/consts/prot.h"
#include "libc/sysv/errfuns.h"

#define READONLY  0x8000
#define WRITEONLY 0x4000
#define INET      0x8000
#define UNIX      0x4000
#define ADDRLESS  0x2000
#define LOCK      0x8000
#define TTY       0x8000

#define OFF(f)         offsetof(struct seccomp_data, f)
#define PLEDGE(pledge) pledge, ARRAYLEN(pledge)

struct Filter {
  size_t n;
  struct sock_filter *p;
};

static const uint16_t kPledgeLinuxDefault[] = {
    __NR_linux_exit,  //
};

static const uint16_t kPledgeLinuxStdio[] = {
    __NR_linux_exit_group,         //
    __NR_linux_clock_getres,       //
    __NR_linux_clock_gettime,      //
    __NR_linux_clock_nanosleep,    //
    __NR_linux_close,              //
    __NR_linux_write,              //
    __NR_linux_writev,             //
    __NR_linux_pwrite,             //
    __NR_linux_pwritev,            //
    __NR_linux_pwritev2,           //
    __NR_linux_read,               //
    __NR_linux_readv,              //
    __NR_linux_pread,              //
    __NR_linux_preadv,             //
    __NR_linux_preadv2,            //
    __NR_linux_dup,                //
    __NR_linux_dup2,               //
    __NR_linux_dup3,               //
    __NR_linux_fchdir,             //
    __NR_linux_fcntl,              //
    __NR_linux_fstat,              //
    __NR_linux_fsync,              //
    __NR_linux_fdatasync,          //
    __NR_linux_ftruncate,          //
    __NR_linux_getdents,           //
    __NR_linux_getegid,            //
    __NR_linux_getrandom,          //
    __NR_linux_getgroups,          //
    __NR_linux_getpgid,            //
    __NR_linux_getpgrp,            //
    __NR_linux_getpid,             //
    __NR_linux_gettid,             //
    __NR_linux_getuid,             //
    __NR_linux_getgid,             //
    __NR_linux_getsid,             //
    __NR_linux_getppid,            //
    __NR_linux_geteuid,            //
    __NR_linux_getrlimit,          //
    __NR_linux_getresgid,          //
    __NR_linux_getresuid,          //
    __NR_linux_getitimer,          //
    __NR_linux_setitimer,          //
    __NR_linux_gettimeofday,       //
    __NR_linux_copy_file_range,    //
    __NR_linux_splice,             //
    __NR_linux_lseek,              //
    __NR_linux_tee,                //
    __NR_linux_brk,                //
    __NR_linux_mmap,               //
    __NR_linux_msync,              //
    __NR_linux_munmap,             //
    __NR_linux_madvise,            //
    __NR_linux_fadvise,            //
    __NR_linux_mprotect,           //
    __NR_linux_arch_prctl,         //
    __NR_linux_set_tid_address,    //
    __NR_linux_nanosleep,          //
    __NR_linux_pipe,               //
    __NR_linux_pipe2,              //
    __NR_linux_poll,               //
    __NR_linux_select,             //
    __NR_linux_recvfrom,           //
    __NR_linux_sendto | ADDRLESS,  //
    __NR_linux_ioctl,              //
    __NR_linux_shutdown,           //
    __NR_linux_sigaction,          //
    __NR_linux_sigaltstack,        //
    __NR_linux_sigprocmask,        //
    __NR_linux_sigsuspend,         //
    __NR_linux_sigreturn,          //
    __NR_linux_socketpair,         //
    __NR_linux_umask,              //
    __NR_linux_wait4,              //
    __NR_linux_uname,              //
    __NR_linux_prctl,              //
};

static const uint16_t kPledgeLinuxFlock[] = {
    __NR_linux_flock,         //
    __NR_linux_fcntl | LOCK,  //
};

static const uint16_t kPledgeLinuxRpath[] = {
    __NR_linux_chdir,              //
    __NR_linux_getcwd,             //
    __NR_linux_open | READONLY,    //
    __NR_linux_openat | READONLY,  //
    __NR_linux_stat,               //
    __NR_linux_lstat,              //
    __NR_linux_fstat,              //
    __NR_linux_fstatat,            //
    __NR_linux_access,             //
    __NR_linux_faccessat,          //
    __NR_linux_readlink,           //
    __NR_linux_readlinkat,         //
    __NR_linux_statfs,             //
    __NR_linux_fstatfs,            //
};

static const uint16_t kPledgeLinuxWpath[] = {
    __NR_linux_getcwd,              //
    __NR_linux_open | WRITEONLY,    //
    __NR_linux_openat | WRITEONLY,  //
    __NR_linux_stat,                //
    __NR_linux_fstat,               //
    __NR_linux_lstat,               //
    __NR_linux_fstatat,             //
    __NR_linux_access,              //
    __NR_linux_faccessat,           //
    __NR_linux_readlinkat,          //
    __NR_linux_chmod,               //
    __NR_linux_fchmod,              //
    __NR_linux_fchmodat,            //
};

static const uint16_t kPledgeLinuxCpath[] = {
    __NR_linux_open,       //
    __NR_linux_openat,     //
    __NR_linux_rename,     //
    __NR_linux_renameat,   //
    __NR_linux_renameat2,  //
    __NR_linux_link,       //
    __NR_linux_linkat,     //
    __NR_linux_symlink,    //
    __NR_linux_symlinkat,  //
    __NR_linux_rmdir,      //
    __NR_linux_unlink,     //
    __NR_linux_unlinkat,   //
    __NR_linux_mkdir,      //
    __NR_linux_mkdirat,    //
};

static const uint16_t kPledgeLinuxDpath[] = {
    __NR_linux_mknod,    //
    __NR_linux_mknodat,  //
};

static const uint16_t kPledgeLinuxFattr[] = {
    __NR_linux_chmod,      //
    __NR_linux_fchmod,     //
    __NR_linux_fchmodat,   //
    __NR_linux_utime,      //
    __NR_linux_utimes,     //
    __NR_linux_futimesat,  //
    __NR_linux_utimensat,  //
};

static const uint16_t kPledgeLinuxInet[] = {
    __NR_linux_socket | INET,  //
    __NR_linux_listen,         //
    __NR_linux_bind,           //
    __NR_linux_sendto,         //
    __NR_linux_connect,        //
    __NR_linux_accept,         //
    __NR_linux_accept4,        //
    __NR_linux_getsockopt,     //
    __NR_linux_setsockopt,     //
    __NR_linux_getpeername,    //
    __NR_linux_getsockname,    //
};

static const uint16_t kPledgeLinuxUnix[] = {
    __NR_linux_socket | UNIX,  //
    __NR_linux_listen,         //
    __NR_linux_bind,           //
    __NR_linux_connect,        //
    __NR_linux_sendto,         //
    __NR_linux_accept,         //
    __NR_linux_accept4,        //
    __NR_linux_getsockopt,     //
    __NR_linux_setsockopt,     //
    __NR_linux_getpeername,    //
    __NR_linux_getsockname,    //
};

static const uint16_t kPledgeLinuxDns[] = {
    __NR_linux_socket | INET,  //
    __NR_linux_sendto,         //
    __NR_linux_connect,        //
    __NR_linux_recvfrom,       //
};

static const uint16_t kPledgeLinuxTty[] = {
    __NR_linux_ioctl | TTY,  //
};

static const uint16_t kPledgeLinuxRecvfd[] = {
    __NR_linux_recvmsg,  //
};

static const uint16_t kPledgeLinuxProc[] = {
    __NR_linux_fork,         //
    __NR_linux_vfork,        //
    __NR_linux_clone,        //
    __NR_linux_kill,         //
    __NR_linux_setsid,       //
    __NR_linux_setpgid,      //
    __NR_linux_prlimit,      //
    __NR_linux_setrlimit,    //
    __NR_linux_getpriority,  //
    __NR_linux_setpriority,  //
};

static const uint16_t kPledgeLinuxThread[] = {
    __NR_linux_clone,  //
    __NR_linux_futex,  //
};

static const uint16_t kPledgeLinuxId[] = {
    __NR_linux_setuid,       //
    __NR_linux_setreuid,     //
    __NR_linux_setresuid,    //
    __NR_linux_setgid,       //
    __NR_linux_setregid,     //
    __NR_linux_setresgid,    //
    __NR_linux_setgroups,    //
    __NR_linux_prlimit,      //
    __NR_linux_setrlimit,    //
    __NR_linux_getpriority,  //
    __NR_linux_setpriority,  //
    __NR_linux_setfsuid,     //
    __NR_linux_setfsgid,     //
};

static const uint16_t kPledgeLinuxExec[] = {
    __NR_linux_execve,             //
    __NR_linux_execveat,           //
    __NR_linux_access,             //
    __NR_linux_faccessat,          //
    __NR_linux_open | READONLY,    //
    __NR_linux_openat | READONLY,  //
};

static const uint16_t kPledgeLinuxExec2[] = {
    __NR_linux_execve,    //
    __NR_linux_execveat,  //
};

static const struct Pledges {
  const char *name;
  const uint16_t *syscalls;
  const size_t len;
} kPledgeLinux[] = {
    [PROMISE_DEFAULT] = {"default", PLEDGE(kPledgeLinuxDefault)},      //
    [PROMISE_STDIO] = {"stdio", PLEDGE(kPledgeLinuxStdio)},            //
    [PROMISE_RPATH] = {"rpath", PLEDGE(kPledgeLinuxRpath)},            //
    [PROMISE_WPATH] = {"wpath", PLEDGE(kPledgeLinuxWpath)},            //
    [PROMISE_CPATH] = {"cpath", PLEDGE(kPledgeLinuxCpath)},            //
    [PROMISE_DPATH] = {"dpath", PLEDGE(kPledgeLinuxDpath)},            //
    [PROMISE_FLOCK] = {"flock", PLEDGE(kPledgeLinuxFlock)},            //
    [PROMISE_FATTR] = {"fattr", PLEDGE(kPledgeLinuxFattr)},            //
    [PROMISE_INET] = {"inet", PLEDGE(kPledgeLinuxInet)},               //
    [PROMISE_UNIX] = {"unix", PLEDGE(kPledgeLinuxUnix)},               //
    [PROMISE_DNS] = {"dns", PLEDGE(kPledgeLinuxDns)},                  //
    [PROMISE_TTY] = {"tty", PLEDGE(kPledgeLinuxTty)},                  //
    [PROMISE_RECVFD] = {"recvfd", PLEDGE(kPledgeLinuxRecvfd)},         //
    [PROMISE_PROC] = {"proc", PLEDGE(kPledgeLinuxProc)},               //
    [PROMISE_THREAD] = {"thread", PLEDGE(kPledgeLinuxThread)},         //
    [PROMISE_EXEC] = {"exec", PLEDGE(kPledgeLinuxExec)},               //
    [PROMISE_EXECNATIVE] = {"execnative", PLEDGE(kPledgeLinuxExec2)},  //
    [PROMISE_ID] = {"id", PLEDGE(kPledgeLinuxId)},                     //
    [PROMISE_MAX + 1] = {0},                                           //
};

static const struct sock_filter kFilterStart[] = {
    // make sure this isn't an i386 binary or something
    BPF_STMT(BPF_LD | BPF_W | BPF_ABS, OFF(arch)),
    BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, AUDIT_ARCH_X86_64, 1, 0),
    BPF_STMT(BPF_RET | BPF_K, SECCOMP_RET_KILL_PROCESS),
    // each filter assumes ordinal is already loaded into accumulator
    BPF_STMT(BPF_LD | BPF_W | BPF_ABS, OFF(nr)),
};

static const struct sock_filter kFilterEnd[] = {
    // if syscall isn't whitelisted then have it return -EPERM (-1)
    BPF_STMT(BPF_RET | BPF_K, SECCOMP_RET_ERRNO | (1 & SECCOMP_RET_DATA)),
};

static bool AppendFilter(struct Filter *f, struct sock_filter *p, size_t n) {
  size_t m;
  struct sock_filter *q;
  m = f->n + n;
  if (!(q = realloc(f->p, m * sizeof(*f->p)))) return false;
  memcpy(q + f->n, p, n * sizeof(*q));
  f->p = q;
  f->n = m;
  return true;
}

// SYSCALL is only allowed in the .privileged section
// We assume program image is loaded in 32-bit spaces
static bool AppendOriginVerification(struct Filter *f) {
  intptr_t x = (intptr_t)__privileged_start;
  intptr_t y = (intptr_t)__privileged_end;
  assert(0 < x && x < y && y < INT_MAX);
  struct sock_filter fragment[] = {
      /*L0*/ BPF_STMT(BPF_LD | BPF_W | BPF_ABS, OFF(instruction_pointer) + 4),
      /*L1*/ BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, 0, 0, 5 - 2),
      /*L2*/ BPF_STMT(BPF_LD | BPF_W | BPF_ABS, OFF(instruction_pointer)),
      /*L3*/ BPF_JUMP(BPF_JMP | BPF_JGE | BPF_K, x, 0, 5 - 4),
      /*L4*/ BPF_JUMP(BPF_JMP | BPF_JGE | BPF_K, y, 0, 6 - 5),
      /*L5*/ BPF_STMT(BPF_RET | BPF_K, SECCOMP_RET_KILL),
      /*L6*/ BPF_STMT(BPF_LD | BPF_W | BPF_ABS, OFF(nr)),
      /*L7*/ /* next filter */
  };
  return AppendFilter(f, PLEDGE(fragment));
}

// Authorize specific system call w/o considering its arguments.
static bool AllowSyscall(struct Filter *f, uint16_t w) {
  struct sock_filter fragment[] = {
      /*L0*/ BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, w, 0, 2 - 1),
      /*L1*/ BPF_STMT(BPF_RET | BPF_K, SECCOMP_RET_ALLOW),
      /*L2*/ /* next filter */
  };
  return AppendFilter(f, PLEDGE(fragment));
}

// The second argument of ioctl() must be one of:
//
//   - FIONREAD (0x541b)
//   - FIONBIO  (0x5421)
//   - FIOCLEX  (0x5451)
//   - FIONCLEX (0x5450)
//
static bool AllowIoctl(struct Filter *f) {
  static const struct sock_filter fragment[] = {
      /*L0*/ BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, __NR_linux_ioctl, 0, 8 - 1),
      /*L1*/ BPF_STMT(BPF_LD | BPF_W | BPF_ABS, OFF(args[1])),
      /*L2*/ BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, 0x541b, 6 - 3, 0),
      /*L3*/ BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, 0x5421, 6 - 4, 0),
      /*L4*/ BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, 0x5451, 6 - 5, 0),
      /*L5*/ BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, 0x5450, 0, 7 - 6),
      /*L6*/ BPF_STMT(BPF_RET | BPF_K, SECCOMP_RET_ALLOW),
      /*L7*/ BPF_STMT(BPF_LD | BPF_W | BPF_ABS, OFF(nr)),
      /*L8*/ /* next filter */
  };
  return AppendFilter(f, PLEDGE(fragment));
}

// The second argument of ioctl() must be one of:
//
//   - TCGETS     (0x5401)
//   - TCSETS     (0x5402)
//   - TCSETSW    (0x5403)
//   - TCSETSF    (0x5404)
//   - TIOCGWINSZ (0x5413)
//   - TIOCSPGRP  (0x5410)
//   - TIOCGPGRP  (0x540f)
//   - TIOCSWINSZ (0x5414)
//   - TIOCSBRK   (0x5427)
//   - TCFLSH     (0x540b)
//
static bool AllowIoctlTty(struct Filter *f) {
  static const struct sock_filter fragment[] = {
      /* L0*/ BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, __NR_linux_ioctl, 0, 14 - 1),
      /* L1*/ BPF_STMT(BPF_LD | BPF_W | BPF_ABS, OFF(args[1])),
      /* L2*/ BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, 0x5401, 12 - 3, 0),
      /* L3*/ BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, 0x5402, 12 - 4, 0),
      /* L4*/ BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, 0x5403, 12 - 5, 0),
      /* L5*/ BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, 0x5404, 12 - 6, 0),
      /* L6*/ BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, 0x5413, 12 - 7, 0),
      /* L7*/ BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, 0x5410, 12 - 8, 0),
      /* L8*/ BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, 0x540f, 12 - 9, 0),
      /* L9*/ BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, 0x5414, 12 - 10, 0),
      /*L10*/ BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, 0x540b, 12 - 11, 0),
      /*L11*/ BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, 0x5427, 0, 13 - 12),
      /*L12*/ BPF_STMT(BPF_RET | BPF_K, SECCOMP_RET_ALLOW),
      /*L13*/ BPF_STMT(BPF_LD | BPF_W | BPF_ABS, OFF(nr)),
      /*L14*/ /* next filter */
  };
  return AppendFilter(f, PLEDGE(fragment));
}

// The level argument of setsockopt() must be one of:
//
//   - SOL_IP     (0)
//   - SOL_SOCKET (1)
//   - SOL_TCP    (6)
//
// The optname argument of setsockopt() must be one of:
//
//   - SO_TYPE      ( 3)
//   - SO_REUSEPORT (15)
//   - SO_REUSEADDR ( 2)
//   - SO_KEEPALIVE ( 9)
//   - SO_RCVTIMEO  (20)
//   - SO_SNDTIMEO  (21)
//   - IP_RECVTTL   (12)
//
static bool AllowSetsockopt(struct Filter *f) {
  static const int nr = __NR_linux_setsockopt;
  static const struct sock_filter fragment[] = {
      /* L0*/ BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, nr, 0, 15 - 1),
      /* L1*/ BPF_STMT(BPF_LD | BPF_W | BPF_ABS, OFF(args[1])),
      /* L2*/ BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, 0, 5 - 3, 0),
      /* L3*/ BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, 1, 5 - 4, 0),
      /* L4*/ BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, 6, 0, 14 - 5),
      /* L5*/ BPF_STMT(BPF_LD | BPF_W | BPF_ABS, OFF(args[2])),
      /* L6*/ BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, 3, 13 - 7, 0),
      /* L7*/ BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, 12, 13 - 8, 0),
      /* L8*/ BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, 15, 13 - 9, 0),
      /* L9*/ BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, 2, 13 - 10, 0),
      /*L10*/ BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, 9, 13 - 11, 0),
      /*L11*/ BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, 20, 13 - 12, 0),
      /*L12*/ BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, 21, 0, 14 - 13),
      /*L13*/ BPF_STMT(BPF_RET | BPF_K, SECCOMP_RET_ALLOW),
      /*L14*/ BPF_STMT(BPF_LD | BPF_W | BPF_ABS, OFF(nr)),
      /*L15*/ /* next filter */
  };
  return AppendFilter(f, PLEDGE(fragment));
}

// The level argument of getsockopt() must be one of:
//
//   - SOL_SOCKET (1)
//   - SOL_TCP    (6)
//
// The optname argument of getsockopt() must be one of:
//
//   - SO_TYPE      ( 3)
//   - SO_REUSEPORT (15)
//   - SO_REUSEADDR ( 2)
//   - SO_KEEPALIVE ( 9)
//   - SO_RCVTIMEO  (20)
//   - SO_SNDTIMEO  (21)
//
static bool AllowGetsockopt(struct Filter *f) {
  static const int nr = __NR_linux_getsockopt;
  static const struct sock_filter fragment[] = {
      /* L0*/ BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, nr, 0, 13 - 1),
      /* L1*/ BPF_STMT(BPF_LD | BPF_W | BPF_ABS, OFF(args[1])),
      /* L2*/ BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, 1, 11 - 3, 0),
      /* L3*/ BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, 6, 11 - 4, 0),
      /* L4*/ BPF_STMT(BPF_LD | BPF_W | BPF_ABS, OFF(args[2])),
      /* L5*/ BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, 3, 11 - 6, 0),
      /* L6*/ BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, 15, 11 - 7, 0),
      /* L7*/ BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, 2, 11 - 8, 0),
      /* L8*/ BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, 9, 11 - 9, 0),
      /* L9*/ BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, 20, 11 - 10, 0),
      /*L10*/ BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, 21, 0, 12 - 11),
      /*L11*/ BPF_STMT(BPF_RET | BPF_K, SECCOMP_RET_ALLOW),
      /*L12*/ BPF_STMT(BPF_LD | BPF_W | BPF_ABS, OFF(nr)),
      /*L13*/ /* next filter */
  };
  return AppendFilter(f, PLEDGE(fragment));
}

// The flags parameter of mmap() must not have:
//
//   - MAP_LOCKED   (0x02000)
//   - MAP_NONBLOCK (0x10000)
//   - MAP_HUGETLB  (0x40000)
//
static bool AllowMmap(struct Filter *f) {
  intptr_t y = (intptr_t)__privileged_end;
  assert(0 < y && y < INT_MAX);
  struct sock_filter fragment[] = {
      /*L0*/ BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, __NR_linux_mmap, 0, 6 - 1),
      /*L1*/ BPF_STMT(BPF_LD | BPF_W | BPF_ABS, OFF(args[3])),  // flags
      /*L2*/ BPF_STMT(BPF_ALU | BPF_AND | BPF_K, 0x52000),
      /*L3*/ BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, 0, 0, 5 - 4),
      /*L4*/ BPF_STMT(BPF_RET | BPF_K, SECCOMP_RET_ALLOW),
      /*L5*/ BPF_STMT(BPF_LD | BPF_W | BPF_ABS, OFF(nr)),
      /*L6*/ /* next filter */
  };
  return AppendFilter(f, PLEDGE(fragment));
}

// The prot parameter of mmap() may only have:
//
//   - PROT_NONE  (0)
//   - PROT_READ  (1)
//   - PROT_WRITE (2)
//
// The flags parameter must not have:
//
//   - MAP_LOCKED   (0x02000)
//   - MAP_POPULATE (0x08000)
//   - MAP_NONBLOCK (0x10000)
//   - MAP_HUGETLB  (0x40000)
//
static bool AllowMmapNoexec(struct Filter *f) {
  static const struct sock_filter fragment[] = {
      /*L0*/ BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, __NR_linux_mmap, 0, 9 - 1),
      /*L1*/ BPF_STMT(BPF_LD | BPF_W | BPF_ABS, OFF(args[2])),  // prot
      /*L2*/ BPF_STMT(BPF_ALU | BPF_AND | BPF_K, ~(PROT_READ | PROT_WRITE)),
      /*L3*/ BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, 0, 0, 8 - 4),
      /*L4*/ BPF_STMT(BPF_LD | BPF_W | BPF_ABS, OFF(args[3])),  // flags
      /*L5*/ BPF_STMT(BPF_ALU | BPF_AND | BPF_K, 0x5a000),
      /*L6*/ BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, 0, 0, 8 - 7),
      /*L7*/ BPF_STMT(BPF_RET | BPF_K, SECCOMP_RET_ALLOW),
      /*L8*/ BPF_STMT(BPF_LD | BPF_W | BPF_ABS, OFF(nr)),
      /*L9*/ /* next filter */
  };
  return AppendFilter(f, PLEDGE(fragment));
}

// The prot parameter of mprotect() may only have:
//
//   - PROT_NONE  (0)
//   - PROT_READ  (1)
//   - PROT_WRITE (2)
//
static bool AllowMprotectNoexec(struct Filter *f) {
  static const struct sock_filter fragment[] = {
      /*L0*/ BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, __NR_linux_mprotect, 0, 6 - 1),
      /*L1*/ BPF_STMT(BPF_LD | BPF_W | BPF_ABS, OFF(args[2])),  // prot
      /*L2*/ BPF_STMT(BPF_ALU | BPF_AND | BPF_K, ~(PROT_READ | PROT_WRITE)),
      /*L3*/ BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, 0, 0, 5 - 4),
      /*L4*/ BPF_STMT(BPF_RET | BPF_K, SECCOMP_RET_ALLOW),
      /*L5*/ BPF_STMT(BPF_LD | BPF_W | BPF_ABS, OFF(nr)),
      /*L6*/ /* next filter */
  };
  return AppendFilter(f, PLEDGE(fragment));
}

// The open() system call is permitted only when
//
//   - (flags & O_ACCMODE) == O_RDONLY
//
static bool AllowOpenReadonly(struct Filter *f) {
  static const struct sock_filter fragment[] = {
      /*L0*/ BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, __NR_linux_open, 0, 6 - 1),
      /*L1*/ BPF_STMT(BPF_LD | BPF_W | BPF_ABS, OFF(args[1])),
      /*L2*/ BPF_STMT(BPF_ALU | BPF_AND | BPF_K, O_ACCMODE),
      /*L3*/ BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, O_RDONLY, 0, 5 - 4),
      /*L4*/ BPF_STMT(BPF_RET | BPF_K, SECCOMP_RET_ALLOW),
      /*L5*/ BPF_STMT(BPF_LD | BPF_W | BPF_ABS, OFF(nr)),
      /*L6*/ /* next filter */
  };
  return AppendFilter(f, PLEDGE(fragment));
}

// The flags parameter of open() must not have:
//
//   - O_WRONLY (1)
//   - O_RDWR   (2)
//
static bool AllowOpenatReadonly(struct Filter *f) {
  static const struct sock_filter fragment[] = {
      /*L0*/ BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, __NR_linux_openat, 0, 6 - 1),
      /*L1*/ BPF_STMT(BPF_LD | BPF_W | BPF_ABS, OFF(args[2])),
      /*L2*/ BPF_STMT(BPF_ALU | BPF_AND | BPF_K, O_ACCMODE),
      /*L3*/ BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, O_RDONLY, 0, 5 - 4),
      /*L4*/ BPF_STMT(BPF_RET | BPF_K, SECCOMP_RET_ALLOW),
      /*L5*/ BPF_STMT(BPF_LD | BPF_W | BPF_ABS, OFF(nr)),
      /*L6*/ /* next filter */
  };
  return AppendFilter(f, PLEDGE(fragment));
}

// The open() flags parameter must not contain
//
//   - O_CREAT   (000000100)
//   - O_TMPFILE (020200000)
//
static bool AllowOpenWriteonly(struct Filter *f) {
  static const struct sock_filter fragment[] = {
      /*L0*/ BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, __NR_linux_open, 0, 6 - 1),
      /*L1*/ BPF_STMT(BPF_LD | BPF_W | BPF_ABS, OFF(args[1])),
      /*L2*/ BPF_STMT(BPF_ALU | BPF_AND | BPF_K, 020200100),
      /*L3*/ BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, 0, 0, 5 - 4),
      /*L4*/ BPF_STMT(BPF_RET | BPF_K, SECCOMP_RET_ALLOW),
      /*L5*/ BPF_STMT(BPF_LD | BPF_W | BPF_ABS, OFF(nr)),
      /*L6*/ /* next filter */
  };
  return AppendFilter(f, PLEDGE(fragment));
}

// The openat() flags parameter must not contain
//
//   - O_CREAT   (000000100)
//   - O_TMPFILE (020200000)
//
static bool AllowOpenatWriteonly(struct Filter *f) {
  static const struct sock_filter fragment[] = {
      /*L0*/ BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, __NR_linux_openat, 0, 6 - 1),
      /*L1*/ BPF_STMT(BPF_LD | BPF_W | BPF_ABS, OFF(args[2])),
      /*L2*/ BPF_STMT(BPF_ALU | BPF_AND | BPF_K, 020200100),
      /*L3*/ BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, 0, 0, 5 - 4),
      /*L4*/ BPF_STMT(BPF_RET | BPF_K, SECCOMP_RET_ALLOW),
      /*L5*/ BPF_STMT(BPF_LD | BPF_W | BPF_ABS, OFF(nr)),
      /*L6*/ /* next filter */
  };
  return AppendFilter(f, PLEDGE(fragment));
}

// If the flags parameter of open() has one of:
//
//   - O_CREAT   (000000100)
//   - O_TMPFILE (020200000)
//
// Then the mode parameter must not have:
//
//   - S_ISVTX (01000 sticky)
//   - S_ISGID (02000 setgid)
//   - S_ISUID (04000 setuid)
//
static bool AllowOpen(struct Filter *f) {
  static const struct sock_filter fragment[] = {
      /* L0*/ BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, __NR_linux_open, 0, 12 - 1),
      /* L1*/ BPF_STMT(BPF_LD | BPF_W | BPF_ABS, OFF(args[1])),
      /* L2*/ BPF_STMT(BPF_ALU | BPF_AND | BPF_K, 000000100),
      /* L3*/ BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, 000000100, 7 - 4, 0),
      /* L4*/ BPF_STMT(BPF_LD | BPF_W | BPF_ABS, OFF(args[1])),
      /* L5*/ BPF_STMT(BPF_ALU | BPF_AND | BPF_K, 020200000),
      /* L6*/ BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, 020200000, 0, 10 - 7),
      /* L7*/ BPF_STMT(BPF_LD | BPF_W | BPF_ABS, OFF(args[2])),
      /* L8*/ BPF_STMT(BPF_ALU | BPF_AND | BPF_K, 07000),
      /* L9*/ BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, 0, 0, 11 - 10),
      /*L10*/ BPF_STMT(BPF_RET | BPF_K, SECCOMP_RET_ALLOW),
      /*L11*/ BPF_STMT(BPF_LD | BPF_W | BPF_ABS, OFF(nr)),
      /*L12*/ /* next filter */
  };
  return AppendFilter(f, PLEDGE(fragment));
}

// If the flags parameter of openat() has one of:
//
//   - O_CREAT   (000000100)
//   - O_TMPFILE (020200000)
//
// Then the mode parameter must not have:
//
//   - S_ISVTX (01000 sticky)
//   - S_ISGID (02000 setgid)
//   - S_ISUID (04000 setuid)
//
static bool AllowOpenat(struct Filter *f) {
  static const struct sock_filter fragment[] = {
      /* L0*/ BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, __NR_linux_openat, 0, 12 - 1),
      /* L1*/ BPF_STMT(BPF_LD | BPF_W | BPF_ABS, OFF(args[2])),
      /* L2*/ BPF_STMT(BPF_ALU | BPF_AND | BPF_K, 000000100),
      /* L3*/ BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, 000000100, 7 - 4, 0),
      /* L4*/ BPF_STMT(BPF_LD | BPF_W | BPF_ABS, OFF(args[2])),
      /* L5*/ BPF_STMT(BPF_ALU | BPF_AND | BPF_K, 020200000),
      /* L6*/ BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, 020200000, 0, 10 - 7),
      /* L7*/ BPF_STMT(BPF_LD | BPF_W | BPF_ABS, OFF(args[3])),
      /* L8*/ BPF_STMT(BPF_ALU | BPF_AND | BPF_K, 07000),
      /* L9*/ BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, 0, 0, 11 - 10),
      /*L10*/ BPF_STMT(BPF_RET | BPF_K, SECCOMP_RET_ALLOW),
      /*L11*/ BPF_STMT(BPF_LD | BPF_W | BPF_ABS, OFF(nr)),
      /*L12*/ /* next filter */
  };
  return AppendFilter(f, PLEDGE(fragment));
}

// The second argument of fcntl() must be one of:
//
//   - F_DUPFD (0)
//   - F_DUPFD_CLOEXEC (1030)
//   - F_GETFD (1)
//   - F_SETFD (2)
//   - F_GETFL (3)
//   - F_SETFL (4)
//
static bool AllowFcntl(struct Filter *f) {
  static const struct sock_filter fragment[] = {
      /*L0*/ BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, __NR_linux_fcntl, 0, 6 - 1),
      /*L1*/ BPF_STMT(BPF_LD | BPF_W | BPF_ABS, OFF(args[1])),
      /*L2*/ BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, 1030, 4 - 3, 0),
      /*L3*/ BPF_JUMP(BPF_JMP | BPF_JGE | BPF_K, 5, 5 - 4, 0),
      /*L4*/ BPF_STMT(BPF_RET | BPF_K, SECCOMP_RET_ALLOW),
      /*L5*/ BPF_STMT(BPF_LD | BPF_W | BPF_ABS, OFF(nr)),
      /*L6*/ /* next filter */
  };
  return AppendFilter(f, PLEDGE(fragment));
}

// The second argument of fcntl() must be one of:
//
//   - F_GETLK (5)
//   - F_SETLK (6)
//   - F_SETLKW (7)
//
static bool AllowFcntlLock(struct Filter *f) {
  static const struct sock_filter fragment[] = {
      /*L0*/ BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, __NR_linux_fcntl, 0, 6 - 1),
      /*L1*/ BPF_STMT(BPF_LD | BPF_W | BPF_ABS, OFF(args[1])),
      /*L2*/ BPF_JUMP(BPF_JMP | BPF_JGE | BPF_K, 5, 0, 5 - 3),
      /*L3*/ BPF_JUMP(BPF_JMP | BPF_JGE | BPF_K, 8, 5 - 4, 0),
      /*L4*/ BPF_STMT(BPF_RET | BPF_K, SECCOMP_RET_ALLOW),
      /*L5*/ BPF_STMT(BPF_LD | BPF_W | BPF_ABS, OFF(nr)),
      /*L6*/ /* next filter */
  };
  return AppendFilter(f, PLEDGE(fragment));
}

// The addr parameter of sendto() must be
//
//   - NULL
//
static bool AllowSendtoAddrless(struct Filter *f) {
  static const struct sock_filter fragment[] = {
      /*L0*/ BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, __NR_linux_sendto, 0, 7 - 1),
      /*L1*/ BPF_STMT(BPF_LD | BPF_W | BPF_ABS, OFF(args[4]) + 0),
      /*L2*/ BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, 0, 0, 6 - 3),
      /*L3*/ BPF_STMT(BPF_LD | BPF_W | BPF_ABS, OFF(args[4]) + 4),
      /*L4*/ BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, 0, 0, 6 - 3),
      /*L5*/ BPF_STMT(BPF_RET | BPF_K, SECCOMP_RET_ALLOW),
      /*L6*/ BPF_STMT(BPF_LD | BPF_W | BPF_ABS, OFF(nr)),
      /*L7*/ /* next filter */
  };
  return AppendFilter(f, PLEDGE(fragment));
}

// The sig parameter of sigaction() must NOT be
//
//   - SIGSYS (31)
//
static bool AllowSigaction(struct Filter *f) {
  static const int nr = __NR_linux_sigaction;
  static const struct sock_filter fragment[] = {
      /*L0*/ BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, nr, 0, 5 - 1),
      /*L1*/ BPF_STMT(BPF_LD | BPF_W | BPF_ABS, OFF(args[0])),
      /*L2*/ BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, 31, 4 - 3, 0),
      /*L3*/ BPF_STMT(BPF_RET | BPF_K, SECCOMP_RET_ALLOW),
      /*L4*/ BPF_STMT(BPF_LD | BPF_W | BPF_ABS, OFF(nr)),
      /*L5*/ /* next filter */
  };
  return AppendFilter(f, PLEDGE(fragment));
}

// The family parameter of socket() must be one of:
//
//   - AF_INET  (2)
//   - AF_INET6 (10)
//
// The type parameter of socket() will ignore:
//
//   - SOCK_CLOEXEC  (0x80000)
//   - SOCK_NONBLOCK (0x00800)
//
// The type parameter of socket() must be one of:
//
//   - SOCK_STREAM (1)
//   - SOCK_DGRAM  (2)
//
// The protocol parameter of socket() must be one of:
//
//   - 0
//   - IPPROTO_ICMP (1)
//   - IPPROTO_TCP (6)
//   - IPPROTO_UDP (17)
//
static bool AllowSocketInet(struct Filter *f) {
  static const struct sock_filter fragment[] = {
      /* L0*/ BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, __NR_linux_socket, 0, 15 - 1),
      /* L1*/ BPF_STMT(BPF_LD | BPF_W | BPF_ABS, OFF(args[0])),
      /* L2*/ BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, 2, 4 - 3, 0),
      /* L3*/ BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, 10, 0, 14 - 4),
      /* L4*/ BPF_STMT(BPF_LD | BPF_W | BPF_ABS, OFF(args[1])),
      /* L5*/ BPF_STMT(BPF_ALU | BPF_AND | BPF_K, ~0x80800),
      /* L6*/ BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, 1, 8 - 7, 0),
      /* L7*/ BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, 2, 0, 14 - 8),
      /* L8*/ BPF_STMT(BPF_LD | BPF_W | BPF_ABS, OFF(args[2])),
      /* L9*/ BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, 0, 13 - 10, 0),
      /*L10*/ BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, 1, 13 - 11, 0),
      /*L11*/ BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, 6, 13 - 12, 0),
      /*L12*/ BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, 17, 0, 14 - 12),
      /*L13*/ BPF_STMT(BPF_RET | BPF_K, SECCOMP_RET_ALLOW),
      /*L14*/ BPF_STMT(BPF_LD | BPF_W | BPF_ABS, OFF(nr)),
      /*L15*/ /* next filter */
  };
  return AppendFilter(f, PLEDGE(fragment));
}

// The family parameter of socket() must be one of:
//
//   - AF_UNIX (1)
//   - AF_LOCAL (1)
//
// The type parameter of socket() will ignore:
//
//   - SOCK_CLOEXEC  (0x80000)
//   - SOCK_NONBLOCK (0x00800)
//
// The type parameter of socket() must be one of:
//
//   - SOCK_STREAM (1)
//   - SOCK_DGRAM  (2)
//
// The protocol parameter of socket() must be one of:
//
//   - 0
//
static bool AllowSocketUnix(struct Filter *f) {
  static const struct sock_filter fragment[] = {
      /* L0*/ BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, __NR_linux_socket, 0, 11 - 1),
      /* L1*/ BPF_STMT(BPF_LD | BPF_W | BPF_ABS, OFF(args[0])),
      /* L2*/ BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, 1, 0, 10 - 3),
      /* L3*/ BPF_STMT(BPF_LD | BPF_W | BPF_ABS, OFF(args[1])),
      /* L5*/ BPF_STMT(BPF_ALU | BPF_AND | BPF_K, ~0x80800),
      /* L5*/ BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, 1, 7 - 6, 0),
      /* L6*/ BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, 2, 0, 10 - 7),
      /* L7*/ BPF_STMT(BPF_LD | BPF_W | BPF_ABS, OFF(args[2])),
      /* L8*/ BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, 0, 0, 10 - 9),
      /* L9*/ BPF_STMT(BPF_RET | BPF_K, SECCOMP_RET_ALLOW),
      /*L10*/ BPF_STMT(BPF_LD | BPF_W | BPF_ABS, OFF(nr)),
      /*L11*/ /* next filter */
  };
  return AppendFilter(f, PLEDGE(fragment));
}

// The first parameter of prctl() can be any of
//
//   - PR_SET_NAME         (15)
//   - PR_GET_NAME         (16)
//   - PR_GET_SECCOMP      (21)
//   - PR_SET_SECCOMP      (22)
//   - PR_SET_NO_NEW_PRIVS (38)
//
static bool AllowPrctl(struct Filter *f) {
  static const struct sock_filter fragment[] = {
      /*L0*/ BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, __NR_linux_prctl, 0, 9 - 1),
      /*L1*/ BPF_STMT(BPF_LD | BPF_W | BPF_ABS, OFF(args[0])),
      /*L2*/ BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, 15, 7 - 3, 0),
      /*L3*/ BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, 16, 7 - 4, 0),
      /*L4*/ BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, 21, 7 - 5, 0),
      /*L5*/ BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, 22, 7 - 6, 0),
      /*L6*/ BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, 38, 0, 8 - 7),
      /*L7*/ BPF_STMT(BPF_RET | BPF_K, SECCOMP_RET_ALLOW),
      /*L8*/ BPF_STMT(BPF_LD | BPF_W | BPF_ABS, OFF(nr)),
      /*L9*/ /* next filter */
  };
  return AppendFilter(f, PLEDGE(fragment));
}

// The mode parameter of chmod() can't have the following:
//
//   - S_ISVTX (01000 sticky)
//   - S_ISGID (02000 setgid)
//   - S_ISUID (04000 setuid)
//
static bool AllowChmod(struct Filter *f) {
  static const struct sock_filter fragment[] = {
      /*L0*/ BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, __NR_linux_chmod, 0, 6 - 1),
      /*L1*/ BPF_STMT(BPF_LD | BPF_W | BPF_ABS, OFF(args[1])),
      /*L2*/ BPF_STMT(BPF_ALU | BPF_AND | BPF_K, 07000),
      /*L3*/ BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, 0, 0, 5 - 4),
      /*L4*/ BPF_STMT(BPF_RET | BPF_K, SECCOMP_RET_ALLOW),
      /*L5*/ BPF_STMT(BPF_LD | BPF_W | BPF_ABS, OFF(nr)),
      /*L6*/ /* next filter */
  };
  return AppendFilter(f, PLEDGE(fragment));
}

// The mode parameter of fchmod() can't have the following:
//
//   - S_ISVTX (01000 sticky)
//   - S_ISGID (02000 setgid)
//   - S_ISUID (04000 setuid)
//
static bool AllowFchmod(struct Filter *f) {
  static const struct sock_filter fragment[] = {
      /*L0*/ BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, __NR_linux_fchmod, 0, 6 - 1),
      /*L1*/ BPF_STMT(BPF_LD | BPF_W | BPF_ABS, OFF(args[1])),
      /*L2*/ BPF_STMT(BPF_ALU | BPF_AND | BPF_K, 07000),
      /*L3*/ BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, 0, 0, 5 - 4),
      /*L4*/ BPF_STMT(BPF_RET | BPF_K, SECCOMP_RET_ALLOW),
      /*L5*/ BPF_STMT(BPF_LD | BPF_W | BPF_ABS, OFF(nr)),
      /*L6*/ /* next filter */
  };
  return AppendFilter(f, PLEDGE(fragment));
}

// The mode parameter of fchmodat() can't have the following:
//
//   - S_ISVTX (01000 sticky)
//   - S_ISGID (02000 setgid)
//   - S_ISUID (04000 setuid)
//
static bool AllowFchmodat(struct Filter *f) {
  static const struct sock_filter fragment[] = {
      /*L0*/ BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, __NR_linux_fchmodat, 0, 6 - 1),
      /*L1*/ BPF_STMT(BPF_LD | BPF_W | BPF_ABS, OFF(args[2])),
      /*L2*/ BPF_STMT(BPF_ALU | BPF_AND | BPF_K, 07000),
      /*L3*/ BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, 0, 0, 5 - 4),
      /*L4*/ BPF_STMT(BPF_RET | BPF_K, SECCOMP_RET_ALLOW),
      /*L5*/ BPF_STMT(BPF_LD | BPF_W | BPF_ABS, OFF(nr)),
      /*L6*/ /* next filter */
  };
  return AppendFilter(f, PLEDGE(fragment));
}

static bool AppendPledge(struct Filter *f, const uint16_t *p, size_t len, bool needmapexec,
                         bool needmorphing) {
  int i;
  for (i = 0; i < len; ++i) {
    switch (p[i]) {
      case __NR_linux_mmap:
        if (needmapexec) {
          if (!AllowMmap(f)) return false;
        } else {
          if (!AllowMmapNoexec(f)) return false;
        }
        break;
      case __NR_linux_mprotect:
        if (needmorphing) {
          if (!AllowSyscall(f, __NR_linux_mprotect)) return false;
        } else {
          if (!AllowMprotectNoexec(f)) return false;
        }
        break;
      case __NR_linux_chmod:
        if (!AllowChmod(f)) return false;
        break;
      case __NR_linux_fchmod:
        if (!AllowFchmod(f)) return false;
        break;
      case __NR_linux_fchmodat:
        if (!AllowFchmodat(f)) return false;
        break;
      case __NR_linux_sigaction:
        if (!AllowSigaction(f)) return false;
        break;
      case __NR_linux_prctl:
        if (!AllowPrctl(f)) return false;
        break;
      case __NR_linux_open:
        if (!AllowOpen(f)) return false;
        break;
      case __NR_linux_openat:
        if (!AllowOpenat(f)) return false;
        break;
      case __NR_linux_open | READONLY:
        if (!AllowOpenReadonly(f)) return false;
        break;
      case __NR_linux_openat | READONLY:
        if (!AllowOpenatReadonly(f)) return false;
        break;
      case __NR_linux_open | WRITEONLY:
        if (!AllowOpenWriteonly(f)) return false;
        break;
      case __NR_linux_openat | WRITEONLY:
        if (!AllowOpenatWriteonly(f)) return false;
        break;
      case __NR_linux_setsockopt:
        if (!AllowSetsockopt(f)) return false;
        break;
      case __NR_linux_getsockopt:
        if (!AllowGetsockopt(f)) return false;
        break;
      case __NR_linux_fcntl:
        if (!AllowFcntl(f)) return false;
        break;
      case __NR_linux_fcntl | LOCK:
        if (!AllowFcntlLock(f)) return false;
        break;
      case __NR_linux_ioctl:
        if (!AllowIoctl(f)) return false;
        break;
      case __NR_linux_ioctl | TTY:
        if (!AllowIoctlTty(f)) return false;
        break;
      case __NR_linux_socket | INET:
        if (!AllowSocketInet(f)) return false;
        break;
      case __NR_linux_socket | UNIX:
        if (!AllowSocketUnix(f)) return false;
        break;
      case __NR_linux_sendto | ADDRLESS:
        if (!AllowSendtoAddrless(f)) return false;
        break;
      default:
        assert(~p[i] & ~0xfff);
        if (!AllowSyscall(f, p[i])) return false;
        break;
    }
  }
  return true;
}

static int FindPromise(const struct Pledges *p, const char *name, size_t *len) {
  int i;
  for (i = 0; p[i].name; ++i) {
    if (!strcasecmp(name, p[i].name)) {
      *len = p[i].len;
      return i;
    }
  }
  return -1;
}

static int sys_pledge_linux(const char *promises, const char *execpromises) {
  bool ok;
  int rc = -1;
  size_t plen;
  int promise;
  bool needmapexec;
  bool needexecnative;
  bool needmorphing;
  struct Filter f = {0};
  const uint16_t *pledge;
  unsigned long ipromises = -1;
  char *s, *tok, *state, *start;
  if (execpromises) return einval();
  needmapexec = strstr(promises, "exec");
  needmorphing = strstr(promises, "thread");
  needexecnative = strstr(promises, "execnative");
  if ((start = s = strdup(promises)) && AppendFilter(&f, kFilterStart, ARRAYLEN(kFilterStart)) &&
      (needmapexec || needexecnative || AppendOriginVerification(&f)) &&
      AppendPledge(&f, kPledgeLinuxDefault, ARRAYLEN(kPledgeLinuxDefault), needmapexec,
                   needmorphing)) {
    for (ok = true; (tok = strtok_r(start, " \t\r\n", &state)); start = 0) {
      if ((promise = FindPromise(kPledgeLinux, tok, &plen)) != -1) {
        pledge = kPledgeLinux[promise].syscalls;
        ipromises &= ~(1ULL << promise);
      } else {
        ok = false;
        rc = einval();
        break;
      }
      if (!AppendPledge(&f, pledge, plen, needmapexec, needmorphing)) {
        ok = false;
        break;
      }
    }
    if (ok && AppendFilter(&f, kFilterEnd, ARRAYLEN(kFilterEnd)) &&
        (rc = prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0)) != -1) {
      struct sock_fprog sandbox = {.len = f.n, .filter = f.p};
      rc = prctl(PR_SET_SECCOMP, SECCOMP_MODE_FILTER, &sandbox);
    }
    if (!rc) {
      __promises = ipromises;
    }
  }
  free(f.p);
  free(s);
  return rc;
}

static void SetPromises(const char *promises) {
  int promise;
  size_t plen;
  char *tok, *state, *start;
  unsigned long ipromises = -1;
  while ((tok = strtok_r(start, " \t\r\n", &state))) {
    if ((promise = FindPromise(kPledgeLinux, tok, &plen)) != -1) {
      ipromises &= ~(1ULL << promise);
    }
    start = 0;
  }
  __promises = ipromises;
}

/**
 * Restricts system operations, e.g.
 *
 *     pledge("stdio tty", 0);
 *
 * Pledging causes most system calls to become unavailable. Your system
 * call policy is enforced by the kernel, which means it can propagate
 * across execve() if permitted. This system call is supported on
 * OpenBSD and Linux where it's polyfilled using SECCOMP BPF. The way it
 * works on Linux is verboten system calls will raise EPERM whereas
 * OpenBSD just kills the process while logging a helpful message to
 * /var/log/messages explaining which promise category you needed.
 *
 * By default exit() is allowed. This is useful for processes that
 * perform pure computation and interface with the parent via shared
 * memory. On Linux we mean sys_exit (_Exit1), not sys_exit_group
 * (_Exit). The difference is effectively meaningless, since _Exit()
 * will attempt both. All it means is that, if you're using threads,
 * then a `pledge("", 0)` thread can't kill all your threads unless you
 * `pledge("stdio", 0)`.
 *
 * Once pledge is in effect, the chmod functions (if allowed) will not
 * permit the sticky/setuid/setgid bits to change. Linux will EPERM here
 * and OpenBSD should ignore those three bits rather than crashing.
 *
 * User and group IDs can't be changed once pledge is in effect. OpenBSD
 * should ignore chown without crashing; whereas Linux will just EPERM.
 *
 * Memory functions won't permit creating executable code after pledge.
 * Restrictions on origin of SYSCALL instructions will become enforced
 * on Linux (cf. msyscall) after pledge too, which means the process
 * gets killed if SYSCALL is used outside the .privileged section. One
 * exception is if the "exec" group is specified, in which case these
 * restrictions need to be loosened.
 *
 * Using pledge is irreversible. On Linux it causes PR_SET_NO_NEW_PRIVS
 * to be set on your process; however, if "id" or "recvfd" are allowed
 * then then they theoretically could permit the gaining of some new
 * privileges. You may call pledge() multiple times if "stdio" is
 * allowed. In that case, the process can only move towards a more
 * restrictive state.
 *
 * pledge() can't filter file system paths or internet addresses. For
 * example, if you enable a category like "inet" then your process will
 * be able to talk to any internet address. The same applies to
 * categories like "wpath" and "cpath"; if enabled, any path the
 * effective user id is permitted to change will be changeable.
 *
 * `promises` is a string that may include any of the following groups
 * delimited by spaces.
 *
 * - "stdio" allows exit, close, dup, dup2, dup3, fchdir, fstat, fsync,
 *   fdatasync, ftruncate, getdents, getegid, getrandom, geteuid,
 *   getgid, getgroups, getitimer, getpgid, getpgrp, getpid, getppid,
 *   getresgid, getresuid, getrlimit, getsid, wait4, gettimeofday,
 *   getuid, lseek, madvise, brk, arch_prctl, uname, set_tid_address,
 *   clock_getres, clock_gettime, clock_nanosleep, mmap (PROT_EXEC and
 *   weird flags aren't allowed), mprotect (PROT_EXEC isn't allowed),
 *   msync, munmap, nanosleep, pipe, pipe2, read, readv, pread, recv,
 *   poll, recvfrom, preadv, write, writev, pwrite, pwritev, select,
 *   send, sendto (only if addr is null), setitimer, shutdown, sigaction
 *   (but SIGSYS is forbidden), sigaltstack, sigprocmask, sigreturn,
 *   sigsuspend, umask, socketpair, ioctl(FIONREAD), ioctl(FIONBIO),
 *   ioctl(FIOCLEX), ioctl(FIONCLEX), fcntl(F_GETFD), fcntl(F_SETFD),
 *   fcntl(F_GETFL), fcntl(F_SETFL).
 *
 * - "rpath" (read-only path ops) allows chdir, getcwd, open(O_RDONLY),
 *   openat(O_RDONLY), stat, fstat, lstat, fstatat, access, faccessat,
 *   readlink, readlinkat, statfs, fstatfs.
 *
 * - "wpath" (write path ops) allows getcwd, open(O_WRONLY),
 *   openat(O_WRONLY), stat, fstat, lstat, fstatat, access, faccessat,
 *   readlink, readlinkat, chmod, fchmod, fchmodat.
 *
 * - "cpath" (create path ops) allows open(O_CREAT), openat(O_CREAT),
 *   rename, renameat, renameat2, link, linkat, symlink, symlinkat,
 *   unlink, rmdir, unlinkat, mkdir, mkdirat.
 *
 * - "dpath" (create special path ops) allows mknod, mknodat, mkfifo.
 *
 * - "flock" allows flock, fcntl(F_GETLK), fcntl(F_SETLK),
 *   fcntl(F_SETLKW).
 *
 * - "tty" allows ioctl(TIOCGWINSZ), ioctl(TCGETS), ioctl(TCSETS),
 *   ioctl(TCSETSW), ioctl(TCSETSF).
 *
 * - "recvfd" allows recvmsg(SCM_RIGHTS).
 *
 * - "fattr" allows chmod, fchmod, fchmodat, utime, utimes, futimens,
 *   utimensat.
 *
 * - "inet" allows socket(AF_INET), listen, bind, connect, accept,
 *   accept4, getpeername, getsockname, setsockopt, getsockopt, sendto.
 *
 * - "unix" allows socket(AF_UNIX), listen, bind, connect, accept,
 *   accept4, getpeername, getsockname, setsockopt, getsockopt.
 *
 * - "dns" allows socket(AF_INET), sendto, recvfrom, connect.
 *
 * - "proc" allows fork, vfork, kill, getpriority, setpriority, prlimit,
 *   setrlimit, setpgid, setsid.
 *
 * - "thread" allows clone, futex, and permits PROT_EXEC in mprotect.
 *
 * - "id" allows setuid, setreuid, setresuid, setgid, setregid,
 *   setresgid, setgroups, prlimit, setrlimit, getpriority, setpriority,
 *   setfsuid, setfsgid.
 *
 * - "exec" allows execve, execveat, access, faccessat. On Linux this
 *   also weakens some security to permit running APE binaries. However
 *   on OpenBSD they must be assimilate beforehand. On Linux, mmap()
 *   will be loosened up to allow creating PROT_EXEC memory (for APE
 *   loader) and system call origin verification won't be activated.
 *
 * - "execnative" allows execve, execveat. Can only be used to run
 *   native executables; you won't be able to run APE binaries. mmap()
 *   and mprotect() are still prevented from creating executable memory.
 *   System call origin verification can't be enabled. If you always
 *   assimilate your APE binaries, then this should be preferred.
 *
 * @return 0 on success, or -1 w/ errno
 * @raise ENOSYS if host os isn't Linux or OpenBSD
 * @raise EINVAL if `execpromises` is used on Linux
 */
int pledge(const char *promises, const char *execpromises) {
  int rc;
  if (IsLinux()) {
    rc = sys_pledge_linux(promises, execpromises);
  } else {
    rc = sys_pledge(promises, execpromises);
    if (!rc) {
      SetPromises(promises);
    }
  }
  STRACE("pledge(%#s, %#s) → %d% m", promises, execpromises, rc);
  return rc;
}