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Kernel Syscalls
Contents
Note on these
Args go in their normal registers, like arg1 in R0, as usual. Syscall # goes in IP (that's intra-procedural, not instruction pointer!), a.k.a R12.
As in all ARM (i.e. also on Android) the kernel entry is accomplished by the SVC command (SWI in some debuggers and ARM dialects). On the kernel end, a low level CPU exception handler (fleh_swi) is installed as part of the ExceptionVectorsBase, and - upon issuing a SWI/SVC - control is transferred to that address. This handler can check the syscall number to distinguish between POSIX calls (non negative) and Mach traps (negative).
Unix
Usage
MOV IP, #x // number from following list into Intraprocedural, a.k.a. r12 SVC 0x80 // Formerly, SWI (software interrupt)
For example:
(gdb) disass chown 0x30d2ad54 <chown>: mov r12, #16 ; 0x10, being # of chown 0x30d2ad58 <chown+4>: svc 0x00000080
Most of these are the same as you would find in the XNU open source kernel, with ARM idiosyncrasies aside (and #372, ledger)
sysent
The system call table in XNU is known as "sysent", and is no longer a public symbol, for obvious reasons (e.g. syscall hooking). It is fairly straightforward, however, to find the sysent and its calls. While i0nic proposes a heuristic of finding the sysent based on the exported kdebug symbol, this is unreliable, as the symbol is no longer exported. A better way is to home in on the pattern of the struct sysent entries itself, i.e - as defined in bsd/sys/sysent.h:
struct sysent { /* system call table */
int16_t sy_narg; /* number of args */
int8_t sy_resv; /* reserved */
int8_t sy_flags; /* flags */
sy_call_t *sy_call; /* implementing function */
sy_munge_t *sy_arg_munge32; /* system call arguments munger for 32-bit process */
sy_munge_t *sy_arg_munge64; /* system call arguments munger for 64-bit process */
int32_t sy_return_type; /* system call return types */
uint16_t sy_arg_bytes; /* Total size of arguments in bytes for
* 32-bit system calls
*/
};
Because system calls arguments are set in stone, it is straightforward to write code to find the signature of the first few syscalls (syscall, exit, fork..), and from there calculate the other sysent entries. A program to do so reliable on iOS has, in fact, been written, and produces the following output for iOS 6.0b1:
List of system calls from iOS 6.0b3
note: Even though a syscall is present in the table, it does not in any way imply it is functional. Auditing, for example, is not enabled in iOS (no CONFIG_AUDIT in the XNU build). Most of these syscalls are the same as those of OS X, with the exception of ledger (which actually makes a comeback in OS X Mountain Lion), and 434+ (CONFIG_EMBEDDED).
A good reference on these can be found at [Wiley's OS X and iOS Internals book online appendix]
$ joker ~/Documents/projects/iOS.6.0b3.iPod4.kernel This is an ARM binary. Applying iOS kernel signatures Syscall names are @2780953 mach_trap_table offset in file (for patching purposes): 3064992 (0x2ec4a0) Sysent offset in file (for patching purposes): 3076288 (0x2ef0c0) ..This appears to be XNU 2107.2.9 Suppressing enosys (0x800b3429) 1. exit 801d4974 T 2. fork 801d786c T 3. read 801eb408 T 4. write 801eb7dc T 5. open 800b13a4 T 6. close 801cc9b0 T 7. wait4 801d55a8 T 9. link 800b18e8 T 10. unlink 800b1ff0 T 12. chdir 800b0c60 T 13. fchdir 800b0af0 T 14. mknod 800b14bc T 15. chmod 800b2b40 T 16. chown 800b2c9c T 18. getfsstat 800b088c T 20. getpid 801dc0f8 T 23. setuid 801dc3ac T 24. getuid 801dc17c T 25. geteuid 801dc18c T 26. ptrace 801e7fb0 T 27. recvmsg 8020a780 T 28. sendmsg 8020a2c8 T 29. recvfrom 8020a3ac T 30. accept 80209c80 T 31. getpeername 8020aa4c T 32. getsockname 8020a99c T 33. access 800b24ac T 34. chflags 800b2928 T 35. fchflags 800b29f0 T 36. sync 800b0320 T 37. kill 801dfcb8 T 39. getppid 801dc100 T 41. dup 801caa00 T 42. pipe 801eda68 T 43. getegid 801dc204 T 46. sigaction 801dedd4 T 47. getgid 801dc1f4 T 48. sigprocmask 801df318 T 49. getlogin 801dcfd4 T 50. setlogin 801dd04c T 51. acct 801c53e8 T 52. sigpending 801df4bc T 53. sigaltstack 801dfbfc T 54. ioctl 801ebba0 T 55. reboot 801e7f14 T 56. revoke 800b43f8 T 57. symlink 800b1b58 T 58. readlink 800b282c T 59. execve 801d4348 T 60. umask 800b43d0 T 61. chroot 800b0d30 T 65. msync 801d83bc T 66. vfork 801d6f04 T 73. munmap 801d8468 T 74. mprotect 801d849c T 75. madvise 801d8554 T 78. mincore 801d85c0 T 79. getgroups 801dc214 T 80. setgroups 801dcf18 T 81. getpgrp 801dc108 T 82. setpgid 801dc2b4 T 83. setitimer 801e79fc T 85. swapon 8021bd00 T 86. getitimer 801e78b4 T 89. getdtablesize 801ca5d8 T 90. dup2 801cae50 T 92. fcntl 801cb31c T 93. select 801ebe4c T 95. fsync 800b3238 T 96. setpriority 801dd380 T 97. socket 80209728 T 98. connect 80209ca0 T 100. getpriority 801dd274 T 104. bind 802097f4 T 105. setsockopt 8020a8b4 T 106. listen 80209960 T 111. sigsuspend 801df4e4 T 116. gettimeofday 801e76c4 T 117. getrusage 801de118 T 118. getsockopt 8020a918 T 120. readv 801eb694 T 121. writev 801eba34 T 122. settimeofday 801e7720 T 123. fchown 800b2dac T 124. fchmod 800b2c70 T 126. setreuid 801dc6f8 T 127. setregid 801dca8c T 128. rename 800b3428 T 131. flock 801ce108 T 132. mkfifo 800b1798 T 133. sendto 80209fec T 134. shutdown 8020a884 T 135. socketpair 80209e90 T 136. mkdir 800b3d1c T 137. rmdir 800b3d5c T 138. utimes 800b2e60 T 139. futimes 800b3034 T 140. adjtime 801e7824 T 142. gethostuuid 801ed528 T 147. setsid 801dc270 T 151. getpgid 801dc110 T 152. setprivexec 801dc0e0 T 153. pread 801eb5f8 T 154. pwrite 801eb954 T 157. statfs 800b03c0 T 158. fstatfs 800b0678 T 159. unmount 800afe88 T 165. quotactl 800b03bc T 167. mount 800af068 T 169. csops 801daebc T 170. 170 old table 801db3a8 T 173. waitid 801d59a0 T 180. kdebug_trace 801c2cb0 T 181. setgid 801dc890 T 182. setegid 801dc99c T 183. seteuid 801dc5fc T 184. sigreturn 8021e67c T 185. chud 8021d38c T 187. fdatasync 800b32b0 T 188. stat 800b2588 T 189. fstat 801ccee8 T 190. lstat 800b26d4 T 191. pathconf 800b27c8 T 192. fpathconf 801ccf44 T 194. getrlimit 801ddf60 T 195. setrlimit 801dd828 T 196. getdirentries 800b3f94 T 197. mmap 801d7eac T 199. lseek 800b2068 T 200. truncate 800b30b4 T 201. ftruncate 800b3174 T 202. __sysctl 801e2364 T 203. mlock 801d870c T 204. munlock 801d8764 T 205. undelete 800b1cf0 T 216. mkcomplex 800b12c4 T 220. getattrlist 8009b060 T 221. setattrlist 8009b0d8 T 222. getdirentriesattr 800b44e0 T 223. exchangedata 800b469c T 225. searchfs 800b48dc T 226. delete 800b202c T 227. copyfile 800b32cc T 228. fgetattrlist 80098488 T 229. fsetattrlist 8009b7e0 T 230. poll 801ec5b0 T 231. watchevent 801eced8 T 232. waitevent 801ed07c T 233. modwatch 801ed1ec T 234. getxattr 800b5550 T 235. fgetxattr 800b568c T 236. setxattr 800b578c T 237. fsetxattr 800b5898 T 238. removexattr 800b5994 T 239. fremovexattr 800b5a5c T 240. listxattr 800b5b1c T 241. flistxattr 800b5c00 T 242. fsctl 800b4dd4 T 243. initgroups 801dcd94 T 244. posix_spawn 801d341c T 245. ffsctl 800b5474 T 250. minherit 801d851c T 266. shm_open 8020e9a8 T 267. shm_unlink 8020f488 T 268. sem_open 8020de04 T 269. sem_close 8020e59c T 270. sem_unlink 8020e364 T 271. sem_wait 8020e5f0 T 272. sem_trywait 8020e6b8 T 273. sem_post 8020e75c T 274. sem_getvalue 8020e800 T 275. sem_init 8020e7f8 T 276. sem_destroy 8020e7fc T 277. open_extended 800b11d8 T 278. umask_extended 800b4380 T 279. stat_extended 800b2530 T 280. lstat_extended 800b267c T 281. fstat_extended 801ccccc T 282. chmod_extended 800b2a30 T 283. fchmod_extended 800b2b74 T 284. access_extended 800b21a0 T 285. settid 801dcc18 T 286. gettid 801dc19c T 287. setsgroups 801dcf28 T 288. getsgroups 801dc268 T 289. setwgroups 801dcf2c T 290. getwgroups 801dc26c T 291. mkfifo_extended 800b16f4 T 292. mkdir_extended 800b3b30 T 294. shared_region_check_np 8021c23c T 296. vm_pressure_monitor 8021c9a0 T 297. psynch_rw_longrdlock 80215844 T 298. psynch_rw_yieldwrlock 80215af0 T 299. psynch_rw_downgrade 80215af8 T 300. psynch_rw_upgrade 80215af4 T 301. psynch_mutexwait 80212a5c T 302. psynch_mutexdrop 80213a20 T 303. psynch_cvbroad 80213a74 T 304. psynch_cvsignal 80214058 T 305. psynch_cvwait 802144e0 T 306. psynch_rw_rdlock 80214c18 T 307. psynch_rw_wrlock 80215848 T 308. psynch_rw_unlock 80215afc T 309. psynch_rw_unlock2 80215df4 T 310. getsid 801dc140 T 311. settid_with_pid 801dccb8 T 312. psynch_cvclrprepost 80214b18 T 313. aio_fsync 801c5dcc T 314. aio_return 801c5fa4 T 315. aio_suspend 801c622c T 316. aio_cancel 801c5944 T 317. aio_error 801c5d20 T 318. aio_read 801c5f84 T 319. aio_write 801c6440 T 320. lio_listio 801c6460 T 322. iopolicysys 801de30c T 323. 323 8021a5c4 T 324. mlockall 801d87a0 T 325. munlockall 801d87a4 T 327. issetugid 801dc39c T 328. __pthread_kill 801df930 T 329. __pthread_sigmask 801df990 T 330. __sigwait 801dfa40 T 331. __disable_threadsignal 801df60c T 332. __pthread_markcancel 801df628 T 333. __pthread_canceled 801df670 T 334. __semwait_signal 801df810 T 336. proc_info 802184a8 T 338. stat64 800b25d4 T 339. fstat64 801ccf24 T 340. lstat64 800b2720 T 341. stat64_extended 800b2624 T 342. lstat64_extended 800b2770 T 343. fstat64_extended 801ccf08 T 344. getdirentries64 800b4340 T 345. statfs64 800b06e0 T 346. fstatfs64 800b0828 T 347. getfsstat64 800b0a38 T 348. __pthread_chdir 800b0d28 T 349. __pthread_fchdir 800b0c58 T 350. audit 801c1970 T 351. auditon 801c1974 T 353. getauid 801c1978 T 354. setauid 801c197c T 357. getaudit_addr 801c1980 T 358. setaudit_addr 801c1984 T 359. auditctl 801c1988 T 360. bsdthread_create 80216948 T 361. bsdthread_terminate 80216bc0 T 362. kqueue 801cf494 T 363. kevent 801cf514 T 364. lchown 800b2d94 T 365. stack_snapshot 801c5108 T 366. bsdthread_register 80216c24 T 367. workq_open 80217878 T 368. workq_kernreturn 80217ce0 T 369. kevent64 801cf7ac T 370. __old_semwait_signal 801df6e4 T 371. __old_semwait_signal_nocancel 801df718 T 372. thread_selfid 802181e4 T 373. ledger 801ed590 T 380. __mac_execve 801d4368 T 381. __mac_syscall 8027d008 T 382. __mac_get_file 8027ccb0 T 383. __mac_set_file 8027cef8 T 384. __mac_get_link 8027cdd4 T 385. __mac_set_link 8027cff8 T 386. __mac_get_proc 8027c7a4 T 387. __mac_set_proc 8027c864 T 388. __mac_get_fd 8027cb5c T 389. __mac_set_fd 8027cde4 T 390. __mac_get_pid 8027c6d8 T 391. __mac_get_lcid 8027c918 T 392. __mac_get_lctx 8027c9dc T 393. __mac_set_lctx 8027ca98 T 394. setlcid 801dd114 T 395. getlcid 801dd1fc T 396. read_nocancel 801eb428 T 397. write_nocancel 801eb7fc T 398. open_nocancel 800b1434 T 399. close_nocancel 801cc9cc T 400. wait4_nocancel 801d55c8 T 401. recvmsg_nocancel 8020a7a0 T 402. sendmsg_nocancel 8020a2e8 T 403. recvfrom_nocancel 8020a3cc T 404. accept_nocancel 802099a0 T 405. msync_nocancel 801d83d4 T 406. fcntl_nocancel 801cb33c T 407. select_nocancel 801ebe68 T 408. fsync_nocancel 800b32a8 T 409. connect_nocancel 80209cb8 T 410. sigsuspend_nocancel 801df5a0 T 411. readv_nocancel 801eb6b4 T 412. writev_nocancel 801eba54 T 413. sendto_nocancel 8020a00c T 414. pread_nocancel 801eb618 T 415. pwrite_nocancel 801eb974 T 416. waitid_nocancel 801d59bc T 417. poll_nocancel 801ec5d0 T 420. sem_wait_nocancel 8020e60c T 421. aio_suspend_nocancel 801c624c T 422. __sigwait_nocancel 801dfa78 T 423. __semwait_signal_nocancel 801df844 T 424. __mac_mount 800af08c T 425. __mac_get_mount 8027d200 T 426. __mac_getfsstat 800b08b0 T 427. fsgetpath 800b5ce4 T 428. audit_session_self 801c1964 T 429. audit_session_join 801c1968 T 430. fileport_makeport 801ce1ec T 431. fileport_makefd 801ce390 T 432. audit_session_port 801c196c T 433. pid_suspend 8021c018 T 434. pid_resume 8021c088 T 435. pid_hibernate 8021c100 T 436. pid_shutdown_sockets 8021c158 T 438. shared_region_map_and_slide_np 8021c7ec T 439. kas_info 8021c9e8 T ; Provides ASLR information to user space (intentionally crippled in iOS, works in ML) 440. memorystatus_control 801e60f0 T ; Controls memory status (JetSam) 441. guarded_open_np 801ce9cc T ; New in 6b3, maybe b2 442. guarded_close_np 801cead8 T ; New in 6b3, maybe b2
Mach
XNU also supports the Mach personality, which is distinct from that of the UNIX syscalls discussed above. Mach syscalls (on 32-bit systems like iOS) are encoded as negative numbers, which is clever, since POSIX system calls are all non-negative. For example, consider mach_msg_trap:
_mach_msg_trap:
0001a8b4 e1a0c00d mov ip, sp
0001a8b8 e92d0170 push {r4, r5, r6, r8}
0001a8bc e89c0070 ldm ip, {r4, r5, r6}
0001a8c0 e3e0c01e mvn ip, #30 @ 0x1e ; Move NEGATIVE -30 into IP (R12)
0001a8c4 ef000080 svc 0x00000080 ; issue a supervisor call
0001a8c8 e8bd0170 pop {r4, r5, r6, r8}
0001a8cc e12fff1e bx lr
..
_semaphore_signal_all_trap:
0001a8f8 e3e0c021 mvn ip, #33 @ 0x21 ; NEGATIVE -33 into IP (R12)
0001a8fc ef000080 svc 0x00000080
0001a900 e12fff1e bx lr
Mach system calls are commonly known as "traps", and are maintained in a Mach Trap table. iOS's fleh_swi handler (the kernel entry point on the other side of the "SWI" or "SVC" command) checks the system call number - if it is negative, it is flipped (2's complement), and interpreted as Mach trap instead.
mach_trap_table
In iOS 5.x, the mach_trap_table is not far from the page_size export, and right next to the trap names. kern_invalid is the equivalent of ENOSYS. All the traps are ARM Thumb. The joker binary can be used to find the Mach trap table, as well. The following shows iOS 6.0.b1's table:
$ ./joker -ls mach kernel.iPod4.iOS6.0b1 This is an ARM binary. Applying iOS kernel signatures mach_trap_table offset in file (for patching purposes): 3064992 (0x2ec4a0) Kern invalid should be 0x80027ec1. Ignoring those ..This appears to be XNU 2107.1.78 10 _kernelrpc_mach_vm_allocate_trap 80014460 T 12 _kernelrpc_mach_vm_deallocate_trap 800144cc T 14 _kernelrpc_mach_vm_protect_trap 80014510 T 16 _kernelrpc_mach_port_allocate_trap 80014564 T 17 _kernelrpc_mach_port_destroy_trap 800145b4 T 18 _kernelrpc_mach_port_deallocate_trap 800145f0 T 19 _kernelrpc_mach_port_mod_refs_trap 8001462c T 20 _kernelrpc_mach_port_move_member_trap 8001466c T 21 _kernelrpc_mach_port_insert_right_trap 800146b0 T 22 _kernelrpc_mach_port_insert_member_trap 80014710 T 23 _kernelrpc_mach_port_extract_member_trap 80014754 T 26 mach_reply_port 8001b5b4 T 27 thread_self_trap 8001b598 T 28 task_self_trap 8001b578 T 29 host_self_trap 80019910 T 31 mach_msg_trap 80014ec0 T 32 mach_msg_overwrite_trap 80014d20 T 33 semaphore_signal_trap 80027188 T 34 semaphore_signal_all_trap 8002720c T 35 semaphore_signal_thread_trap 80027114 T 36 semaphore_wait_trap 800274b0 T 37 semaphore_wait_signal_trap 80027658 T 38 semaphore_timedwait_trap 80027598 T 39 semaphore_timedwait_signal_trap 8002773c T 44 task_name_for_pid 8021a838 T 45 task_for_pid 8021a688 T 46 pid_for_task 8021a63c T 48 macx_swapon 8021b414 T 49 macx_swapoff 8021b668 T 51 macx_triggers 8021b3f4 T 52 macx_backing_store_suspend 8021b370 T 53 macx_backing_store_recovery 8021b318 T 58 pfz_exit 80027818 T 59 swtch_pri 800278e4 T 60 swtch 8002781c T 61 thread_switch 80027ad4 T 62 clock_sleep_trap 80017520 T 89 mach_timebase_info_trap 80016658 T 90 mach_wait_until_trap 80016d20 T 91 mk_timer_create_trap 8001f2f4 T 92 mk_timer_destroy_trap 8001f500 T 93 mk_timer_arm_trap 8001f544 T 94 mk_timer_cancel_trap 8001f5c8 T 100 iokit_user_client_trap 8026c11c T
