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https://github.com/idouble/nasm-assembly-linux-notes

🐧 Assembly with Linux (Notes, Syscalls, Protection Rings) 🐧
https://github.com/idouble/nasm-assembly-linux-notes

assembly kernel-mode kernel-module linux linux-kernel nasm nasm-assembly privilege-levels privileged-instruction protection-ring read ring-0 ring-3 ring0 ring3 syscalls systemcall systemcalls usermode write

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🐧 Assembly with Linux (Notes, Syscalls, Protection Rings) 🐧

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# 🐧 NASM Assembly Linux Notes 🐧

🐧 Assembly with **Linux** (Notes, **Syscalls**, **Protection Rings**) 🐧



## 🐧 System Calls Linux (Syscalls) 🐧



![System Calls Linux Assembly NASM ASM](Images/systemcalls_linux_kernel.png)



### ❓ What is a System Call? ❓



When you run a program which calls **open, fork, read, write** (and many others) you are making a **System Call**.



**System Calls** are how a program enters the kernel to perform some task. Programs use **System Calls** to perform a variety of operations such as: **creating processes, doing network and file IO**, and much more.



Example: A user running a word processor in **User Mode (Ring 3)** presses “save”: a **System Call** is made into **Kernel Mode (Ring 0)**, asking the **Kernel** to save the file.



## 📖 System Call Table (Syscall Table) 📖



 

 

 

 

 

 

 

 

 

 

  #

  Name

  Registers

  

  

 

 

  eax

  ebx

  ecx

  edx

  esi

  edi

  

 

 

  0

  sys_restart_syscall

  0x00

  -

  -

  -

  -

  -

  

 

 

  1

  sys_exit

  0x01

  int error_code

  -

  -

  -

  -

  

 

 

  2

  sys_fork

  0x02

  struct pt_regs *

  -

  -

  -

  -

  

 

 

  3

  sys_read

  0x03

  unsigned int fd

  char __user *buf

  size_t count

  -

  -

  

 

 

  4

  sys_write

  0x04

  unsigned int fd

  const char __user *buf

  size_t count

  -

  -

  

 

 

  5

  sys_open

  0x05

  const char __user *filename

  int flags

  int mode

  -

  -

  

 

 

  6

  sys_close

  0x06

  unsigned int fd

  -

  -

  -

  -

  

 

 

  7

  sys_waitpid

  0x07

  pid_t pid

  int __user *stat_addr

  int options

  -

  -

  

 

 

  8

  sys_creat

  0x08

  const char __user *pathname

  int mode

  -

  -

  -

  

 

 

  9

  sys_link

  0x09

  const char __user *oldname

  const char __user *newname

  -

  -

  -

  

 

 

  10

  sys_unlink

  0x0a

  const char __user *pathname

  -

  -

  -

  -

  

 

 

  11

  sys_execve

  0x0b

  char __user *

  char __user *__user *

  char __user *__user *

  struct pt_regs *

  -

  

 

 

  12

  sys_chdir

  0x0c

  const char __user *filename

  -

  -

  -

  -

  

 

 

  13

  sys_time

  0x0d

  time_t __user *tloc

  -

  -

  -

  -

  

 

 

  14

  sys_mknod

  0x0e

  const char __user *filename

  int mode

  unsigned dev

  -

  -

  

 

 

  15

  sys_chmod

  0x0f

  const char __user *filename

  mode_t mode

  -

  -

  -

  

 

 

  16

  sys_lchown16

  0x10

  const char __user *filename

  old_uid_t user

  old_gid_t group

  -

  -

  

 

 

  17

  not implemented

  0x11

  -

  -

  -

  -

  -

  

 

 

  18

  sys_stat

  0x12

  char __user *filename

  struct __old_kernel_stat __user *statbuf

  -

  -

  -

  

 

 

  19

  sys_lseek

  0x13

  unsigned int fd

  off_t offset

  unsigned int origin

  -

  -

  

 

 

  20

  sys_getpid

  0x14

  -

  -

  -

  -

  -

  

 

 

  21

  sys_mount

  0x15

  char __user *dev_name

  char __user *dir_name

  char __user *type

  unsigned long flags

  void __user *data

  

 

 

  22

  sys_oldumount

  0x16

  char __user *name

  -

  -

  -

  -

  

 

 

  23

  sys_setuid16

  0x17

  old_uid_t uid

  -

  -

  -

  -

  

 

 

  24

  sys_getuid16

  0x18

  -

  -

  -

  -

  -

  

 

 

  25

  sys_stime

  0x19

  time_t __user *tptr

  -

  -

  -

  -

  

 

 

  26

  sys_ptrace

  0x1a

  long request

  long pid

  long addr

  long data

  -

  

 

 

  27

  sys_alarm

  0x1b

  unsigned int seconds

  -

  -

  -

  -

  

 

 

  28

  sys_fstat

  0x1c

  unsigned int fd

  struct __old_kernel_stat __user *statbuf

  -

  -

  -

  

 

 

  29

  sys_pause

  0x1d

  -

  -

  -

  -

  -

  

 

 

  30

  sys_utime

  0x1e

  char __user *filename

  struct utimbuf __user *times

  -

  -

  -

  

 

 

  31

  not implemented

  0x1f

  -

  -

  -

  -

  -

  

 

 

  32

  not implemented

  0x20

  -

  -

  -

  -

  -

  

 

 

  33

  sys_access

  0x21

  const char __user *filename

  int mode

  -

  -

  -

  

 

 

  34

  sys_nice

  0x22

  int increment

  -

  -

  -

  -

  

 

 

  35

  not implemented

  0x23

  -

  -

  -

  -

  -

  

 

 

  36

  sys_sync

  0x24

  -

  -

  -

  -

  -

  

 

 

  37

  sys_kill

  0x25

  int pid

  int sig

  -

  -

  -

  

 

 

  38

  sys_rename

  0x26

  const char __user *oldname

  const char __user *newname

  -

  -

  -

  

 

 

  39

  sys_mkdir

  0x27

  const char __user *pathname

  int mode

  -

  -

  -

  

 

 

  40

  sys_rmdir

  0x28

  const char __user *pathname

  -

  -

  -

  -

  

 

 

  41

  sys_dup

  0x29

  unsigned int fildes

  -

  -

  -

  -

  

 

 

  42

  sys_pipe

  0x2a

  int __user *fildes

  -

  -

  -

  -

  

 

 

  43

  sys_times

  0x2b

  struct tms __user *tbuf

  -

  -

  -

  -

  

 

 

  44

  not implemented

  0x2c

  -

  -

  -

  -

  -

  

 

 

  45

  sys_brk

  0x2d

  unsigned long brk

  -

  -

  -

  -

  

 

 

  46

  sys_setgid16

  0x2e

  old_gid_t gid

  -

  -

  -

  -

  

 

 

  47

  sys_getgid16

  0x2f

  -

  -

  -

  -

  -

  

 

 

  48

  sys_signal

  0x30

  int sig

  __sighandler_t handler

  -

  -

  -

  

 

 

  49

  sys_geteuid16

  0x31

  -

  -

  -

  -

  -

  

 

 

  50

  sys_getegid16

  0x32

  -

  -

  -

  -

  -

  

 

 

  51

  sys_acct

  0x33

  const char __user *name

  -

  -

  -

  -

  

 

 

  52

  sys_umount

  0x34

  char __user *name

  int flags

  -

  -

  -

  

 

 

  53

  not implemented

  0x35

  -

  -

  -

  -

  -

  

 

 

  54

  sys_ioctl

  0x36

  unsigned int fd

  unsigned int cmd

  unsigned long arg

  -

  -

  

 

 

  55

  sys_fcntl

  0x37

  unsigned int fd

  unsigned int cmd

  unsigned long arg

  -

  -

  

 

 

  56

  not implemented

  0x38

  -

  -

  -

  -

  -

  

 

 

  57

  sys_setpgid

  0x39

  pid_t pid

  pid_t pgid

  -

  -

  -

  

 

 

  58

  not implemented

  0x3a

  -

  -

  -

  -

  -

  

 

 

  59

  sys_olduname

  0x3b

  struct oldold_utsname __user *

  -

  -

  -

  -

  

 

 

  60

  sys_umask

  0x3c

  int mask

  -

  -

  -

  -

  

 

 

  61

  sys_chroot

  0x3d

  const char __user *filename

  -

  -

  -

  -

  

 

 

  62

  sys_ustat

  0x3e

  unsigned dev

  struct ustat __user *ubuf

  -

  -

  -

  

 

 

  63

  sys_dup2

  0x3f

  unsigned int oldfd

  unsigned int newfd

  -

  -

  -

  

 

 

  64

  sys_getppid

  0x40

  -

  -

  -

  -

  -

  

 

 

  65

  sys_getpgrp

  0x41

  -

  -

  -

  -

  -

  

 

 

  66

  sys_setsid

  0x42

  -

  -

  -

  -

  -

  

 

 

  67

  sys_sigaction

  0x43

  int sig

  const struct old_sigaction __user *act

  struct old_sigaction __user *oact

  -

  -

  

 

 

  68

  sys_sgetmask

  0x44

  -

  -

  -

  -

  -

  

 

 

  69

  sys_ssetmask

  0x45

  int newmask

  -

  -

  -

  -

  

 

 

  70

  sys_setreuid16

  0x46

  old_uid_t ruid

  old_uid_t euid

  -

  -

  -

  

 

 

  71

  sys_setregid16

  0x47

  old_gid_t rgid

  old_gid_t egid

  -

  -

  -

  

 

 

  72

  sys_sigsuspend

  0x48

  int history0

  int history1

  old_sigset_t mask

  -

  -

  

 

 

  73

  sys_sigpending

  0x49

  old_sigset_t __user *set

  -

  -

  -

  -

  

 

 

  74

  sys_sethostname

  0x4a

  char __user *name

  int len

  -

  -

  -

  

 

 

  75

  sys_setrlimit

  0x4b

  unsigned int resource

  struct rlimit __user *rlim

  -

  -

  -

  

 

 

  76

  sys_old_getrlimit

  0x4c

  unsigned int resource

  struct rlimit __user *rlim

  -

  -

  -

  

 

 

  77

  sys_getrusage

  0x4d

  int who

  struct rusage __user *ru

  -

  -

  -

  

 

 

  78

  sys_gettimeofday

  0x4e

  struct timeval __user *tv

  struct timezone __user *tz

  -

  -

  -

  

 

 

  79

  sys_settimeofday

  0x4f

  struct timeval __user *tv

  struct timezone __user *tz

  -

  -

  -

  

 

 

  80

  sys_getgroups16

  0x50

  int gidsetsize

  old_gid_t __user *grouplist

  -

  -

  -

  

 

 

  81

  sys_setgroups16

  0x51

  int gidsetsize

  old_gid_t __user *grouplist

  -

  -

  -

  

 

 

  82

  sys_old_select

  0x52

  struct sel_arg_struct __user *arg

  -

  -

  -

  -

  

 

 

  83

  sys_symlink

  0x53

  const char __user *old

  const char __user *new

  -

  -

  -

  

 

 

  84

  sys_lstat

  0x54

  char __user *filename

  struct __old_kernel_stat __user *statbuf

  -

  -

  -

  

 

 

  85

  sys_readlink

  0x55

  const char __user *path

  char __user *buf

  int bufsiz

  -

  -

  

 

 

  86

  sys_uselib

  0x56

  const char __user *library

  -

  -

  -

  -

  

 

 

  87

  sys_swapon

  0x57

  const char __user *specialfile

  int swap_flags

  -

  -

  -

  

 

 

  88

  sys_reboot

  0x58

  int magic1

  int magic2

  unsigned int cmd

  void __user *arg

  -

  

 

 

  89

  sys_old_readdir

  0x59

  unsigned int

  struct old_linux_dirent __user *

  unsigned int

  -

  -

  

 

 

  90

  sys_old_mmap

  0x5a

  struct mmap_arg_struct __user *arg

  -

  -

  -

  -

  

 

 

  91

  sys_munmap

  0x5b

  unsigned long addr

  size_t len

  -

  -

  -

  

 

 

  92

  sys_truncate

  0x5c

  const char __user *path

  long length

  -

  -

  -

  

 

 

  93

  sys_ftruncate

  0x5d

  unsigned int fd

  unsigned long length

  -

  -

  -

  

 

 

  94

  sys_fchmod

  0x5e

  unsigned int fd

  mode_t mode

  -

  -

  -

  

 

 

  95

  sys_fchown16

  0x5f

  unsigned int fd

  old_uid_t user

  old_gid_t group

  -

  -

  

 

 

  96

  sys_getpriority

  0x60

  int which

  int who

  -

  -

  -

  

 

 

  97

  sys_setpriority

  0x61

  int which

  int who

  int niceval

  -

  -

  

 

 

  98

  not implemented

  0x62

  -

  -

  -

  -

  -

  

 

 

  99

  sys_statfs

  0x63

  const char __user * path

  struct statfs __user *buf

  -

  -

  -

  

 

 

  100

  sys_fstatfs

  0x64

  unsigned int fd

  struct statfs __user *buf

  -

  -

  -

  

 

 

  101

  sys_ioperm

  0x65

  unsigned long

  unsigned long

  int

  -

  -

  

 

 

  102

  sys_socketcall

  0x66

  int call

  unsigned long __user *args

  -

  -

  -

  

 

 

  103

  sys_syslog

  0x67

  int type

  char __user *buf

  int len

  -

  -

  

 

 

  104

  sys_setitimer

  0x68

  int which

  struct itimerval __user *value

  struct itimerval __user *ovalue

  -

  -

  

 

 

  105

  sys_getitimer

  0x69

  int which

  struct itimerval __user *value

  -

  -

  -

  

 

 

  106

  sys_newstat

  0x6a

  char __user *filename

  struct stat __user *statbuf

  -

  -

  -

  

 

 

  107

  sys_newlstat

  0x6b

  char __user *filename

  struct stat __user *statbuf

  -

  -

  -

  

 

 

  108

  sys_newfstat

  0x6c

  unsigned int fd

  struct stat __user *statbuf

  -

  -

  -

  

 

 

  109

  sys_uname

  0x6d

  struct old_utsname __user *

  -

  -

  -

  -

  

 

 

  110

  sys_iopl

  0x6e

  unsigned int

  struct pt_regs *

  -

  -

  -

  

 

 

  111

  sys_vhangup

  0x6f

  -

  -

  -

  -

  -

  

 

 

  112

  not implemented

  0x70

  -

  -

  -

  -

  -

  

 

 

  113

  sys_vm86old

  0x71

  struct vm86_struct __user *

  struct pt_regs *

  -

  -

  -

  

 

 

  114

  sys_wait4

  0x72

  pid_t pid

  int __user *stat_addr

  int options

  struct rusage __user *ru

  -

  

 

 

  115

  sys_swapoff

  0x73

  const char __user *specialfile

  -

  -

  -

  -

  

 

 

  116

  sys_sysinfo

  0x74

  struct sysinfo __user *info

  -

  -

  -

  -

  

 

 

  117

  sys_ipc

  0x75

  -

  -

  -

  -

  -

  

 

 

  118

  sys_fsync

  0x76

  unsigned int fd

  -

  -

  -

  -

  

 

 

  119

  sys_sigreturn

  0x77

  struct pt_regs *regs

  -

  -

  -

  -

  

 

 

  120

  sys_clone

  0x78

  unsigned long

  unsigned long

  unsigned long

  unsigned long

  struct pt_regs *

  

 

 

  121

  sys_setdomainname

  0x79

  char __user *name

  int len

  -

  -

  -

  

 

 

  122

  sys_newuname

  0x7a

  struct new_utsname __user *name

  -

  -

  -

  -

  

 

 

  123

  sys_modify_ldt

  0x7b

  int

  void __user *

  unsigned long

  -

  -

  

 

 

  124

  sys_adjtimex

  0x7c

  struct timex __user *txc_p

  -

  -

  -

  -

  

 

 

  125

  sys_mprotect

  0x7d

  unsigned long start

  size_t len

  unsigned long prot

  -

  -

  

 

 

  126

  sys_sigprocmask

  0x7e

  int how

  old_sigset_t __user *set

  old_sigset_t __user *oset

  -

  -

  

 

 

  127

  not implemented

  0x7f

  -

  -

  -

  -

  -

  

 

 

  128

  sys_init_module

  0x80

  void __user *umod

  unsigned long len

  const char __user *uargs

  -

  -

  

 

 

  129

  sys_delete_module

  0x81

  const char __user *name_user

  unsigned int flags

  -

  -

  -

  

 

 

  130

  not implemented

  0x82

  -

  -

  -

  -

  -

  

 

 

  131

  sys_quotactl

  0x83

  unsigned int cmd

  const char __user *special

  qid_t id

  void __user *addr

  -

  

 

 

  132

  sys_getpgid

  0x84

  pid_t pid

  -

  -

  -

  -

  

 

 

  133

  sys_fchdir

  0x85

  unsigned int fd

  -

  -

  -

  -

  

 

 

  134

  sys_bdflush

  0x86

  int func

  long data

  -

  -

  -

  

 

 

  135

  sys_sysfs

  0x87

  int option

  unsigned long arg1

  unsigned long arg2

  -

  -

  

 

 

  136

  sys_personality

  0x88

  unsigned int personality

  -

  -

  -

  -

  

 

 

  137

  not implemented

  0x89

  -

  -

  -

  -

  -

  

 

 

  138

  sys_setfsuid16

  0x8a

  old_uid_t uid

  -

  -

  -

  -

  

 

 

  139

  sys_setfsgid16

  0x8b

  old_gid_t gid

  -

  -

  -

  -

  

 

 

  140

  sys_llseek

  0x8c

  unsigned int fd

  unsigned long offset_high

  unsigned long offset_low

  loff_t __user *result

  unsigned int origin

  

 

 

  141

  sys_getdents

  0x8d

  unsigned int fd

  struct linux_dirent __user *dirent

  unsigned int count

  -

  -

  

 

 

  142

  sys_select

  0x8e

  int n

  fd_set __user *inp

  fd_set __user *outp

  fd_set __user *exp

  struct timeval __user *tvp

  

 

 

  143

  sys_flock

  0x8f

  unsigned int fd

  unsigned int cmd

  -

  -

  -

  

 

 

  144

  sys_msync

  0x90

  unsigned long start

  size_t len

  int flags

  -

  -

  

 

 

  145

  sys_readv

  0x91

  unsigned long fd

  const struct iovec __user *vec

  unsigned long vlen

  -

  -

  

 

 

  146

  sys_writev

  0x92

  unsigned long fd

  const struct iovec __user *vec

  unsigned long vlen

  -

  -

  

 

 

  147

  sys_getsid

  0x93

  pid_t pid

  -

  -

  -

  -

  

 

 

  148

  sys_fdatasync

  0x94

  unsigned int fd

  -

  -

  -

  -

  

 

 

  149

  sys_sysctl

  0x95

  struct __sysctl_args __user *args

  -

  -

  -

  -

  

 

 

  150

  sys_mlock

  0x96

  unsigned long start

  size_t len

  -

  -

  -

  

 

 

  151

  sys_munlock

  0x97

  unsigned long start

  size_t len

  -

  -

  -

  

 

 

  152

  sys_mlockall

  0x98

  int flags

  -

  -

  -

  -

  

 

 

  153

  sys_munlockall

  0x99

  -

  -

  -

  -

  -

  

 

 

  154

  sys_sched_setparam

  0x9a

  pid_t pid

  struct sched_param __user *param

  -

  -

  -

  

 

 

  155

  sys_sched_getparam

  0x9b

  pid_t pid

  struct sched_param __user *param

  -

  -

  -

  

 

 

  156

  sys_sched_setscheduler

  0x9c

  pid_t pid

  int policy

  struct sched_param __user *param

  -

  -

  

 

 

  157

  sys_sched_getscheduler

  0x9d

  pid_t pid

  -

  -

  -

  -

  

 

 

  158

  sys_sched_yield

  0x9e

  -

  -

  -

  -

  -

  

 

 

  159

  sys_sched_get_priority_max

  0x9f

  int policy

  -

  -

  -

  -

  

 

 

  160

  sys_sched_get_priority_min

  0xa0

  int policy

  -

  -

  -

  -

  

 

 

  161

  sys_sched_rr_get_interval

  0xa1

  pid_t pid

  struct timespec __user *interval

  -

  -

  -

  

 

 

  162

  sys_nanosleep

  0xa2

  struct timespec __user *rqtp

  struct timespec __user *rmtp

  -

  -

  -

  

 

 

  163

  sys_mremap

  0xa3

  unsigned long addr

  unsigned long old_len

  unsigned long new_len

  unsigned long flags

  unsigned long new_addr

  

 

 

  164

  sys_setresuid16

  0xa4

  old_uid_t ruid

  old_uid_t euid

  old_uid_t suid

  -

  -

  

 

 

  165

  sys_getresuid16

  0xa5

  old_uid_t __user *ruid

  old_uid_t __user *euid

  old_uid_t __user *suid

  -

  -

  

 

 

  166

  sys_vm86

  0xa6

  unsigned long

  unsigned long

  struct pt_regs *

  -

  -

  

 

 

  167

  not implemented

  0xa7

  -

  -

  -

  -

  -

  

 

 

  168

  sys_poll

  0xa8

  struct pollfd __user *ufds

  unsigned int nfds

  long timeout

  -

  -

  

 

 

  169

  sys_nfsservctl

  0xa9

  int cmd

  struct nfsctl_arg __user *arg

  void __user *res

  -

  -

  

 

 

  170

  sys_setresgid16

  0xaa

  old_gid_t rgid

  old_gid_t egid

  old_gid_t sgid

  -

  -

  

 

 

  171

  sys_getresgid16

  0xab

  old_gid_t __user *rgid

  old_gid_t __user *egid

  old_gid_t __user *sgid

  -

  -

  

 

 

  172

  sys_prctl

  0xac

  int option

  unsigned long arg2

  unsigned long arg3

  unsigned long arg4

  unsigned long arg5

  

 

 

  173

  sys_rt_sigreturn

  0xad

  struct pt_regs *

  -

  -

  -

  -

  

 

 

  174

  sys_rt_sigaction

  0xae

  int sig

  const struct sigaction __user *act

  struct sigaction __user *oact

  size_t sigsetsize

  -

  

 

 

  175

  sys_rt_sigprocmask

  0xaf

  int how

  sigset_t __user *set

  sigset_t __user *oset

  size_t sigsetsize

  -

  

 

 

  176

  sys_rt_sigpending

  0xb0

  sigset_t __user *set

  size_t sigsetsize

  -

  -

  -

  

 

 

  177

  sys_rt_sigtimedwait

  0xb1

  const sigset_t __user *uthese

  siginfo_t __user *uinfo

  const struct timespec __user *uts

  size_t sigsetsize

  -

  

 

 

  178

  sys_rt_sigqueueinfo

  0xb2

  int pid

  int sig

  siginfo_t __user *uinfo

  -

  -

  

 

 

  179

  sys_rt_sigsuspend

  0xb3

  sigset_t __user *unewset

  size_t sigsetsize

  -

  -

  -

  

 

 

  180

  sys_pread64

  0xb4

  unsigned int fd

  char __user *buf

  size_t count

  loff_t pos

  -

  

 

 

  181

  sys_pwrite64

  0xb5

  unsigned int fd

  const char __user *buf

  size_t count

  loff_t pos

  -

  

 

 

  182

  sys_chown16

  0xb6

  const char __user *filename

  old_uid_t user

  old_gid_t group

  -

  -

  

 

 

  183

  sys_getcwd

  0xb7

  char __user *buf

  unsigned long size

  -

  -

  -

  

 

 

  184

  sys_capget

  0xb8

  cap_user_header_t header

  cap_user_data_t dataptr

  -

  -

  -

  

 

 

  185

  sys_capset

  0xb9

  cap_user_header_t header

  const cap_user_data_t data

  -

  -

  -

  

 

 

  186

  sys_sigaltstack

  0xba

  const stack_t __user *

  stack_t __user *

  struct pt_regs *

  -

  -

  

 

 

  187

  sys_sendfile

  0xbb

  int out_fd

  int in_fd

  off_t __user *offset

  size_t count

  -

  

 

 

  188

  not implemented

  0xbc

  -

  -

  -

  -

  -

  

 

 

  189

  not implemented

  0xbd

  -

  -

  -

  -

  -

  

 

 

  190

  sys_vfork

  0xbe

  struct pt_regs *

  -

  -

  -

  -

  

 

 

  191

  sys_getrlimit

  0xbf

  unsigned int resource

  struct rlimit __user *rlim

  -

  -

  -

  

 

 

  192

  sys_mmap_pgoff

  0xc0

  -

  -

  -

  -

  -

  

 

 

  193

  sys_truncate64

  0xc1

  const char __user *path

  loff_t length

  -

  -

  -

  

 

 

  194

  sys_ftruncate64

  0xc2

  unsigned int fd

  loff_t length

  -

  -

  -

  

 

 

  195

  sys_stat64

  0xc3

  char __user *filename

  struct stat64 __user *statbuf

  -

  -

  -

  

 

 

  196

  sys_lstat64

  0xc4

  char __user *filename

  struct stat64 __user *statbuf

  -

  -

  -

  

 

 

  197

  sys_fstat64

  0xc5

  unsigned long fd

  struct stat64 __user *statbuf

  -

  -

  -

  

 

 

  198

  sys_lchown

  0xc6

  const char __user *filename

  uid_t user

  gid_t group

  -

  -

  

 

 

  199

  sys_getuid

  0xc7

  -

  -

  -

  -

  -

  

 

 

  200

  sys_getgid

  0xc8

  -

  -

  -

  -

  -

  

 

 

  201

  sys_geteuid

  0xc9

  -

  -

  -

  -

  -

  

 

 

  202

  sys_getegid

  0xca

  -

  -

  -

  -

  -

  

 

 

  203

  sys_setreuid

  0xcb

  uid_t ruid

  uid_t euid

  -

  -

  -

  

 

 

  204

  sys_setregid

  0xcc

  gid_t rgid

  gid_t egid

  -

  -

  -

  

 

 

  205

  sys_getgroups

  0xcd

  int gidsetsize

  gid_t __user *grouplist

  -

  -

  -

  

 

 

  206

  sys_setgroups

  0xce

  int gidsetsize

  gid_t __user *grouplist

  -

  -

  -

  

 

 

  207

  sys_fchown

  0xcf

  unsigned int fd

  uid_t user

  gid_t group

  -

  -

  

 

 

  208

  sys_setresuid

  0xd0

  uid_t ruid

  uid_t euid

  uid_t suid

  -

  -

  

 

 

  209

  sys_getresuid

  0xd1

  uid_t __user *ruid

  uid_t __user *euid

  uid_t __user *suid

  -

  -

  

 

 

  210

  sys_setresgid

  0xd2

  gid_t rgid

  gid_t egid

  gid_t sgid

  -

  -

  

 

 

  211

  sys_getresgid

  0xd3

  gid_t __user *rgid

  gid_t __user *egid

  gid_t __user *sgid

  -

  -

  

 

 

  212

  sys_chown

  0xd4

  const char __user *filename

  uid_t user

  gid_t group

  -

  -

  

 

 

  213

  sys_setuid

  0xd5

  uid_t uid

  -

  -

  -

  -

  

 

 

  214

  sys_setgid

  0xd6

  gid_t gid

  -

  -

  -

  -

  

 

 

  215

  sys_setfsuid

  0xd7

  uid_t uid

  -

  -

  -

  -

  

 

 

  216

  sys_setfsgid

  0xd8

  gid_t gid

  -

  -

  -

  -

  

 

 

  217

  sys_pivot_root

  0xd9

  const char __user *new_root

  const char __user *put_old

  -

  -

  -

  

 

 

  218

  sys_mincore

  0xda

  unsigned long start

  size_t len

  unsigned char __user * vec

  -

  -

  

 

 

  219

  sys_madvise

  0xdb

  unsigned long start

  size_t len

  int behavior

  -

  -

  

 

 

  220

  sys_getdents64

  0xdc

  unsigned int fd

  struct linux_dirent64 __user *dirent

  unsigned int count

  -

  -

  

 

 

  221

  sys_fcntl64

  0xdd

  unsigned int fd

  unsigned int cmd

  unsigned long arg

  -

  -

  

 

 

  222

  not implemented

  0xde

  -

  -

  -

  -

  -

  

 

 

  223

  not implemented

  0xdf

  -

  -

  -

  -

  -

  

 

 

  224

  sys_gettid

  0xe0

  -

  -

  -

  -

  -

  

 

 

  225

  sys_readahead

  0xe1

  int fd

  loff_t offset

  size_t count

  -

  -

  

 

 

  226

  sys_setxattr

  0xe2

  const char __user *path

  const char __user *name

  const void __user *value

  size_t size

  int flags

  

 

 

  227

  sys_lsetxattr

  0xe3

  const char __user *path

  const char __user *name

  const void __user *value

  size_t size

  int flags

  

 

 

  228

  sys_fsetxattr

  0xe4

  int fd

  const char __user *name

  const void __user *value

  size_t size

  int flags

  

 

 

  229

  sys_getxattr

  0xe5

  const char __user *path

  const char __user *name

  void __user *value

  size_t size

  -

  

 

 

  230

  sys_lgetxattr

  0xe6

  const char __user *path

  const char __user *name

  void __user *value

  size_t size

  -

  

 

 

  231

  sys_fgetxattr

  0xe7

  int fd

  const char __user *name

  void __user *value

  size_t size

  -

  

 

 

  232

  sys_listxattr

  0xe8

  const char __user *path

  char __user *list

  size_t size

  -

  -

  

 

 

  233

  sys_llistxattr

  0xe9

  const char __user *path

  char __user *list

  size_t size

  -

  -

  

 

 

  234

  sys_flistxattr

  0xea

  int fd

  char __user *list

  size_t size

  -

  -

  

 

 

  235

  sys_removexattr

  0xeb

  const char __user *path

  const char __user *name

  -

  -

  -

  

 

 

  236

  sys_lremovexattr

  0xec

  const char __user *path

  const char __user *name

  -

  -

  -

  

 

 

  237

  sys_fremovexattr

  0xed

  int fd

  const char __user *name

  -

  -

  -

  

 

 

  238

  sys_tkill

  0xee

  int pid

  int sig

  -

  -

  -

  

 

 

  239

  sys_sendfile64

  0xef

  int out_fd

  int in_fd

  loff_t __user *offset

  size_t count

  -

  

 

 

  240

  sys_futex

  0xf0

  -

  -

  -

  -

  -

  

 

 

  241

  sys_sched_setaffinity

  0xf1

  pid_t pid

  unsigned int len

  unsigned long __user

  *user_mask_ptr

  -

  -

  

 

 

  242

  sys_sched_getaffinity

  0xf2

  pid_t pid

  unsigned int len

  unsigned long __user

  *user_mask_ptr

  -

  -

  

 

 

  243

  sys_set_thread_area

  0xf3

  struct user_desc __user *

  -

  -

  -

  -

  

 

 

  244

  sys_get_thread_area

  0xf4

  struct user_desc __user *

  -

  -

  -

  -

  

 

 

  245

  sys_io_setup

  0xf5

  unsigned nr_reqs

  aio_context_t __user *ctx

  -

  -

  -

  

 

 

  246

  sys_io_destroy

  0xf6

  aio_context_t ctx

  -

  -

  -

  -

  

 

 

  247

  sys_io_getevents

  0xf7

  aio_context_t ctx_id

  long min_nr

  long nr

  struct io_event __user *events

  struct timespec __user *timeout

  

 

 

  248

  sys_io_submit

  0xf8

  aio_context_t

  long

  struct iocb __user * __user *

  -

  -

  

 

 

  249

  sys_io_cancel

  0xf9

  aio_context_t ctx_id

  struct iocb __user *iocb

  struct io_event __user *result

  -

  -

  

 

 

  250

  sys_fadvise64

  0xfa

  int fd

  loff_t offset

  size_t len

  int advice

  -

  

 

 

  251

  not implemented

  0xfb

  -

  -

  -

  -

  -

  

 

 

  252

  sys_exit_group

  0xfc

  int error_code

  -

  -

  -

  -

  

 

 

  253

  sys_lookup_dcookie

  0xfd

  u64 cookie64

  char __user *buf

  size_t len

  -

  -

  

 

 

  254

  sys_epoll_create

  0xfe

  int size

  -

  -

  -

  -

  

 

 

  255

  sys_epoll_ctl

  0xff

  int epfd

  int op

  int fd

  struct epoll_event __user *event

  -

  

 

 

  256

  sys_epoll_wait

  0x100

  int epfd

  struct epoll_event __user *events

  int maxevents

  int timeout

  -

  

 

 

  257

  sys_remap_file_pages

  0x101

  unsigned long start

  unsigned long size

  unsigned long prot

  unsigned long pgoff

  unsigned long flags

  

 

 

  258

  sys_set_tid_address

  0x102

  int __user *tidptr

  -

  -

  -

  -

  

 

 

  259

  sys_timer_create

  0x103

  clockid_t which_clock

  struct sigevent __user *timer_event_spec

  timer_t __user *

  created_timer_id

  -

  -

  

 

 

  260

  sys_timer_settime

  0x104

  timer_t timer_id

  int flags

  const struct itimerspec __user *new_setting

  struct itimerspec __user *old_setting

  -

  

 

 

  261

  sys_timer_gettime

  0x105

  timer_t timer_id

  struct itimerspec __user *setting

  -

  -

  -

  

 

 

  262

  sys_timer_getoverrun

  0x106

  timer_t timer_id

  -

  -

  -

  -

  

 

 

  263

  sys_timer_delete

  0x107

  timer_t timer_id

  -

  -

  -

  -

  

 

 

  264

  sys_clock_settime

  0x108

  clockid_t which_clock

  const struct timespec __user *tp

  -

  -

  -

  

 

 

  265

  sys_clock_gettime

  0x109

  clockid_t which_clock

  struct timespec __user *tp

  -

  -

  -

  

 

 

  266

  sys_clock_getres

  0x10a

  clockid_t which_clock

  struct timespec __user *tp

  -

  -

  -

  

 

 

  267

  sys_clock_nanosleep

  0x10b

  clockid_t which_clock

  int flags

  const struct timespec __user *rqtp

  struct timespec __user *rmtp

  -

  

 

 

  268

  sys_statfs64

  0x10c

  const char __user *path

  size_t sz

  struct statfs64 __user *buf

  -

  -

  

 

 

  269

  sys_fstatfs64

  0x10d

  unsigned int fd

  size_t sz

  struct statfs64 __user *buf

  -

  -

  

 

 

  270

  sys_tgkill

  0x10e

  int tgid

  int pid

  int sig

  -

  -

  

 

 

  271

  sys_utimes

  0x10f

  char __user *filename

  struct timeval __user *utimes

  -

  -

  -

  

 

 

  272

  sys_fadvise64_64

  0x110

  int fd

  loff_t offset

  loff_t len

  int advice

  -

  

 

 

  273

  not implemented

  0x111

  -

  -

  -

  -

  -

  

 

 

  274

  sys_mbind

  0x112

  -

  -

  -

  -

  -

  

 

 

  275

  sys_get_mempolicy

  0x113

  int __user *policy

  unsigned long __user *nmask

  unsigned long maxnode

  unsigned long addr

  unsigned long flags

  

 

 

  276

  sys_set_mempolicy

  0x114

  int mode

  unsigned long __user *nmask

  unsigned long maxnode

  -

  -

  

 

 

  277

  sys_mq_open

  0x115

  const char __user *name

  int oflag

  mode_t mode

  struct mq_attr __user *attr

  -

  

 

 

  278

  sys_mq_unlink

  0x116

  const char __user *name

  -

  -

  -

  -

  

 

 

  279

  sys_mq_timedsend

  0x117

  mqd_t mqdes

  const char __user *msg_ptr

  size_t msg_len

  unsigned int msg_prio

  const struct timespec __user

  *abs_timeout

 

 

  280

  sys_mq_timedreceive

  0x118

  mqd_t mqdes

  char __user *msg_ptr

  size_t msg_len

  unsigned int __user *msg_prio

  const struct timespec __user

  *abs_timeout

 

 

  281

  sys_mq_notify

  0x119

  mqd_t mqdes

  const struct sigevent __user *notification

  -

  -

  -

  

 

 

  282

  sys_mq_getsetattr

  0x11a

  mqd_t mqdes

  const struct mq_attr __user *mqstat

  struct mq_attr __user *omqstat

  -

  -

  

 

 

  283

  sys_kexec_load

  0x11b

  unsigned long entry

  unsigned long nr_segments

  struct kexec_segment __user *segments

  unsigned long flags

  -

  

 

 

  284

  sys_waitid

  0x11c

  int which

  pid_t pid

  struct siginfo __user *infop

  int options

  struct rusage __user *ru

  

 

 

  285

  not implemented

  0x11d

  -

  -

  -

  -

  -

  

 

 

  286

  sys_add_key

  0x11e

  const char __user *_type

  const char __user *_description

  const void __user *_payload

  size_t plen

  key_serial_t destringid

  

 

 

  287

  sys_request_key

  0x11f

  const char __user *_type

  const char __user *_description

  const char __user *_callout_info

  key_serial_t destringid

  -

  

 

 

  288

  sys_keyctl

  0x120

  int cmd

  unsigned long arg2

  unsigned long arg3

  unsigned long arg4

  unsigned long arg5

  

 

 

  289

  sys_ioprio_set

  0x121

  int which

  int who

  int ioprio

  -

  -

  

 

 

  290

  sys_ioprio_get

  0x122

  int which

  int who

  -

  -

  -

  

 

 

  291

  sys_inotify_init

  0x123

  -

  -

  -

  -

  -

  

 

 

  292

  sys_inotify_add_watch

  0x124

  int fd

  const char __user *path

  u32 mask

  -

  -

  

 

 

  293

  sys_inotify_rm_watch

  0x125

  int fd

  __s32 wd

  -

  -

  -

  

 

 

  294

  sys_migrate_pages

  0x126

  pid_t pid

  unsigned long maxnode

  const unsigned long __user *from

  const unsigned long __user *to

  -

  

 

 

  295

  sys_openat

  0x127

  int dfd

  const char __user *filename

  int flags

  int mode

  -

  

 

 

  296

  sys_mkdirat

  0x128

  int dfd

  const char __user * pathname

  int mode

  -

  -

  

 

 

  297

  sys_mknodat

  0x129

  int dfd

  const char __user * filename

  int mode

  unsigned dev

  -

  

 

 

  298

  sys_fchownat

  0x12a

  int dfd

  const char __user *filename

  uid_t user

  gid_t group

  int flag

  

 

 

  299

  sys_futimesat

  0x12b

  int dfd

  char __user *filename

  struct timeval __user *utimes

  -

  -

  

 

 

  300

  sys_fstatat64

  0x12c

  int dfd

  char __user *filename

  struct stat64 __user *statbuf

  int flag

  -

  

 

 

  301

  sys_unlinkat

  0x12d

  int dfd

  const char __user * pathname

  int flag

  -

  -

  

 

 

  302

  sys_renameat

  0x12e

  int olddfd

  const char __user * oldname

  int newdfd

  const char __user * newname

  -

  

 

 

  303

  sys_linkat

  0x12f

  int olddfd

  const char __user *oldname

  int newdfd

  const char __user *newname

  int flags

  

 

 

  304

  sys_symlinkat

  0x130

  const char __user * oldname

  int newdfd

  const char __user * newname

  -

  -

  

 

 

  305

  sys_readlinkat

  0x131

  int dfd

  const char __user *path

  char __user *buf

  int bufsiz

  -

  

 

 

  306

  sys_fchmodat

  0x132

  int dfd

  const char __user * filename

  mode_t mode

  -

  -

  

 

 

  307

  sys_faccessat

  0x133

  int dfd

  const char __user *filename

  int mode

  -

  -

  

 

 

  308

  sys_pselect6

  0x134

  -

  -

  -

  -

  -

  

 

 

  309

  sys_ppoll

  0x135

  struct pollfd __user *ufds

  unsigned int nfds

  struct timespec __user *tsp

  const sigset_t __user *sigmask

  size_t sigsetsize

  

 

 

  310

  sys_unshare

  0x136

  unsigned long unshare_flags

  -

  -

  -

  -

  

 

 

  311

  sys_set_robust_list

  0x137

  struct robust_list_head __user *head

  size_t len

  -

  -

  -

  

 

 

  312

  sys_get_robust_list

  0x138

  int pid

  struct robust_list_head __user * __user

  *head_ptr

  size_t __user *len_ptr

  -

  -

  

 

 

  313

  sys_splice

  0x139

  -

  -

  -

  -

  -

  

 

 

  314

  sys_sync_file_range

  0x13a

  int fd

  loff_t offset

  loff_t nbytes

  unsigned int flags

  -

  

 

 

  315

  sys_tee

  0x13b

  int fdin

  int fdout

  size_t len

  unsigned int flags

  -

  

 

 

  316

  sys_vmsplice

  0x13c

  int fd

  const struct iovec __user *iov

  unsigned long nr_segs

  unsigned int flags

  -

  

 

 

  317

  sys_move_pages

  0x13d

  -

  -

  -

  -

  -

  

 

 

  318

  sys_getcpu

  0x13e

  unsigned __user *cpu

  unsigned __user *node

  struct getcpu_cache __user *cache

  -

  -

  

 

 

  319

  sys_epoll_pwait

  0x13f

  -

  -

  -

  -

  -

  

 

 

  320

  sys_utimensat

  0x140

  int dfd

  char __user *filename

  struct timespec __user *utimes

  int flags

  -

  

 

 

  321

  sys_signalfd

  0x141

  int ufd

  sigset_t __user *user_mask

  size_t sizemask

  -

  -

  

 

 

  322

  sys_timerfd_create

  0x142

  int clockid

  int flags

  -

  -

  -

  

 

 

  323

  sys_eventfd

  0x143

  unsigned int count

  -

  -

  -

  -

  

 

 

  324

  sys_fallocate

  0x144

  int fd

  int mode

  loff_t offset

  loff_t len

  -

  

 

 

  325

  sys_timerfd_settime

  0x145

  int ufd

  int flags

  const struct itimerspec __user *utmr

  struct itimerspec __user *otmr

  -

  

 

 

  326

  sys_timerfd_gettime

  0x146

  int ufd

  struct itimerspec __user *otmr

  -

  -

  -

  

 

 

  327

  sys_signalfd4

  0x147

  int ufd

  sigset_t __user *user_mask

  size_t sizemask

  int flags

  -

  

 

 

  328

  sys_eventfd2

  0x148

  unsigned int count

  int flags

  -

  -

  -

  

 

 

  329

  sys_epoll_create1

  0x149

  int flags

  -

  -

  -

  -

  

 

 

  330

  sys_dup3

  0x14a

  unsigned int oldfd

  unsigned int newfd

  int flags

  -

  -

  

 

 

  331

  sys_pipe2

  0x14b

  int __user *fildes

  int flags

  -

  -

  -

  

 

 

  332

  sys_inotify_init1

  0x14c

  int flags

  -

  -

  -

  -

  

 

 

  333

  sys_preadv

  0x14d

  unsigned long fd

  const struct iovec __user *vec

  unsigned long vlen

  unsigned long pos_l

  unsigned long pos_h

  

 

 

  334

  sys_pwritev

  0x14e

  unsigned long fd

  const struct iovec __user *vec

  unsigned long vlen

  unsigned long pos_l

  unsigned long pos_h

  

 

 

  335

  sys_rt_tgsigqueueinfo

  0x14f

  pid_t tgid

  pid_t pid

  int sig

  siginfo_t __user *uinfo

  -

  

 

 

  336

  sys_perf_event_open

  0x150

  struct perf_event_attr __user *attr_uptr

  pid_t pid

  int cpu

  int group_fd

  unsigned long flags

  

 

 

  337

  sys_recvmmsg

  0x151

  int fd

  struct mmsghdr __user *msg

  unsigned int vlen

  unsigned flags

  struct timespec __user *timeout

  

 

 

 

  

  

  

  

  

  

  

  

  

  

 

 



## 🔧 Simple System Call Example calling SYS_WRITE (kernel opcode 4) 🔧

At Line **17**: **mov     eax, 4      ; invoke SYS_WRITE (kernel opcode 4)**

```

; Hello World Program

; Compile with: nasm -f elf helloworld.asm

; Link with (64 bit systems require elf_i386 option): ld -m elf_i386 helloworld.o -o helloworld

; Run with: ./helloworld

 

SECTION .data

msg     db      'Hello World!', 0Ah     ; assign msg variable with your message string

 

SECTION .text

global  _start

 

_start:

 

    mov     edx, 13     ; number of bytes to write - one for each letter plus 0Ah (line feed character)

    mov     ecx, msg    ; move the memory address of our message string into ecx

    mov     ebx, 1      ; write to the STDOUT file

    mov     eax, 4      ; invoke SYS_WRITE (kernel opcode 4)

    int     80h

```

## 🐧 Protection Rings / Privilege Levels 🐧

The x86-64 CPUs have a concept called **Privilege Levels**. (also often called **Protection Rings**)

**Linux** only uses **Ring 0** and **3** for **Kernel Mode (Ring 0)** and **User Mode (Ring 3)**. Thus, all user mode processes, running when the system is in any run level execute in **Ring 3**, until they make a **System Call** into kernel code, which transitions the cpu to **Ring 0**.



1. The **Kernel** runs at the most **privileged level**, called **Ring 0**. **User programs** run at **Ring 3**.

2. **Ring 0** can execute any system instruction and is given full trust.

3. To enter **Kernel Mode (Ring 0)**, you must perform a **System Call**. (Another Way to use **Kernel Mode (Ring 0)** is by writing **Linux Kernel Modules** in C.)  *Additional Info: In Windows you usually program a **driver** in C to use Kernel Mode (Ring 0) and like **Linux**, Windows only uses **Ring 0** and **3** too.*



![Privilege_Levels System Calls Linux Assembly NASM ASM](Images/privilege_levels_linux.png)



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