prctl(2) 맨 페이지 - 윈디하나의 솔라나라

개요

섹션
맨 페이지 이름
검색(S)

prctl(2)

PRCTL(2)                   Linux Programmer's Manual                  PRCTL(2)



NAME
       prctl - operations on a process

SYNOPSIS
       #include <sys/prctl.h>

       int prctl(int option, unsigned long arg2, unsigned long arg3,
                 unsigned long arg4, unsigned long arg5);

DESCRIPTION
       prctl()  is  called  with  a first argument describing what to do (with
       values defined in <linux/prctl.h>), and further arguments with  a  sig‐
       nificance depending on the first one.  The first argument can be:

       PR_CAP_AMBIENT (since Linux 4.3)
              Reads  or  changes  the  ambient  capability  set of the calling
              thread, according to the value of arg2, which must be one of the
              following:

              PR_CAP_AMBIENT_RAISE
                     The  capability specified in arg3 is added to the ambient
                     set.  The specified capability must already be present in
                     both  the  permitted  and  the  inheritable  sets  of the
                     process.   This  operation  is  not  permitted   if   the
                     SECBIT_NO_CAP_AMBIENT_RAISE securebit is set.

              PR_CAP_AMBIENT_LOWER
                     The  capability  specified  in  arg3  is removed from the
                     ambient set.

              PR_CAP_AMBIENT_IS_SET
                     The prctl() call returns 1 if the capability in  arg3  is
                     in the ambient set and 0 if it is not.

              PR_CAP_AMBIENT_CLEAR_ALL
                     All  capabilities  will  be removed from the ambient set.
                     This operation requires setting arg3 to zero.

              In all of the above operations, arg4 and arg5 must be  specified
              as 0.

              Higher-level  interfaces  layered on top of the above operations
              are  provided  in  the  libcap(3)  library  in   the   form   of
              cap_get_ambient(3),   cap_set_ambient(3),   and  cap_reset_ambi‐
              ent(3).

       PR_CAPBSET_READ (since Linux 2.6.25)
              Return (as the function result) 1 if the capability specified in
              arg2 is in the calling thread's capability bounding set, or 0 if
              it  is  not.   (The  capability   constants   are   defined   in
              <linux/capability.h>.)   The  capability  bounding  set dictates
              whether the process can receive the capability through a  file's
              permitted capability set on a subsequent call to execve(2).

              If  the capability specified in arg2 is not valid, then the call
              fails with the error EINVAL.

              A higher-level interface layered on top  of  this  operation  is
              provided   in   the   libcap(3)   library   in   the   form   of
              cap_get_bound(3).

       PR_CAPBSET_DROP (since Linux 2.6.25)
              If the calling thread has the CAP_SETPCAP capability within  its
              user  namespace, then drop the capability specified by arg2 from
              the calling thread's capability bounding set.  Any  children  of
              the calling thread will inherit the newly reduced bounding set.

              The  call fails with the error: EPERM if the calling thread does
              not have the CAP_SETPCAP; EINVAL if arg2 does  not  represent  a
              valid capability; or EINVAL if file capabilities are not enabled
              in the kernel, in which case bounding sets are not supported.

              A higher-level interface layered on top  of  this  operation  is
              provided   in   the   libcap(3)   library   in   the   form   of
              cap_drop_bound(3).

       PR_SET_CHILD_SUBREAPER (since Linux 3.4)
              If arg2 is nonzero, set the "child subreaper" attribute  of  the
              calling process; if arg2 is zero, unset the attribute.

              A subreaper fulfills the role of init(1) for its descendant pro‐
              cesses.  When a process becomes orphaned  (i.e.,  its  immediate
              parent  terminates)  then that process will be reparented to the
              nearest still living ancestor subreaper.  Subsequently, calls to
              getppid() in the orphaned process will now return the PID of the
              subreaper process, and when the orphan  terminates,  it  is  the
              subreaper process that will receive a SIGCHLD signal and will be
              able to wait(2) on the process to discover its termination  sta‐
              tus.

              The  setting of the "child subreaper" attribute is not inherited
              by children created by fork(2) and  clone(2).   The  setting  is
              preserved across execve(2).

              Establishing a subreaper process is useful in session management
              frameworks where a hierarchical group of processes is managed by
              a  subreaper  process  that needs to be informed when one of the
              processes—for example, a double-forked  daemon—terminates  (per‐
              haps  so that it can restart that process).  Some init(1) frame‐
              works (e.g., systemd(1)) employ a subreaper process for  similar
              reasons.

       PR_GET_CHILD_SUBREAPER (since Linux 3.4)
              Return the "child subreaper" setting of the caller, in the loca‐
              tion pointed to by (int *) arg2.

       PR_SET_DUMPABLE (since Linux 2.3.20)
              Set the state of the "dumpable" flag, which  determines  whether
              core dumps are produced for the calling process upon delivery of
              a signal whose default behavior is to produce a core dump.

              In kernels up to and including 2.6.12, arg2  must  be  either  0
              (SUID_DUMP_DISABLE,    process    is    not   dumpable)   or   1
              (SUID_DUMP_USER, process is dumpable).  Between  kernels  2.6.13
              and  2.6.17,  the  value  2 was also permitted, which caused any
              binary which normally would not be dumped to be dumped  readable
              by  root  only;  for  security  reasons,  this  feature has been
              removed.    (See   also   the   description   of   /proc/sys/fs/
              suid_dumpable in proc(5).)

              Normally,  this  flag  is set to 1.  However, it is reset to the
              current value contained in the  file  /proc/sys/fs/suid_dumpable
              (which  by  default  has  the value 0), in the following circum‐
              stances:

              *  The process's effective user or group ID is changed.

              *  The process's filesystem user or group  ID  is  changed  (see
                 credentials(7)).

              *  The  process executes (execve(2)) a set-user-ID or set-group-
                 ID program, resulting in a change  of  either  the  effective
                 user ID or the effective group ID.

              *  The  process  executes  (execve(2))  a  program that has file
                 capabilities (see capabilities(7)), but only if the permitted
                 capabilities  gained  exceed  those already permitted for the
                 process.

              Processes  that  are  not  dumpable  can  not  be  attached  via
              ptrace(2) PTRACE_ATTACH; see ptrace(2) for further details.

              If  a  process  is  not  dumpable, the ownership of files in the
              process's /proc/[pid] directory  is  affected  as  described  in
              proc(5).

       PR_GET_DUMPABLE (since Linux 2.3.20)
              Return (as the function result) the current state of the calling
              process's dumpable flag.

       PR_SET_ENDIAN (since Linux 2.6.18, PowerPC only)
              Set the endian-ness of the calling process to the value given in
              arg2,  which  should  be  one  of  the following: PR_ENDIAN_BIG,
              PR_ENDIAN_LITTLE, or PR_ENDIAN_PPC_LITTLE (PowerPC pseudo little
              endian).

       PR_GET_ENDIAN (since Linux 2.6.18, PowerPC only)
              Return  the  endian-ness of the calling process, in the location
              pointed to by (int *) arg2.

       PR_SET_FP_MODE (since Linux 4.0, only on MIPS)
              On the MIPS architecture, user-space code can be built using  an
              ABI  which  permits  linking with code that has more restrictive
              floating-point (FP) requirements.  For example, user-space  code
              may  be  built  to  target the O32 FPXX ABI and linked with code
              built for either one of the more restrictive FP32 or FP64  ABIs.
              When more restrictive code is linked in, the overall requirement
              for the process is to use the  more  restrictive  floating-point
              mode.

              Because the kernel has no means of knowing in advance which mode
              the process should be executed in, and  because  these  restric‐
              tions   can  change  over  the  lifetime  of  the  process,  the
              PR_SET_FP_MODE operation is provided to  allow  control  of  the
              floating-point mode from user space.

              The  (unsigned  int)  arg2 argument is a bit mask describing the
              floating-point mode used:

              PR_FP_MODE_FR
                     When this bit is unset (so called FR=0 or FR0 mode),  the
                     32  floating-point registers are 32 bits wide, and 64-bit
                     registers are represented as a pair of  registers  (even-
                     and  odd-  numbered, with the even-numbered register con‐
                     taining the lower 32 bits, and the odd-numbered  register
                     containing the higher 32 bits).

                     When  this  bit  is  set  (on supported hardware), the 32
                     floating-point registers are 64 bits wide (so called FR=1
                     or  FR1  mode).   Note  that  modern MIPS implementations
                     (MIPS R6 and newer) support FR=1 mode only.

                     Applications that use the O32 FP32 ABI can  operate  only
                     when  this  bit  is unset (FR=0; or they can be used with
                     FRE enabled, see below).  Applications that use  the  O32
                     FP64  ABI (and the O32 FP64A ABI, which exists to provide
                     the ability to  operate  with  existing  FP32  code;  see
                     below)  can  operate  only  when  this bit is set (FR=1).
                     Applications that use the O32 FPXX ABI can  operate  with
                     either FR=0 or FR=1.

              PR_FP_MODE_FRE
                     Enable  emulation  of  32-bit  floating-point mode.  When
                     this mode is enabled, it emulates  32-bit  floating-point
                     operations by raising a reserved-instruction exception on
                     every instruction that uses 32-bit formats and the kernel
                     then  handles  the instruction in software.  (The problem
                     lies in the discrepancy of handling  odd-numbered  regis‐
                     ters  which are the high 32 bits of 64-bit registers with
                     even numbers in FR=0 mode and the lower 32-bit  parts  of
                     odd-numbered  64-bit  registers  in FR=1 mode.)  Enabling
                     this bit is necessary when code with  the  O32  FP32  ABI
                     should  operate with code with compatible the O32 FPXX or
                     O32 FP64A ABIs (which require FR=1 FPU mode) or  when  it
                     is  executed  on  newer  hardware (MIPS R6 onwards) which
                     lacks FR=0 mode support when a binary with the  FP32  ABI
                     is used.

                     Note  that  this mode makes sense only when the FPU is in
                     64-bit mode (FR=1).

                     Note that the use of emulation inherently has a  signifi‐
                     cant performance hit and should be avoided if possible.

              In  the  N32/N64 ABI, 64-bit floating-point mode is always used,
              so FPU emulation is not required and the FPU always operates  in
              FR=1 mode.

              This  option  is  mainly  intended for use by the dynamic linker
              (ld.so(8)).

              The arguments arg3, arg4, and arg5 are ignored.

       PR_GET_FP_MODE (since Linux 4.0, only on MIPS)
              Get the current floating-point  mode  (see  the  description  of
              PR_SET_FP_MODE for details).

              On  success,  the  call  returns a bit mask which represents the
              current floating-point mode.

              The arguments arg2, arg3, arg4, and arg5 are ignored.

       PR_SET_FPEMU (since Linux 2.4.18, 2.5.9, only on ia64)
              Set  floating-point  emulation  control  bits  to  arg2.    Pass
              PR_FPEMU_NOPRINT  to  silently  emulate floating-point operation
              accesses, or PR_FPEMU_SIGFPE to not emulate floating-point oper‐
              ations and send SIGFPE instead.

       PR_GET_FPEMU (since Linux 2.4.18, 2.5.9, only on ia64)
              Return  floating-point  emulation  control bits, in the location
              pointed to by (int *) arg2.

       PR_SET_FPEXC (since Linux 2.4.21, 2.5.32, only on PowerPC)
              Set   floating-point   exception    mode    to    arg2.     Pass
              PR_FP_EXC_SW_ENABLE  to  use  FPEXC  for  FP  exception enables,
              PR_FP_EXC_DIV for floating-point divide by  zero,  PR_FP_EXC_OVF
              for  floating-point  overflow,  PR_FP_EXC_UND for floating-point
              underflow,  PR_FP_EXC_RES  for  floating-point  inexact  result,
              PR_FP_EXC_INV     for    floating-point    invalid    operation,
              PR_FP_EXC_DISABLED for FP exceptions disabled,  PR_FP_EXC_NONRE‐
              COV for async nonrecoverable exception mode, PR_FP_EXC_ASYNC for
              async recoverable exception mode, PR_FP_EXC_PRECISE for  precise
              exception mode.

       PR_GET_FPEXC (since Linux 2.4.21, 2.5.32, only on PowerPC)
              Return floating-point exception mode, in the location pointed to
              by (int *) arg2.

       PR_SET_KEEPCAPS (since Linux 2.2.18)
              Set the state of the calling thread's "keep capabilities"  flag.
              The  effect  of this flag is described in capabilities(7).  arg2
              must be either 0 (clear the flag) or  1  (set  the  flag).   The
              "keep capabilities" value will be reset to 0 on subsequent calls
              to execve(2).

       PR_GET_KEEPCAPS (since Linux 2.2.18)
              Return (as the function result) the current state of the calling
              thread's  "keep  capabilities"  flag.  See capabilities(7) for a
              description of this flag.

       PR_MCE_KILL (since Linux 2.6.32)
              Set the machine check memory  corruption  kill  policy  for  the
              calling  thread.  If arg2 is PR_MCE_KILL_CLEAR, clear the thread
              memory corruption kill policy and use the  system-wide  default.
              (The system-wide default is defined by /proc/sys/vm/memory_fail‐
              ure_early_kill; see proc(5).)  If arg2 is PR_MCE_KILL_SET, use a
              thread-specific  memory  corruption  kill policy.  In this case,
              arg3   defines   whether    the    policy    is    early    kill
              (PR_MCE_KILL_EARLY),  late  kill (PR_MCE_KILL_LATE), or the sys‐
              tem-wide default (PR_MCE_KILL_DEFAULT).  Early kill  means  that
              the  thread  receives a SIGBUS signal as soon as hardware memory
              corruption is detected inside its address space.  In  late  kill
              mode,  the  process  is killed only when it accesses a corrupted
              page.  See sigaction(2) for more information on the SIGBUS  sig‐
              nal.  The policy is inherited by children.  The remaining unused
              prctl() arguments must be zero for future compatibility.

       PR_MCE_KILL_GET (since Linux 2.6.32)
              Return the current per-process machine check kill  policy.   All
              unused prctl() arguments must be zero.

       PR_SET_MM (since Linux 3.3)
              Modify  certain kernel memory map descriptor fields of the call‐
              ing process.  Usually these fields are set  by  the  kernel  and
              dynamic loader (see ld.so(8) for more information) and a regular
              application should not use this  feature.   However,  there  are
              cases,  such  as  self-modifying programs, where a program might
              find it useful to change its own memory map.

              The calling process must have the  CAP_SYS_RESOURCE  capability.
              The  value  in arg2 is one of the options below, while arg3 pro‐
              vides a new value for the option.  The arg4 and  arg5  arguments
              must be zero if unused.

              Before  Linux 3.10, this feature is available only if the kernel
              is built with the CONFIG_CHECKPOINT_RESTORE option enabled.

              PR_SET_MM_START_CODE
                     Set the address above which the  program  text  can  run.
                     The  corresponding  memory area must be readable and exe‐
                     cutable, but not writable or shareable  (see  mprotect(2)
                     and mmap(2) for more information).

              PR_SET_MM_END_CODE
                     Set  the  address  below  which the program text can run.
                     The corresponding memory area must be readable  and  exe‐
                     cutable, but not writable or shareable.

              PR_SET_MM_START_DATA
                     Set the address above which initialized and uninitialized
                     (bss) data are placed.   The  corresponding  memory  area
                     must  be  readable  and  writable,  but not executable or
                     shareable.

              PR_SET_MM_END_DATA
                     Set the address below which initialized and uninitialized
                     (bss)  data  are  placed.   The corresponding memory area
                     must be readable and  writable,  but  not  executable  or
                     shareable.

              PR_SET_MM_START_STACK
                     Set  the  start  address of the stack.  The corresponding
                     memory area must be readable and writable.

              PR_SET_MM_START_BRK
                     Set the address above  which  the  program  heap  can  be
                     expanded  with  brk(2) call.  The address must be greater
                     than the ending address of the current program data  seg‐
                     ment.   In  addition,  the combined size of the resulting
                     heap and the size of the data segment  can't  exceed  the
                     RLIMIT_DATA resource limit (see setrlimit(2)).

              PR_SET_MM_BRK
                     Set  the  current brk(2) value.  The requirements for the
                     address are  the  same  as  for  the  PR_SET_MM_START_BRK
                     option.

              The following options are available since Linux 3.5.

              PR_SET_MM_ARG_START
                     Set  the  address above which the program command line is
                     placed.

              PR_SET_MM_ARG_END
                     Set the address below which the program command  line  is
                     placed.

              PR_SET_MM_ENV_START
                     Set  the  address  above which the program environment is
                     placed.

              PR_SET_MM_ENV_END
                     Set the address below which the  program  environment  is
                     placed.

                     The     address    passed    with    PR_SET_MM_ARG_START,
                     PR_SET_MM_ARG_END,        PR_SET_MM_ENV_START,        and
                     PR_SET_MM_ENV_END  should belong to a process stack area.
                     Thus, the corresponding memory  area  must  be  readable,
                     writable,  and  (depending  on  the kernel configuration)
                     have the MAP_GROWSDOWN attribute set (see mmap(2)).

              PR_SET_MM_AUXV
                     Set a new auxiliary vector.   The  arg3  argument  should
                     provide  the address of the vector.  The arg4 is the size
                     of the vector.

              PR_SET_MM_EXE_FILE
                     Supersede the /proc/pid/exe symbolic link with a new  one
                     pointing  to a new executable file identified by the file
                     descriptor provided in arg3 argument.  The file  descrip‐
                     tor should be obtained with a regular open(2) call.

                     To  change  the  symbolic  link,  one  needs to unmap all
                     existing executable memory areas, including those created
                     by the kernel itself (for example the kernel usually cre‐
                     ates at least one executable  memory  area  for  the  ELF
                     .text section).

                     In  Linux  4.9 and earlier, the PR_SET_MM_EXE_FILE opera‐
                     tion can be performed only once in a process's  lifetime;
                     attempting to perform the operation a second time results
                     in the error EPERM.  This restriction  was  enforced  for
                     security  reasons that were subsequently deemed specious,
                     and the restriction was removed  in  Linux  4.10  because
                     some user-space applications needed to perform this oper‐
                     ation more than once.

              The following options are available since Linux 3.18.

              PR_SET_MM_MAP
                     Provides one-shot access to all the addresses by  passing
                     in a struct prctl_mm_map (as defined in <linux/prctl.h>).
                     The arg4 argument should provide the size of the struct.

                     This feature is available only if  the  kernel  is  built
                     with the CONFIG_CHECKPOINT_RESTORE option enabled.

              PR_SET_MM_MAP_SIZE
                     Returns  the  size  of the struct prctl_mm_map the kernel
                     expects.  This allows user space  to  find  a  compatible
                     struct.   The  arg4  argument  should  be a pointer to an
                     unsigned int.

                     This feature is available only if  the  kernel  is  built
                     with the CONFIG_CHECKPOINT_RESTORE option enabled.

       PR_MPX_ENABLE_MANAGEMENT, PR_MPX_DISABLE_MANAGEMENT (since Linux 3.19)
              Enable  or disable kernel management of Memory Protection eXten‐
              sions (MPX) bounds tables.  The arg2, arg3, arg4, and arg5 argu‐
              ments must be zero.

              MPX  is  a  hardware-assisted  mechanism  for  performing bounds
              checking on pointers.  It consists of a set of registers storing
              bounds  information  and  a  set of special instruction prefixes
              that tell the CPU on which  instructions  it  should  do  bounds
              enforcement.   There  is a limited number of these registers and
              when there are more pointers than registers, their contents must
              be  "spilled"  into  a  set  of tables.  These tables are called
              "bounds tables" and the MPX prctl() operations  control  whether
              the kernel manages their allocation and freeing.

              When management is enabled, the kernel will take over allocation
              and freeing of the bounds tables.  It does this by trapping  the
              #BR exceptions that result at first use of missing bounds tables
              and instead of delivering the exception to user space, it  allo‐
              cates  the  table  and  populates  the bounds directory with the
              location of the new table.  For freeing, the  kernel  checks  to
              see  if  bounds tables are present for memory which is not allo‐
              cated, and frees them if so.

              Before enabling MPX management  using  PR_MPX_ENABLE_MANAGEMENT,
              the  application  must  first have allocated a user-space buffer
              for the bounds directory and placed the location of that  direc‐
              tory in the bndcfgu register.

              These  calls  fail  if  the  CPU or kernel does not support MPX.
              Kernel support for MPX is enabled via  the  CONFIG_X86_INTEL_MPX
              configuration  option.   You  can check whether the CPU supports
              MPX by looking for the 'mpx' CPUID bit, like with the  following
              command:

                  cat /proc/cpuinfo | grep ' mpx '

              A  thread  may  not switch in or out of long (64-bit) mode while
              MPX is enabled.

              All threads in a process are affected by these calls.

              The child of a fork(2) inherits the  state  of  MPX  management.
              During  execve(2),  MPX  management  is  reset  to a state as if
              PR_MPX_DISABLE_MANAGEMENT had been called.

              For further information on Intel MPX, see the kernel source file
              Documentation/x86/intel_mpx.txt.

       PR_SET_NAME (since Linux 2.6.9)
              Set the name of the calling thread, using the value in the loca‐
              tion pointed to by (char *) arg2.  The name  can  be  up  to  16
              bytes long, including the terminating null byte.  (If the length
              of the string, including the terminating null byte,  exceeds  16
              bytes,  the  string  is  silently  truncated.)  This is the same
              attribute  that  can  be  set  via   pthread_setname_np(3)   and
              retrieved  using  pthread_getname_np(3).  The attribute is like‐
              wise accessible via /proc/self/task/[tid]/comm, where tid is the
              name of the calling thread.

       PR_GET_NAME (since Linux 2.6.11)
              Return  the name of the calling thread, in the buffer pointed to
              by (char *) arg2.  The buffer should allow space for  up  to  16
              bytes; the returned string will be null-terminated.

       PR_SET_NO_NEW_PRIVS (since Linux 3.5)
              Set  the calling thread's no_new_privs attribute to the value in
              arg2.  With no_new_privs set to 1,  execve(2)  promises  not  to
              grant  privileges  to  do anything that could not have been done
              without the execve(2) call (for example, rendering the set-user-
              ID  and  set-group-ID mode bits, and file capabilities non-func‐
              tional).  Once set, this the no_new_privs  attribute  cannot  be
              unset.   The  setting of this attribute is inherited by children
              created by fork(2) and clone(2), and preserved across execve(2).

              Since Linux 4.10, the value of a thread's no_new_privs attribute
              can be viewed via the NoNewPrivs field in the /proc/[pid]/status
              file.

              For more information, see  the  kernel  source  file  Documenta‐
              tion/userspace-api/no_new_privs.rst        (or        Documenta‐
              tion/prctl/no_new_privs.txt before Linux 4.13).  See  also  sec‐
              comp(2).

       PR_GET_NO_NEW_PRIVS (since Linux 3.5)
              Return  (as  the  function result) the value of the no_new_privs
              attribute for the calling thread.  A value of  0  indicates  the
              regular  execve(2)  behavior.   A value of 1 indicates execve(2)
              will operate in the privilege-restricting mode described above.

       PR_SET_PDEATHSIG (since Linux 2.1.57)
              Set the parent-death signal  of  the  calling  process  to  arg2
              (either  a  signal value in the range 1..maxsig, or 0 to clear).
              This is the signal that the calling process will  get  when  its
              parent dies.

              Warning:  the  "parent"  in  this  case  is considered to be the
              thread that created this process.  In other  words,  the  signal
              will  be  sent  when  that  thread terminates (via, for example,
              pthread_exit(3)), rather than after all of the  threads  in  the
              parent process terminate.

              The  parent-death  signal is sent upon subsequent termination of
              the parent thread and also upon termination  of  each  subreaper
              process (see the description of PR_SET_CHILD_SUBREAPER above) to
              which the caller is  subsequently  reparented.   If  the  parent
              thread  and  all  ancestor subreapers have already terminated by
              the time of the PR_SET_PDEATHSIG operation, then no parent-death
              signal is sent to the caller.

              The parent-death signal is process-directed (see signal(7)) and,
              if the child installs a handler using the  sigaction(2)  SA_SIG‐
              INFO  flag,  the  si_pid  field of the siginfo_t argument of the
              handler contains the PID of the terminating parent process.

              The parent-death signal setting is cleared for the  child  of  a
              fork(2).   It is also (since Linux 2.4.36 / 2.6.23) cleared when
              executing a set-user-ID or set-group-ID binary, or a binary that
              has  associated  capabilities  (see capabilities(7)); otherwise,
              this value is preserved across execve(2).

       PR_GET_PDEATHSIG (since Linux 2.3.15)
              Return the current value of the parent process death signal,  in
              the location pointed to by (int *) arg2.

       PR_SET_PTRACER (since Linux 3.4)
              This is meaningful only when the Yama LSM is enabled and in mode
              1   ("restricted    ptrace",    visible    via    /proc/sys/ker‐
              nel/yama/ptrace_scope).   When  a "ptracer process ID" is passed
              in arg2, the caller is declaring that the  ptracer  process  can
              ptrace(2)  the  calling  process  as if it were a direct process
              ancestor.  Each PR_SET_PTRACER operation replaces  the  previous
              "ptracer process ID".  Employing PR_SET_PTRACER with arg2 set to
              0  clears  the  caller's  "ptracer  process  ID".   If  arg2  is
              PR_SET_PTRACER_ANY,  the  ptrace restrictions introduced by Yama
              are effectively disabled for the calling process.

              For further information, see the kernel source  file  Documenta‐
              tion/admin-guide/LSM/Yama.rst       (or      Documentation/secu‐
              rity/Yama.txt before Linux 4.13).

       PR_SET_SECCOMP (since Linux 2.6.23)
              Set the secure computing (seccomp) mode for the calling  thread,
              to limit the available system calls.  The more recent seccomp(2)
              system  call  provides  a  superset  of  the  functionality   of
              PR_SET_SECCOMP.

              The  seccomp  mode is selected via arg2.  (The seccomp constants
              are defined in <linux/seccomp.h>.)

              With arg2 set to SECCOMP_MODE_STRICT, the only system calls that
              the  thread is permitted to make are read(2), write(2), _exit(2)
              (but not exit_group(2)), and sigreturn(2).  Other  system  calls
              result  in the delivery of a SIGKILL signal.  Strict secure com‐
              puting mode is useful for number-crunching applications that may
              need to execute untrusted byte code, perhaps obtained by reading
              from a pipe or socket.  This operation is available only if  the
              kernel is configured with CONFIG_SECCOMP enabled.

              With arg2 set to SECCOMP_MODE_FILTER (since Linux 3.5), the sys‐
              tem calls allowed are defined by a pointer to a Berkeley  Packet
              Filter  passed  in  arg3.   This argument is a pointer to struct
              sock_fprog; it can be designed to filter arbitrary system  calls
              and  system  call arguments.  This mode is available only if the
              kernel is configured with CONFIG_SECCOMP_FILTER enabled.

              If SECCOMP_MODE_FILTER filters permit fork(2), then the  seccomp
              mode  is  inherited by children created by fork(2); if execve(2)
              is  permitted,  then  the  seccomp  mode  is  preserved   across
              execve(2).  If the filters permit prctl() calls, then additional
              filters can be added; they are run in order until the first non-
              allow result is seen.

              For  further  information, see the kernel source file Documenta‐
              tion/userspace-api/seccomp_filter.rst       (or       Documenta‐
              tion/prctl/seccomp_filter.txt before Linux 4.13).

       PR_GET_SECCOMP (since Linux 2.6.23)
              Return (as the function result) the secure computing mode of the
              calling thread.  If the caller is not in secure computing  mode,
              this operation returns 0; if the caller is in strict secure com‐
              puting mode, then the prctl() call will cause a  SIGKILL  signal
              to be sent to the process.  If the caller is in filter mode, and
              this system call is allowed by the seccomp filters,  it  returns
              2; otherwise, the process is killed with a SIGKILL signal.  This
              operation is available only if the  kernel  is  configured  with
              CONFIG_SECCOMP enabled.

              Since  Linux  3.8,  the  Seccomp field of the /proc/[pid]/status
              file provides a method of obtaining the same information,  with‐
              out the risk that the process is killed; see proc(5).

       PR_SET_SECUREBITS (since Linux 2.6.26)
              Set  the  "securebits"  flags of the calling thread to the value
              supplied in arg2.  See capabilities(7).

       PR_GET_SECUREBITS (since Linux 2.6.26)
              Return (as the function result) the "securebits"  flags  of  the
              calling thread.  See capabilities(7).

       PR_GET_SPECULATION_CTRL (since Linux 4.17)
              Returns  the  state  of  the speculation misfeature specified in
              arg2.  Currently, the only permitted value for this argument  is
              PR_SPEC_STORE_BYPASS  (otherwise  the  call fails with the error
              ENODEV).

              The return value uses bits 0-3 with the following meaning:

              PR_SPEC_PRCTL
                     Mitigation can be controlled per thread by  PR_SET_SPECU‐
                     LATION_CTRL

              PR_SPEC_ENABLE
                     The  speculation  feature  is enabled, mitigation is dis‐
                     abled.

              PR_SPEC_DISABLE
                     The  speculation  feature  is  disabled,  mitigation   is
                     enabled

              PR_SPEC_FORCE_DISABLE
                     Same as PR_SPEC_DISABLE but cannot be undone.

              If  all bits are 0, then the CPU is not affected by the specula‐
              tion misfeature.

              If PR_SPEC_PRCTL is set, then per-thread control of the  mitiga‐
              tion is available.  If not set, prctl() for the speculation mis‐
              feature will fail.

              The arg3, arg4, and arg5 arguments must be specified as 0;  oth‐
              erwise the call fails with the error EINVAL.

       PR_SET_SPECULATION_CTRL (since Linux 4.17)
              Sets  the state of the speculation misfeature specified in arg2.
              Currently,  the  only  permitted  value  for  this  argument  is
              PR_SPEC_STORE_BYPASS  (otherwise  the  call fails with the error
              ENODEV).  This setting is  a  per-thread  attribute.   The  arg3
              argument  is  used to hand in the control value, which is one of
              the following:

              PR_SPEC_ENABLE
                     The speculation feature is enabled,  mitigation  is  dis‐
                     abled.

              PR_SPEC_DISABLE
                     The   speculation  feature  is  disabled,  mitigation  is
                     enabled

              PR_SPEC_FORCE_DISABLE
                     Same as PR_SPEC_DISABLE but cannot be undone.   A  subse‐
                     quent prctl(..., PR_SPEC_ENABLE) will fail with the error
                     EPERM.

              Any other value in arg3 will result in the call failing with the
              error ERANGE.

              The  arg4  and  arg5 arguments must be specified as 0; otherwise
              the call fails with the error EINVAL.

              The  speculation  feature  can  also  be   controlled   by   the
              spec_store_bypass_disable  boot  parameter.   This parameter may
              enforce a read-only policy which will  result  in  the  prctl(2)
              call failing with the error ENXIO.  For further details, see the
              kernel  source   file   Documentation/admin-guide/kernel-parame‐
              ters.txt.

       PR_SET_THP_DISABLE (since Linux 3.15)
              Set  the state of the "THP disable" flag for the calling thread.
              If arg2 has a nonzero value, the flag is set,  otherwise  it  is
              cleared.   Setting  this  flag  provides  a method for disabling
              transparent huge pages for jobs where the code cannot  be  modi‐
              fied,  and  using a malloc hook with madvise(2) is not an option
              (i.e., statically allocated data).  The setting of the "THP dis‐
              able"  flag  is  inherited by a child created via fork(2) and is
              preserved across execve(2).

       PR_TASK_PERF_EVENTS_DISABLE (since Linux 2.6.31)
              Disable  all  performance  counters  attached  to  the   calling
              process, regardless of whether the counters were created by this
              process or another process.  Performance counters created by the
              calling  process  for  other processes are unaffected.  For more
              information on performance counters, see the Linux kernel source
              file tools/perf/design.txt.

              Originally    called    PR_TASK_PERF_COUNTERS_DISABLE;   renamed
              (retaining the same numerical value) in Linux 2.6.32.

       PR_TASK_PERF_EVENTS_ENABLE (since Linux 2.6.31)
              The converse of PR_TASK_PERF_EVENTS_DISABLE; enable  performance
              counters attached to the calling process.

              Originally called PR_TASK_PERF_COUNTERS_ENABLE; renamed in Linux
              2.6.32.

       PR_GET_THP_DISABLE (since Linux 3.15)
              Return (via the function result) the current setting of the "THP
              disable"  flag  for the calling thread: either 1, if the flag is
              set, or 0, if it is not.

       PR_GET_TID_ADDRESS (since Linux 3.5)
              Retrieve the clear_child_tid address set  by  set_tid_address(2)
              and  the  clone(2)  CLONE_CHILD_CLEARTID  flag,  in the location
              pointed to by (int **) arg2.  This feature is available only  if
              the  kernel  is  built with the CONFIG_CHECKPOINT_RESTORE option
              enabled.  Note that since the prctl() system call does not  have
              a compat implementation for the AMD64 x32 and MIPS n32 ABIs, and
              the kernel writes out a pointer using the kernel's pointer size,
              this operation expects a user-space buffer of 8 (not 4) bytes on
              these ABIs.

       PR_SET_TIMERSLACK (since Linux 2.6.28)
              Each thread has two associated timer slack values:  a  "default"
              value, and a "current" value.  This operation sets the "current"
              timer slack value for the calling thread.  arg2 is  an  unsigned
              long  value,  then  maximum "current" value is ULONG_MAX and the
              minimum "current" value is 1.  If the nanosecond value  supplied
              in arg2 is greater than zero, then the "current" value is set to
              this value.  If arg2 is equal to zero, the "current" timer slack
              is reset to the thread's "default" timer slack value.

              The  "current"  timer slack is used by the kernel to group timer
              expirations for  the  calling  thread  that  are  close  to  one
              another;  as a consequence, timer expirations for the thread may
              be up to the specified number  of  nanoseconds  late  (but  will
              never expire early).  Grouping timer expirations can help reduce
              system power consumption by minimizing CPU wake-ups.

              The timer expirations affected by timer slack are those  set  by
              select(2),   pselect(2),   poll(2),   ppoll(2),   epoll_wait(2),
              epoll_pwait(2), clock_nanosleep(2), nanosleep(2),  and  futex(2)
              (and thus the library functions implemented via futexes, includ‐
              ing    pthread_cond_timedwait(3),    pthread_mutex_timedlock(3),
              pthread_rwlock_timedrdlock(3),    pthread_rwlock_timedwrlock(3),
              and sem_timedwait(3)).

              Timer slack is not applied to threads that are scheduled under a
              real-time scheduling policy (see sched_setscheduler(2)).

              When  a  new  thread  is created, the two timer slack values are
              made the same as the "current" value  of  the  creating  thread.
              Thereafter,  a thread can adjust its "current" timer slack value
              via PR_SET_TIMERSLACK.  The "default" value  can't  be  changed.
              The timer slack values of init (PID 1), the ancestor of all pro‐
              cesses, are 50,000 nanoseconds  (50  microseconds).   The  timer
              slack  value is inherited by a child created via fork(2), and is
              preserved across execve(2).

              Since Linux 4.6, the "current" timer slack value of any  process
              can  be  examined  and  changed  via the file /proc/[pid]/timer‐
              slack_ns.  See proc(5).

       PR_GET_TIMERSLACK (since Linux 2.6.28)
              Return (as the function result) the "current" timer slack  value
              of the calling thread.

       PR_SET_TIMING (since Linux 2.6.0)
              Set  whether  to  use  (normal, traditional) statistical process
              timing or accurate timestamp-based process  timing,  by  passing
              PR_TIMING_STATISTICAL  or  PR_TIMING_TIMESTAMP to arg2.  PR_TIM‐
              ING_TIMESTAMP is not currently implemented  (attempting  to  set
              this mode will yield the error EINVAL).

       PR_GET_TIMING (since Linux 2.6.0)
              Return  (as  the function result) which process timing method is
              currently in use.

       PR_SET_TSC (since Linux 2.6.26, x86 only)
              Set the state of the  flag  determining  whether  the  timestamp
              counter  can be read by the process.  Pass PR_TSC_ENABLE to arg2
              to allow it to be read, or PR_TSC_SIGSEGV to generate a  SIGSEGV
              when the process tries to read the timestamp counter.

       PR_GET_TSC (since Linux 2.6.26, x86 only)
              Return  the  state of the flag determining whether the timestamp
              counter can be read, in the location pointed to by (int *) arg2.

       PR_SET_UNALIGN
              (Only on: ia64, since Linux 2.3.48; parisc, since Linux  2.6.15;
              PowerPC,  since  Linux  2.6.18;  Alpha,  since Linux 2.6.22; sh,
              since Linux 2.6.34; tile, since Linux 3.12) Set unaligned access
              control  bits  to arg2.  Pass PR_UNALIGN_NOPRINT to silently fix
              up unaligned user accesses,  or  PR_UNALIGN_SIGBUS  to  generate
              SIGBUS  on  unaligned user access.  Alpha also supports an addi‐
              tional flag with the value of 4 and no corresponding named  con‐
              stant,  which  instructs kernel to not fix up unaligned accesses
              (it is analogous to providing the UAC_NOFIX flag in  SSI_NVPAIRS
              operation of the setsysinfo() system call on Tru64).

       PR_GET_UNALIGN
              (see  PR_SET_UNALIGN  for  information on versions and architec‐
              tures) Return unaligned access control  bits,  in  the  location
              pointed to by (unsigned int *) arg2.

RETURN VALUE
       On   success,  PR_GET_DUMPABLE,  PR_GET_KEEPCAPS,  PR_GET_NO_NEW_PRIVS,
       PR_GET_THP_DISABLE, PR_CAPBSET_READ, PR_GET_TIMING,  PR_GET_TIMERSLACK,
       PR_GET_SECUREBITS,     PR_MCE_KILL_GET,     PR_CAP_AMBIENT+PR_CAP_AMBI‐
       ENT_IS_SET, and (if it returns) PR_GET_SECCOMP return  the  nonnegative
       values  described  above.  All other option values return 0 on success.
       On error, -1 is returned, and errno is set appropriately.

ERRORS
       EACCES option is PR_SET_SECCOMP and arg2  is  SECCOMP_MODE_FILTER,  but
              the  process  does  not have the CAP_SYS_ADMIN capability or has
              not set  the  no_new_privs  attribute  (see  the  discussion  of
              PR_SET_NO_NEW_PRIVS above).

       EACCES option is PR_SET_MM, and arg3 is PR_SET_MM_EXE_FILE, the file is
              not executable.

       EBADF  option is PR_SET_MM, arg3 is PR_SET_MM_EXE_FILE,  and  the  file
              descriptor passed in arg4 is not valid.

       EBUSY  option  is  PR_SET_MM,  arg3 is PR_SET_MM_EXE_FILE, and this the
              second attempt to change the /proc/pid/exe symbolic link,  which
              is prohibited.

       EFAULT arg2 is an invalid address.

       EFAULT option  is PR_SET_SECCOMP, arg2 is SECCOMP_MODE_FILTER, the sys‐
              tem was built with CONFIG_SECCOMP_FILTER, and arg3 is an invalid
              address.

       EINVAL The value of option is not recognized.

       EINVAL option  is  PR_MCE_KILL  or  PR_MCE_KILL_GET  or  PR_SET_MM, and
              unused prctl() arguments were not specified as zero.

       EINVAL arg2 is not valid value for this option.

       EINVAL option is PR_SET_SECCOMP or PR_GET_SECCOMP, and the  kernel  was
              not configured with CONFIG_SECCOMP.

       EINVAL option  is  PR_SET_SECCOMP, arg2 is SECCOMP_MODE_FILTER, and the
              kernel was not configured with CONFIG_SECCOMP_FILTER.

       EINVAL option is PR_SET_MM, and one of the following is true

              *  arg4 or arg5 is nonzero;

              *  arg3 is greater than TASK_SIZE (the limit on the size of  the
                 user address space for this architecture);

              *  arg2     is     PR_SET_MM_START_CODE,     PR_SET_MM_END_CODE,
                 PR_SET_MM_START_DATA,         PR_SET_MM_END_DATA,          or
                 PR_SET_MM_START_STACK, and the permissions of the correspond‐
                 ing memory area are not as required;

              *  arg2 is PR_SET_MM_START_BRK or  PR_SET_MM_BRK,  and  arg3  is
                 less  than  or equal to the end of the data segment or speci‐
                 fies a value that would cause the RLIMIT_DATA resource  limit
                 to be exceeded.

       EINVAL option  is PR_SET_PTRACER and arg2 is not 0, PR_SET_PTRACER_ANY,
              or the PID of an existing process.

       EINVAL option is PR_SET_PDEATHSIG and arg2 is not a valid  signal  num‐
              ber.

       EINVAL option  is PR_SET_DUMPABLE and arg2 is neither SUID_DUMP_DISABLE
              nor SUID_DUMP_USER.

       EINVAL option is PR_SET_TIMING and arg2 is not PR_TIMING_STATISTICAL.

       EINVAL option is PR_SET_NO_NEW_PRIVS and arg2 is  not  equal  to  1  or
              arg3, arg4, or arg5 is nonzero.

       EINVAL option  is  PR_GET_NO_NEW_PRIVS and arg2, arg3, arg4, or arg5 is
              nonzero.

       EINVAL option is PR_SET_THP_DISABLE and arg3, arg4, or arg5 is nonzero.

       EINVAL option is PR_GET_THP_DISABLE and arg2, arg3, arg4,  or  arg5  is
              nonzero.

       EINVAL option is PR_CAP_AMBIENT and an unused argument (arg4, arg5, or,
              in the case of PR_CAP_AMBIENT_CLEAR_ALL, arg3)  is  nonzero;  or
              arg2  has  an  invalid  value;  or arg2 is PR_CAP_AMBIENT_LOWER,
              PR_CAP_AMBIENT_RAISE, or PR_CAP_AMBIENT_IS_SET and arg3 does not
              specify a valid capability.

       ENODEV option  was  PR_SET_SPECULATION_CTRL  the kernel or CPU does not
              support the requested speculation misfeature.

       ENXIO  option was PR_MPX_ENABLE_MANAGEMENT or PR_MPX_DISABLE_MANAGEMENT
              and  the  kernel  or  the  CPU  does not support MPX management.
              Check that the kernel and processor have MPX support.

       ENXIO  option was PR_SET_SPECULATION_CTRL implies that the  control  of
              the  selected  speculation  misfeature  is  not  possible.   See
              PR_GET_SPECULATION_CTRL for the bit fields  to  determine  which
              option is available.

       EOPNOTSUPP
              option  is PR_SET_FP_MODE and arg2 has an invalid or unsupported
              value.

       EPERM  option is PR_SET_SECUREBITS, and the caller does  not  have  the
              CAP_SETPCAP  capability,  or  tried to unset a "locked" flag, or
              tried to set a flag whose corresponding locked flag was set (see
              capabilities(7)).

       EPERM  option  is  PR_SET_SPECULATION_CTRL  wherein the speculation was
              disabled with PR_SPEC_FORCE_DISABLE and caller tried  to  enable
              it again.

       EPERM  option      is     PR_SET_KEEPCAPS,     and     the     caller's
              SECBIT_KEEP_CAPS_LOCKED flag is set (see capabilities(7)).

       EPERM  option is PR_CAPBSET_DROP, and the  caller  does  not  have  the
              CAP_SETPCAP capability.

       EPERM  option   is   PR_SET_MM,  and  the  caller  does  not  have  the
              CAP_SYS_RESOURCE capability.

       EPERM  option is PR_CAP_AMBIENT and arg2 is  PR_CAP_AMBIENT_RAISE,  but
              either  the  capability  specified in arg3 is not present in the
              process's permitted and  inheritable  capability  sets,  or  the
              PR_CAP_AMBIENT_LOWER securebit has been set.

       ERANGE option   was   PR_SET_SPECULATION_CTRL   and   arg3  is  neither
              PR_SPEC_ENABLE, PR_SPEC_DISABLE, nor PR_SPEC_FORCE_DISABLE.

       EINVAL option was  PR_GET_SPECULATION_CTRL  or  PR_SET_SPECULATION_CTRL
              and unused arguments to prctl() are not 0.

VERSIONS
       The prctl() system call was introduced in Linux 2.1.57.

CONFORMING TO
       This  call  is  Linux-specific.   IRIX  has a prctl() system call (also
       introduced in Linux 2.1.44 as irix_prctl  on  the  MIPS  architecture),
       with prototype

           ptrdiff_t prctl(int option, int arg2, int arg3);

       and  options  to  get the maximum number of processes per user, get the
       maximum number of processors the calling  process  can  use,  find  out
       whether  a specified process is currently blocked, get or set the maxi‐
       mum stack size, and so on.

SEE ALSO
       signal(2), core(5)

COLOPHON
       This page is part of release 5.02 of the Linux  man-pages  project.   A
       description  of  the project, information about reporting bugs, and the
       latest    version    of    this    page,    can     be     found     at
       https://www.kernel.org/doc/man-pages/.



Linux                             2019-08-02                          PRCTL(2)
맨 페이지 내용의 저작권은 맨 페이지 작성자에게 있습니다.
RSS ATOM XHTML 5 CSS3