IRIX Base Documentation 2001 May/SGI IRIX Base Documentation 2001 May.iso/usr/share/catman/p_man/cat3/perl5/Opcode.z/Opcode

Text File | 1998-10-30 | 19.2 KB | 661 lines

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     Opcode - Disable named opcodes when compiling perl code

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       use Opcode;


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     Perl code is always compiled into an internal format before execution.

     Evaluating perl code (e.g. via "eval" or "do 'file'") causes the code to
     be compiled into an internal format and then, provided there was no error
     in the compilation, executed.  The internal format is based on many
     distinct _o_p_c_o_d_e_s.

     By default no opmask is in effect and any code can be compiled.

     The Opcode module allow you to define an _o_p_e_r_a_t_o_r _m_a_s_k to be in effect
     when perl _n_e_x_t compiles any code.  Attempting to compile code which
     contains a masked opcode will cause the compilation to fail with an
     error. The code will not be executed.

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     The Opcode module is not usually used directly. See the ops pragma and
     Safe modules for more typical uses.

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     The authors make nnnnoooo wwwwaaaarrrrrrrraaaannnnttttyyyy, implied or otherwise, about the suitability
     of this software for safety or security purposes.

     The authors shall not in any case be liable for special, incidental,
     consequential, indirect or other similar damages arising from the use of
     this software.

     Your mileage will vary. If in any doubt ddddoooo nnnnooootttt uuuusssseeee iiiitttt.

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     The canonical list of operator names is the contents of the array op_name
     defined and initialised in file _o_p_c_o_d_e._h of the Perl source distribution
     (and installed into the perl library).

     Each operator has both a terse name (its opname) and a more verbose or
     recognisable descriptive name. The opdesc function can be used to return
     a list of descriptions for a list of operators.

     Many of the functions and methods listed below take a list of operators
     as parameters. Most operator lists can be made up of several types of
     element. Each element can be one of

     an operator name (opname)
             Operator names are typically small lowercase words like
             enterloop, leaveloop, last, next, redo etc. Sometimes they are



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             rather cryptic like gv2cv, i_ncmp and ftsvtx.

     an operator tag name (optag)
             Operator tags can be used to refer to groups (or sets) of
             operators.  Tag names always being with a colon. The Opcode
             module defines several optags and the user can define others
             using the define_optag function.

     a negated opname or optag
             An opname or optag can be prefixed with an exclamation mark,
             e.g., !mkdir.  Negating an opname or optag means remove the
             corresponding ops from the accumulated set of ops at that point.

     an operator set (opset)
             An _o_p_s_e_t as a binary string of approximately 43 bytes which holds
             a set or zero or more operators.

             The opset and opset_to_ops functions can be used to convert from
             a list of operators to an opset and _v_i_c_e _v_e_r_s_a.

             Wherever a list of operators can be given you can use one or more
             opsets.  See also Manipulating Opsets below.

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     The Opcode package contains functions for manipulating operator names
     tags and sets. All are available for export by the package.

     opcodes In a scalar context opcodes returns the number of opcodes in this
             version of perl (around 340 for perl5.002).

             In a list context it returns a list of all the operator names.
             (Not yet implemented, use @names = _o_p_s_e_t__t_o__o_p_s(full_opset).)

     opset (OP, ...)
             Returns an opset containing the listed operators.

     opset_to_ops (OPSET)
             Returns a list of operator names corresponding to those operators
             in the set.

     opset_to_hex (OPSET)
             Returns a string representation of an opset. Can be handy for
             debugging.

     full_opset
             Returns an opset which includes all operators.

     empty_opset
             Returns an opset which contains no operators.






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     invert_opset (OPSET)
             Returns an opset which is the inverse set of the one supplied.

     verify_opset (OPSET, ...)
             Returns true if the supplied opset looks like a valid opset (is
             the right length etc) otherwise it returns false. If an optional
             second parameter is true then verify_opset will croak on an
             invalid opset instead of returning false.

             Most of the other Opcode functions call verify_opset
             automatically and will croak if given an invalid opset.

     define_optag (OPTAG, OPSET)
             Define OPTAG as a symbolic name for OPSET. Optag names always
             start with a colon :.

             The optag name used must not be defined already (define_optag
             will croak if it is already defined). Optag names are global to
             the perl process and optag definitions cannot be altered or
             deleted once defined.

             It is strongly recommended that applications using Opcode should
             use a leading capital letter on their tag names since lowercase
             names are reserved for use by the Opcode module. If using Opcode
             within a module you should prefix your tags names with the name
             of your module to ensure uniqueness and thus avoid clashes with
             other modules.

     opmask_add (OPSET)
             Adds the supplied opset to the current opmask. Note that there is
             currently _n_o mechanism for unmasking ops once they have been
             masked.  This is intentional.

     opmask  Returns an opset corresponding to the current opmask.

     opdesc (OP, ...)
             This takes a list of operator names and returns the corresponding
             list of operator descriptions.

     opdump (PAT)
             Dumps to STDOUT a two column list of op names and op
             descriptions.  If an optional pattern is given then only lines
             which match the (case insensitive) pattern will be output.

             It's designed to be used as a handy command line utility:

                     perl -MOpcode=opdump -e opdump
                     perl -MOpcode=opdump -e 'opdump Eval'







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     Opsets may be manipulated using the perl bit vector operators & (and), |
     (or), ^ (xor) and ~ (negate/invert).

     However you should never rely on the numerical position of any opcode
     within the opset. In other words both sides of a bit vector operator
     should be opsets returned from Opcode functions.

     Also, since the number of opcodes in your current version of perl might
     not be an exact multiple of eight, there may be unused bits in the last
     byte of an upset. This should not cause any problems (Opcode functions
     ignore those extra bits) but it does mean that using the ~ operator will
     typically not produce the same 'physical' opset 'string' as the
     invert_opset function.

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         $bool = opset_eq($opset1, $opset2)  true if opsets are logically eqiv

         $yes = opset_can($opset, @ops)      true if $opset has all @ops set

         @diff = opset_diff($opset1, $opset2) => ('foo', '!bar', ...)


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     :base_core

              null stub scalar pushmark wantarray const defined undef

              rv2sv sassign

              rv2av aassign aelem aelemfast aslice av2arylen

              rv2hv helem hslice each values keys exists delete

              preinc i_preinc predec i_predec postinc i_postinc postdec i_postdec
              int hex oct abs pow multiply i_multiply divide i_divide
              modulo i_modulo add i_add subtract i_subtract

              left_shift right_shift bit_and bit_xor bit_or negate i_negate
              not complement

              lt i_lt gt i_gt le i_le ge i_ge eq i_eq ne i_ne ncmp i_ncmp
              slt sgt sle sge seq sne scmp

              substr vec stringify study pos length index rindex ord chr

              ucfirst lcfirst uc lc quotemeta trans chop schop chomp schomp

              match split

              list lslice splice push pop shift unshift reverse




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              cond_expr flip flop andassign orassign and or xor

              warn die lineseq nextstate unstack scope enter leave

              rv2cv anoncode prototype

              entersub leavesub return method -- XXX loops via recursion?

              leaveeval -- needed for Safe to operate, is safe without entereval


     :base_mem
          These memory related ops are not included in :base_core because they
          can easily be used to implement a resource attack (e.g., consume all
          available memory).

              concat repeat join range

              anonlist anonhash

          Note that despite the existance of this optag a memory resource
          attack may still be possible using only :base_core ops.

          Disabling these ops is a _v_e_r_y heavy handed way to attempt to prevent
          a memory resource attack. It's probable that a specific memory limit
          mechanism will be added to perl in the near future.

     :base_loop
          These loop ops are not included in :base_core because they can
          easily be used to implement a resource attack (e.g., consume all
          available CPU time).

              grepstart grepwhile
              mapstart mapwhile
              enteriter iter
              enterloop leaveloop
              last next redo
              goto


     :base_io
          These ops enable _f_i_l_e_h_a_n_d_l_e (rather than filename) based input and
          output. These are safe on the assumption that only pre-existing
          filehandles are available for use.  To create new filehandles other
          ops such as open would need to be enabled.

              readline rcatline getc read

              formline enterwrite leavewrite

              print sysread syswrite send recv




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              eof tell seek sysseek

              readdir telldir seekdir rewinddir


     :base_orig
          These are a hotchpotch of opcodes still waiting to be considered

              gvsv gv gelem

              padsv padav padhv padany

              rv2gv refgen srefgen ref

              bless -- could be used to change ownership of objects (reblessing)

              pushre regcmaybe regcomp subst substcont

              sprintf prtf -- can core dump

              crypt

              tie untie

              dbmopen dbmclose
              sselect select
              pipe_op sockpair

              getppid getpgrp setpgrp getpriority setpriority localtime gmtime

              entertry leavetry -- can be used to 'hide' fatal errors


     :base_math
          These ops are not included in :base_core because of the risk of them
          being used to generate floating point exceptions (which would have
          to be caught using a $SIG{FPE} handler).

              atan2 sin cos exp log sqrt

          These ops are not included in :base_core because they have an effect
          beyond the scope of the compartment.

              rand srand


     :default
          A handy tag name for a _r_e_a_s_o_n_a_b_l_e default set of ops.  (The current
          ops allowed are unstable while development continues. It will
          change.)

              :base_core :base_mem :base_loop :base_io :base_orig



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          If safety matters to you (and why else would you be using the Opcode
          module?)  then you should not rely on the definition of this, or
          indeed any other, optag!

     :filesys_read

              stat lstat readlink

              ftatime ftblk ftchr ftctime ftdir fteexec fteowned fteread
              ftewrite ftfile ftis ftlink ftmtime ftpipe ftrexec ftrowned
              ftrread ftsgid ftsize ftsock ftsuid fttty ftzero ftrwrite ftsvtx

              fttext ftbinary

              fileno


     :sys_db

              ghbyname ghbyaddr ghostent shostent ehostent      -- hosts
              gnbyname gnbyaddr gnetent snetent enetent         -- networks
              gpbyname gpbynumber gprotoent sprotoent eprotoent -- protocols
              gsbyname gsbyport gservent sservent eservent      -- services

              gpwnam gpwuid gpwent spwent epwent getlogin       -- users
              ggrnam ggrgid ggrent sgrent egrent                -- groups


     :browse
          A handy tag name for a _r_e_a_s_o_n_a_b_l_e default set of ops beyond the
          :default optag.  Like :default (and indeed all the other optags) its
          current definition is unstable while development continues. It will
          change.

          The :browse tag represents the next step beyond :default. It it a
          superset of the :default ops and adds :filesys_read the :sys_db.
          The intent being that scripts can access more (possibly sensitive)
          information about your system but not be able to change it.

              :default :filesys_read :sys_db


     :filesys_open

              sysopen open close
              umask binmode

              open_dir closedir -- other dir ops are in :base_io







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     :filesys_write

              link unlink rename symlink truncate

              mkdir rmdir

              utime chmod chown

              fcntl -- not strictly filesys related, but possibly as dangerous?


     :subprocess

              backtick system

              fork

              wait waitpid

              glob -- access to Cshell via <`rm *`>


     :ownprocess

              exec exit kill

              time tms -- could be used for timing attacks (paranoid?)


     :others
          This tag holds groups of assorted specialist opcodes that don't
          warrant having optags defined for them.

          SystemV Interprocess Communications:

              msgctl msgget msgrcv msgsnd

              semctl semget semop

              shmctl shmget shmread shmwrite


     :still_to_be_decided

              chdir
              flock ioctl

              socket getpeername ssockopt
              bind connect listen accept shutdown gsockopt getsockname






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              sleep alarm -- changes global timer state and signal handling
              sort -- assorted problems including core dumps
              tied -- can be used to access object implementing a tie
              pack unpack -- can be used to create/use memory pointers

              entereval -- can be used to hide code from initial compile
              require dofile

              caller -- get info about calling environment and args

              reset

              dbstate -- perl -d version of nextstate(ment) opcode


     :dangerous
          This tag is simply a bucket for opcodes that are unlikely to be used
          via a tag name but need to be tagged for completness and
          documentation.

              syscall dump chroot


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     _o_p_s(3) -- perl pragma interface to Opcode module.

     _S_a_f_e(3) -- Opcode and namespace limited execution compartments

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     Originally designed and implemented by Malcolm Beattie,
     [e-mail] as part of Safe version 1.

     Split out from Safe module version 1, named opcode tags and other changes
     added by Tim Bunce <_T_i_m._B_u_n_c_e@_i_g._c_o._u_k>.





















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