man > Opcode(3perl)

NAME
    Opcode - Disable named opcodes when compiling perl code

SYNOPSIS
      use Opcode;

DESCRIPTION
    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 *opcodes*.

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

    The Opcode module allow you to define an *operator mask* to be in effect when perl *next*
    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.

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

WARNING
    The Opcode module does not implement an effective sandbox for evaluating untrusted code with the
    perl interpreter.

    Bugs in the perl interpreter that could be abused to bypass Opcode restrictions are not treated
    as vulnerabilities. See perlsecpolicy for additional information.

    The authors make no warranty, 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 do not use it.

Operator Names and Operator Lists
    The canonical list of operator names is the contents of the array PL_op_name defined and
    initialised in file opcode.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 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
            begin 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 *opset* as a binary string of approximately 44 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 *vice versa*.

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

Opcode Functions
    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 350 for perl-5.7.0).

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

    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 *no*
            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'

Manipulating Opsets
    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.

TO DO (maybe)
        $bool = opset_eq($opset1, $opset2)  true if opsets are logically
                                            equivalent
        $yes = opset_can($opset, @ops)      true if $opset has all @ops set

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

Predefined Opcode Tags
    :base_core
             null stub scalar pushmark wantarray const defined undef

             rv2sv sassign padsv_store

             rv2av aassign aelem aelemfast aelemfast_lex aslice kvaslice
             av2arylen aelemfastlex_store

             rv2hv helem hslice kvhslice each values keys exists delete
             aeach akeys avalues multideref argelem argdefelem argcheck

             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 nbit_and
             nbit_xor nbit_or sbit_and sbit_xor sbit_or negate i_negate not
             complement ncomplement scomplement

             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
             isa

             substr vec stringify study pos length index rindex ord chr

             ucfirst lcfirst uc lc fc quotemeta trans transr chop schop
             chomp schomp

             match split qr

             list lslice splice push pop shift unshift reverse

             cond_expr flip flop andassign orassign dorassign and or dor xor
             helemexistsor

             warn die lineseq nextstate scope enter leave

             rv2cv anoncode prototype coreargs avhvswitch anonconst
             emptyavhv

             entersub leavesub leavesublv return method method_named
             method_super method_redir method_redir_super
              -- XXX loops via recursion?

             cmpchain_and cmpchain_dup

             is_bool
             is_weak weaken unweaken

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

             methstart initfield

    :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 multiconcat repeat join range

             anonlist anonhash

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

         Disabling these ops is a *very* 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 unstack
             last next redo
             goto

    :base_io
         These ops enable *filehandle* (rather than filename) based input and output. These are safe
         on the assumption that only pre-existing filehandles are available for use. Usually, to
         create new filehandles other ops such as open would need to be enabled, if you don't take
         into account the magical open of ARGV.

             readline rcatline getc read

             formline enterwrite leavewrite

             print say sysread syswrite send recv

             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 padcv padany padrange introcv clonecv

             once

             rv2gv refgen srefgen ref refassign lvref lvrefslice lvavref
             blessed refaddr reftype

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

              regcmaybe regcreset 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
             entertrycatch poptry catch leavetrycatch -- similar

             entergiven leavegiven
             enterwhen leavewhen
             break continue
             smartmatch

             pushdefer

             custom -- where should this go

             ceil floor

             is_tainted

    :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

    :base_thread
         These ops are related to multi-threading.

             lock

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

             :base_core :base_mem :base_loop :base_orig :base_thread

         This list used to contain :base_io prior to Opcode 1.07.

         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 *reasonable* 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 is 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

    :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

    :load
         This tag holds opcodes related to loading modules and getting information about calling
         environment and args.

             require dofile
             caller runcv

    :still_to_be_decided
             chdir
             flock ioctl

             socket getpeername ssockopt
             bind connect listen accept shutdown gsockopt getsockname

             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

             hintseval -- constant op holding eval hints

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

             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 completeness and documentation.

             syscall dump chroot

SEE ALSO
    ops -- perl pragma interface to Opcode module.

    Safe -- Opcode and namespace limited execution compartments

AUTHORS
    Originally designed and implemented by Malcolm Beattie, mbeattie AT sable.uk as part of Safe
    version 1.

    Split out from Safe module version 1, named opcode tags and other changes added by Tim Bunce.