opcode(3)

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, exe
cuted. The internal format is based on many distinct
opcodes.

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

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 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 dam
ages 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 excla
mation 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 ver
ify_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 pro
cess 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 opera
tors & (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 eqiv
$yes = opset_can($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; 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 qr; list lslice splice push pop shift unshift reverse; cond_expr flip flop andassign orassign and or xor; warn die lineseq nextstate scope enter leave set; state; rv2cv anoncode prototype; entersub leavesub leavesublv return method; method_named -- 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 imple
ment a resource attack (e.g., consume all available
memory).

concat repeat join range

anonlist anonhash; Note that despite the existance of this optag a mem
ory 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 assump
tion 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

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 ob

jects (reblessing)

pushre regcmaybe regcreset regcomp subst subst

cont

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

custom -- where should this go
: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 threadsv
:default: A handy tag name for a reasonable default set of ops. (The current ops allowed are unstable while develop
ment continues. It will change.)

:base_core :base_mem :base_loop :base_io

:base_orig :base_thread; 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 fte; owned fteread
ftewrite ftfile ftis ftlink ftmtime ftpipe ftrex; ec 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 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
:filesys_write: link unlink rename symlink truncate; mkdir rmdir; utime chmod chown; fcntl -- not strictly filesys related, but possi; bly 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 get; sockname; 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 ini; tial compile
require dofile; caller -- get info about calling environment and; args; reset; dbstate -- perl -d version of nextstate(ment) op; code
: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

AUTHORS

Originally designed and implemented by Malcolm Beattie,
mbeattie@sable.ox.ac.uk as part of Safe version 1.

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

docs.sk

comprehensive documentation repository

In section

See also