Opcode(3)
Opcode(3) Perl Programmers Reference Guide 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, 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 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 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.
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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 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 opset 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
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 340 for
perl5.002).
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.
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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.
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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 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
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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
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 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.
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: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 filehandle (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
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
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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 reasonable 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
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
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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 possibly as dangerous?
:subprocess
backtick system
fork
wait waitpid
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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
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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SEE ALSO
ops(3) -- perl pragma interface to Opcode module.
Safe(3) -- Opcode and namespace limited execution
compartments
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 <Tim.Bunce@ig.co.uk>.
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Opcode(3) Perl Programmers Reference Guide Opcode(3)
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