Opcode(3) 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.
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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Opcode(3) Opcode(3)
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.
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 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'
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Opcode(3) Opcode(3)
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
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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Opcode(3) Opcode(3)
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.
: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
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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 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
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Opcode(3) Opcode(3)
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 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
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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