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 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 eqiv
$yes = opset_can($opset, @ops) true if $opset has all @ops set
@diff = opset_diff($opset1, $opset2) => ('foo', '!bar', ...)
- :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 aeach akeys avalues
boolkeys reach rvalues rkeys
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 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
warn die lineseq nextstate scope enter leave
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 implement a resource attack (e.g.,
consume all available memory).
concat 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 padany
once
rv2gv refgen srefgen ref
bless -- could be used to change ownership of objects (reblessing)
pushre 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
entergiven leavegiven
enterwhen leavewhen
break continue
smartmatch
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
- :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 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
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
- :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@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.