Opcode - Disable named opcodes when compiling perl code
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.
The Opcode module is not usually used directly. See the ops pragma and Safe modules for more typical uses.
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.
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
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.
The Opcode package contains functions for manipulating operator names tags and sets. All are available for export by the package.
In a list context it returns a list of all the operator names. (Not yet implemented, use
Most of the other Opcode functions call verify_opset automatically and will croak if given an invalid opset.
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.
It's designed to be used as a handy command line utility:
perl -MOpcode=opdump -e opdump perl -MOpcode=opdump -e 'opdump Eval'
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.
$bool = opset_eq($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', ...)
null stub scalar pushmark wantarray const defined undef
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 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
concat repeat join range
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.
grepstart grepwhile mapstart mapwhile enteriter iter enterloop leaveloop last next redo goto
readline rcatline getc read
formline enterwrite leavewrite
print sysread syswrite send recv
eof tell seek sysseek
readdir telldir seekdir rewinddir
gvsv gv gelem
padsv padav padhv padany
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
dbmopen dbmclose sselect select pipe_op sockpair
getppid getpgrp setpgrp getpriority setpriority localtime gmtime
entertry leavetry -- can be used to 'hide' fatal errors
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.
: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!
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
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
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
sysopen open close umask binmode
open_dir closedir -- other dir ops are in :base_io
link unlink rename symlink truncate
utime chmod chown
fcntl -- not strictly filesys related, but possibly as dangerous?
glob -- access to Cshell via <`rm *`>
exec exit kill
time tms -- could be used for timing attacks (paranoid?)
SystemV Interprocess Communications:
msgctl msgget msgrcv msgsnd
semctl semget semop
shmctl shmget shmread shmwrite
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
dbstate -- perl -d version of nextstate(ment) opcode
syscall dump chroot
ops(3) -- perl pragma
interface to Opcode module.
Safe(3) -- Opcode and
namespace limited execution compartments
Originally designed and implemented by Malcolm Beattie, firstname.lastname@example.org as part of Safe version 1.
Split out from Safe module version 1, named opcode tags and other changes added by Tim Bunce.
If rather than formatting bugs, you encounter substantive content errors in these documents, such as mistakes in the explanations or code, please use the perlbug utility included with the Perl distribution.