152 строки
7.2 KiB
ReStructuredText
152 строки
7.2 KiB
ReStructuredText
Kernel Support for miscellaneous Binary Formats (binfmt_misc)
|
|
=============================================================
|
|
|
|
This Kernel feature allows you to invoke almost (for restrictions see below)
|
|
every program by simply typing its name in the shell.
|
|
This includes for example compiled Java(TM), Python or Emacs programs.
|
|
|
|
To achieve this you must tell binfmt_misc which interpreter has to be invoked
|
|
with which binary. Binfmt_misc recognises the binary-type by matching some bytes
|
|
at the beginning of the file with a magic byte sequence (masking out specified
|
|
bits) you have supplied. Binfmt_misc can also recognise a filename extension
|
|
aka ``.com`` or ``.exe``.
|
|
|
|
First you must mount binfmt_misc::
|
|
|
|
mount binfmt_misc -t binfmt_misc /proc/sys/fs/binfmt_misc
|
|
|
|
To actually register a new binary type, you have to set up a string looking like
|
|
``:name:type:offset:magic:mask:interpreter:flags`` (where you can choose the
|
|
``:`` upon your needs) and echo it to ``/proc/sys/fs/binfmt_misc/register``.
|
|
|
|
Here is what the fields mean:
|
|
|
|
- ``name``
|
|
is an identifier string. A new /proc file will be created with this
|
|
``name below /proc/sys/fs/binfmt_misc``; cannot contain slashes ``/`` for
|
|
obvious reasons.
|
|
- ``type``
|
|
is the type of recognition. Give ``M`` for magic and ``E`` for extension.
|
|
- ``offset``
|
|
is the offset of the magic/mask in the file, counted in bytes. This
|
|
defaults to 0 if you omit it (i.e. you write ``:name:type::magic...``).
|
|
Ignored when using filename extension matching.
|
|
- ``magic``
|
|
is the byte sequence binfmt_misc is matching for. The magic string
|
|
may contain hex-encoded characters like ``\x0a`` or ``\xA4``. Note that you
|
|
must escape any NUL bytes; parsing halts at the first one. In a shell
|
|
environment you might have to write ``\\x0a`` to prevent the shell from
|
|
eating your ``\``.
|
|
If you chose filename extension matching, this is the extension to be
|
|
recognised (without the ``.``, the ``\x0a`` specials are not allowed).
|
|
Extension matching is case sensitive, and slashes ``/`` are not allowed!
|
|
- ``mask``
|
|
is an (optional, defaults to all 0xff) mask. You can mask out some
|
|
bits from matching by supplying a string like magic and as long as magic.
|
|
The mask is anded with the byte sequence of the file. Note that you must
|
|
escape any NUL bytes; parsing halts at the first one. Ignored when using
|
|
filename extension matching.
|
|
- ``interpreter``
|
|
is the program that should be invoked with the binary as first
|
|
argument (specify the full path)
|
|
- ``flags``
|
|
is an optional field that controls several aspects of the invocation
|
|
of the interpreter. It is a string of capital letters, each controls a
|
|
certain aspect. The following flags are supported:
|
|
|
|
``P`` - preserve-argv[0]
|
|
Legacy behavior of binfmt_misc is to overwrite
|
|
the original argv[0] with the full path to the binary. When this
|
|
flag is included, binfmt_misc will add an argument to the argument
|
|
vector for this purpose, thus preserving the original ``argv[0]``.
|
|
e.g. If your interp is set to ``/bin/foo`` and you run ``blah``
|
|
(which is in ``/usr/local/bin``), then the kernel will execute
|
|
``/bin/foo`` with ``argv[]`` set to ``["/bin/foo", "/usr/local/bin/blah", "blah"]``. The interp has to be aware of this so it can
|
|
execute ``/usr/local/bin/blah``
|
|
with ``argv[]`` set to ``["blah"]``.
|
|
``O`` - open-binary
|
|
Legacy behavior of binfmt_misc is to pass the full path
|
|
of the binary to the interpreter as an argument. When this flag is
|
|
included, binfmt_misc will open the file for reading and pass its
|
|
descriptor as an argument, instead of the full path, thus allowing
|
|
the interpreter to execute non-readable binaries. This feature
|
|
should be used with care - the interpreter has to be trusted not to
|
|
emit the contents of the non-readable binary.
|
|
``C`` - credentials
|
|
Currently, the behavior of binfmt_misc is to calculate
|
|
the credentials and security token of the new process according to
|
|
the interpreter. When this flag is included, these attributes are
|
|
calculated according to the binary. It also implies the ``O`` flag.
|
|
This feature should be used with care as the interpreter
|
|
will run with root permissions when a setuid binary owned by root
|
|
is run with binfmt_misc.
|
|
``F`` - fix binary
|
|
The usual behaviour of binfmt_misc is to spawn the
|
|
binary lazily when the misc format file is invoked. However,
|
|
this doesn``t work very well in the face of mount namespaces and
|
|
changeroots, so the ``F`` mode opens the binary as soon as the
|
|
emulation is installed and uses the opened image to spawn the
|
|
emulator, meaning it is always available once installed,
|
|
regardless of how the environment changes.
|
|
|
|
|
|
There are some restrictions:
|
|
|
|
- the whole register string may not exceed 1920 characters
|
|
- the magic must reside in the first 128 bytes of the file, i.e.
|
|
offset+size(magic) has to be less than 128
|
|
- the interpreter string may not exceed 127 characters
|
|
|
|
To use binfmt_misc you have to mount it first. You can mount it with
|
|
``mount -t binfmt_misc none /proc/sys/fs/binfmt_misc`` command, or you can add
|
|
a line ``none /proc/sys/fs/binfmt_misc binfmt_misc defaults 0 0`` to your
|
|
``/etc/fstab`` so it auto mounts on boot.
|
|
|
|
You may want to add the binary formats in one of your ``/etc/rc`` scripts during
|
|
boot-up. Read the manual of your init program to figure out how to do this
|
|
right.
|
|
|
|
Think about the order of adding entries! Later added entries are matched first!
|
|
|
|
|
|
A few examples (assumed you are in ``/proc/sys/fs/binfmt_misc``):
|
|
|
|
- enable support for em86 (like binfmt_em86, for Alpha AXP only)::
|
|
|
|
echo ':i386:M::\x7fELF\x01\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x02\x00\x03:\xff\xff\xff\xff\xff\xfe\xfe\xff\xff\xff\xff\xff\xff\xff\xff\xff\xfb\xff\xff:/bin/em86:' > register
|
|
echo ':i486:M::\x7fELF\x01\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x02\x00\x06:\xff\xff\xff\xff\xff\xfe\xfe\xff\xff\xff\xff\xff\xff\xff\xff\xff\xfb\xff\xff:/bin/em86:' > register
|
|
|
|
- enable support for packed DOS applications (pre-configured dosemu hdimages)::
|
|
|
|
echo ':DEXE:M::\x0eDEX::/usr/bin/dosexec:' > register
|
|
|
|
- enable support for Windows executables using wine::
|
|
|
|
echo ':DOSWin:M::MZ::/usr/local/bin/wine:' > register
|
|
|
|
For java support see Documentation/admin-guide/java.rst
|
|
|
|
|
|
You can enable/disable binfmt_misc or one binary type by echoing 0 (to disable)
|
|
or 1 (to enable) to ``/proc/sys/fs/binfmt_misc/status`` or
|
|
``/proc/.../the_name``.
|
|
Catting the file tells you the current status of ``binfmt_misc/the_entry``.
|
|
|
|
You can remove one entry or all entries by echoing -1 to ``/proc/.../the_name``
|
|
or ``/proc/sys/fs/binfmt_misc/status``.
|
|
|
|
|
|
Hints
|
|
-----
|
|
|
|
If you want to pass special arguments to your interpreter, you can
|
|
write a wrapper script for it.
|
|
See :doc:`Documentation/admin-guide/java.rst <./java>` for an example.
|
|
|
|
Your interpreter should NOT look in the PATH for the filename; the kernel
|
|
passes it the full filename (or the file descriptor) to use. Using ``$PATH`` can
|
|
cause unexpected behaviour and can be a security hazard.
|
|
|
|
|
|
Richard Günther <rguenth@tat.physik.uni-tuebingen.de>
|