Adding upstream version 5.10.209.upstream/5.10.209upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 151 insertions, 0 deletions

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+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>