Re: [PATCH 1/4] module: add syscall to load module from fd

[Michael Kerrisk (man-pages)]

On Wed, Jan 9, 2013 at 6:29 PM, Lucas De Marchi
<lucas.demarchi@xxxxxxxxxxxxxx> wrote:
> On Sun, Jan 6, 2013 at 4:59 PM, Michael Kerrisk (man-pages)
> <mtk.manpages@xxxxxxxxx> wrote:
>> Hi Rusty, (and Lucas, and Kees)
>>
>> On Thu, Jan 3, 2013 at 1:12 AM, Rusty Russell <rusty@xxxxxxxxxxxxxxx> wrote:
>>> Michael Kerrisk <mtk.manpages@xxxxxxxxx> writes:
>>>> Hi Rusty,
>>>
>>> Hi Michael,
>>>
>>>> The description here is rather thin. Could you supply a sentence or
>>>> two for each of MODULE_INIT_IGNORE_MODVERSIONS and
>>>> MODULE_INIT_IGNORE_VERMAGIC that would be suitable for the manual
>>>> page?
>>>>
>>>> Thanks,
>>>
>>> There are one or two safety checks built into a module, which are
>>> checked to match the kernel on module load.  The first is a "vermagic"
>>> string containing the kernel version number and prominent features (such
>>> as CPU type).  If the module was built with CONFIG_MODVERSIONS set, a
>>> version hash is recorded for each symbol the module uses based on the
>>> types it refers to: in this case, the kernel version number within the
>>> "vermagic" string is ignored, as the symbol version hashes are assumed
>>> to be sufficiently reliable.
>>>
>>> Using the MODULE_INIT_IGNORE_VERMAGIC flag indicates that the vermagic
>>> is to be ignored, and the MODULE_INIT_IGNORE_MODVERSIONS flag indicates
>>> that the version hashes are to be ignored.  If the kernel is built to
>>> permit such forced loading (ie. CONFIG_MODULE_FORCE_LOAD is set) then
>>> loading will continue, otherwise it will fail with ENOEXEC as expected
>>> for malformed modules.
>>>
>>> Hope that is more usable?
>>
>> Yes, that helps. I did some reworking of that text. Hopefully, I did
>> not introduce any errors.
>>
>> Below is the text that is proposed to document finit_module() in the
>> man pages. I'd appreciate any review (Kees, Lucas, Rusty?)
>>
>> Thanks,
>>
>> Michael
>>
>>    finit_module()
>>        The finit_module() system call is like init_module(), but reads
>>        the module to be loaded from the file  descriptor  fd.   It  is
>>        useful  when  the authenticity of a kernel module can be deterâ
>>        mined from its location in the file system; in cases where that
>>        is  possible,  the  overhead  of using cryptographically signed
>>        modules to determine  the  authenticity  of  a  module  can  be
>>        avoided.  The param_values argument is as for init_module().
>>
>>        The  flags  argument  modifies the operation of finit_module().
>>        It is a bit mask value created by ORing together zero  or  more
>>        of the following flags:
>>
>>        MODULE_INIT_IGNORE_MODVERSIONS
>>               Ignore symbol version hashes.
>>
>>        MODULE_INIT_IGNORE_VERMAGIC
>>               Ignore kernel version magic.
>>
>>        There are some safety checks built into a module to ensure that
>>        it matches the kernel against which it is loaded.  These checks
>>        are  recorded  when  the  module is built and verified when the
>>        module is loaded.   First,  the  module  records  a  "vermagic"
>>        string  containing the kernel version number and prominent feaâ
>>        tures (such as the CPU type).  Second, if the module was  built
>>        with  the  CONFIG_MODVERSIONS  configuration  option enabled, a
>>        version hash is recorded for each symbol the module uses.  This
>>        hash  is  based  on the types of the arguments and return value
>>        for the function named by the symbol.  In this case, the kernel
>>        version  number within the "vermagic" string is ignored, as the
>>        symbol version hashes are assumed to be sufficiently reliable.
>>
>>        Using the MODULE_INIT_IGNORE_VERMAGIC flag indicates  that  the
>>        "vermagic"   string   is   to   be   ignored,   and   the  MODâ
>>        ULE_INIT_IGNORE_MODVERSIONS flag indicates that the symbol verâ
>>        sion  hashes are to be ignored.  If the kernel is built to perâ
>>        mit  forced  loading   (i.e.,   configured   with   CONFIG_MODâ
>>        ULE_FORCE_LOAD),  then loading will continue, otherwise it will
>>        fail with ENOEXEC as expected for malformed modules.
>> ...
>>    ERRORS
>> ...
>>        The following errors may additionally occur for finit_module():
>>
>>        EBADF  The file referred to by fd is not opened for reading.
>>
>>        EFBIG  The file referred to by fd is too large.
>>
>>        EINVAL flags is invalid.
>>
>>        ENOEXEC
>>               fd does not refer to an open file.
>>
>>
>
>
> Looks good to me.

Thanks for looking it over, Lucas.

Cheers,

Michael

-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Author of "The Linux Programming Interface"; http://man7.org/tlpi/
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