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SubjectRe: [PATCH 1/4] module: add syscall to load module from fd
On Sun, Jan 6, 2013 at 4:59 PM, Michael Kerrisk (man-pages)
<mtk.manpages@gmail.com> wrote:
> Hi Rusty, (and Lucas, and Kees)
>
> On Thu, Jan 3, 2013 at 1:12 AM, Rusty Russell <rusty@rustcorp.com.au> wrote:
>> Michael Kerrisk <mtk.manpages@gmail.com> 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 deter‐
> 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 fea‐
> 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 MOD‐
> ULE_INIT_IGNORE_MODVERSIONS flag indicates that the symbol ver‐
> sion hashes are to be ignored. If the kernel is built to per‐
> mit forced loading (i.e., configured with CONFIG_MOD‐
> 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.


regards,
Lucas De Marchi
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