Re: [Linux-ima-devel] [PATCH v2 4/7] ima: measure and appraise kexec image and initramfs

[Petko Manolov <petkan@mip-labs.com>]

On 15-12-28 07:51:15, Mimi Zohar wrote:
> On Mon, 2015-12-28 at 10:08 +0800, Dave Young wrote:
> > On 12/25/15 at 09:45am, Mimi Zohar wrote:
> > > IMA calculates the file hash, in this case, based on the buffer
> > > contents.   The hash is calculated once and used for both measurement
> > > and appraisal.  If the file integrity appraisal fails (eg. hash
> > > comparison or signature failure), IMA prevents the kexec files from
> > > being used.
> > > 
> > 
> > Ok, thanks for the explanatioin. But I have another question, why do we
> > need a special hook for KEXEC? Shouldn't all files use same way to do the
> > measurement and appraisal?
> 
> "By all files" are you referring to all files read by the kernel or all
> files opened, executed or mmapped by the system?
> 
> Currently IMA allocates a page sized buffer, reads a file a page chunk
> at a time calculating the file hash as it does so, and then frees the
> buffer before returning to the caller.  This method of calculating the

I kind of wonder isn't it possible to optimize the file read?  If the file is 
relatively small (a few megabytes, for example) it will fit into any modern 
system's memory.  At least those that cares to run IMA, i mean.

Fetching file page by page is a slow process even though the BIO subsystem reads 
larger chunks off the real storage devices.  Has anyone done a benchmark test?


cheers,
Petko

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