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

[Mimi Zohar <zohar@linux.vnet.ibm.com>]

On Mon, 2015-12-28 at 16:59 +0200, Petko Manolov wrote:
> On 15-12-28 09:42:22, Mimi Zohar wrote:
> > On Mon, 2015-12-28 at 16:29 +0200, Petko Manolov wrote:
> > > 
> > > 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?
> > 
> > Dmitry recently added asynchronous hash (ahash) support, which allows HW 
> > crypto acceleration, for calculating the file hash.
> 
> This is nice.  However, i was referring to reading a file page by page vs larger 
> (a couple of megabytes) chunks.  Is this also covered by the ahash support?

Yes,  basically it attempts to allocate a buffer for the entire file.
On failure, ahash attempts to allocate two buffers larger than
PAGE_SIZE, but falls back to using just PAGE_SIZE.  Refer to
ima_alloc_pages() for a full description.

When two buffers are allocated, while waiting for one hash to complete,
the subsequent file read is read into the other buffer.

Mimi


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