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Subject: Re: [PATCH 0/3] fs: reduce export usage of kerne_read*() calls
From:   Mimi Zohar <zohar@linux.ibm.com>
To:     Christoph Hellwig <hch@infradead.org>,
        Luis Chamberlain <mcgrof@kernel.org>
Cc:     viro@zeniv.linux.org.uk, gregkh@linuxfoundation.org,
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Date:   Mon, 18 May 2020 08:37:42 -0400
In-Reply-To: <20200518062255.GB15641@infradead.org>
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         <20200513181736.GA24342@infradead.org>
         <20200515212933.GD11244@42.do-not-panic.com>
         <20200518062255.GB15641@infradead.org>
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Hi Christoph,

On Sun, 2020-05-17 at 23:22 -0700, Christoph Hellwig wrote:
> On Fri, May 15, 2020 at 09:29:33PM +0000, Luis Chamberlain wrote:
> > On Wed, May 13, 2020 at 11:17:36AM -0700, Christoph Hellwig wrote:
> > > Can you also move kernel_read_* out of fs.h?  That header gets pulled
> > > in just about everywhere and doesn't really need function not related
> > > to the general fs interface.
> > 
> > Sure, where should I dump these?
> 
> Maybe a new linux/kernel_read_file.h?  Bonus points for a small top
> of the file comment explaining the point of the interface, which I
> still don't get :)

Instead of rolling your own method of having the kernel read a file,
which requires call specific security hooks, this interface provides a
single generic set of pre and post security hooks.  The
kernel_read_file_id enumeration permits the security hook to
differentiate between callers.

To comply with secure and trusted boot concepts, a file cannot be
accessible to the caller until after it has been measured and/or the
integrity (hash/signature) appraised.

In some cases, the file was previously read twice, first to measure
and/or appraise the file and then read again into a buffer for
use.  This interface reads the file into a buffer once, calls the
generic post security hook, before providing the buffer to the caller.
 (Note using firmware pre-allocated memory might be an issue.)

Partial reading firmware will result in needing to pre-read the entire
file, most likely on the security pre hook.

Mimi