Re: [PATCH 0/3] fs: reduce export usage of kerne_read*() calls

From: Luis Chamberlain <mcgrof@kernel.org>
To: Kees Cook <keescook@chromium.org>
Cc: Mimi Zohar <zohar@linux.ibm.com>,
	Christoph Hellwig <hch@infradead.org>,
	viro@zeniv.linux.org.uk, gregkh@linuxfoundation.org,
	rafael@kernel.org, ebiederm@xmission.com, jeyu@kernel.org,
	jmorris@namei.org, paul@paul-moore.com,
	stephen.smalley.work@gmail.com, eparis@parisplace.org,
	nayna@linux.ibm.com, scott.branden@broadcom.com,
	dan.carpenter@oracle.com, skhan@linuxfoundation.org,
	geert@linux-m68k.org, tglx@linutronix.de, bauerman@linux.ibm.com,
	dhowells@redhat.com, linux-integrity@vger.kernel.org,
	linux-fsdevel@vger.kernel.org, kexec@lists.infradead.org,
	linux-security-module@vger.kernel.org, selinux@vger.kernel.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH 0/3] fs: reduce export usage of kerne_read*() calls
Date: Wed, 29 Jul 2020 01:20:39 +0000	[thread overview]
Message-ID: <20200729012039.GN4332@42.do-not-panic.com> (raw)
In-Reply-To: <202005180820.46CEF3C2@keescook>

On Mon, May 18, 2020 at 08:21:08AM -0700, Kees Cook wrote:
> On Mon, May 18, 2020 at 08:37:42AM -0400, Mimi Zohar wrote:
> > 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.
> 
> Well described! :)

Since you're moving all this stuff, it woudl be good if you can add this
as part of new kdoc as well.

  Luis