linux-kernel - Re: [PATCH 2/3] binfmt_elf: Verify signature of signed elf binary

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Message-ID: <20130116182804.GF29845@redhat.com>
Date:	Wed, 16 Jan 2013 13:28:04 -0500
From:	Vivek Goyal <vgoyal@...hat.com>
To:	Mimi Zohar <zohar@...ux.vnet.ibm.com>
Cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	linux-kernel@...r.kernel.org, pjones@...hat.com, hpa@...or.com,
	dhowells@...hat.com, jwboyer@...hat.com,
	Dmitry Kasatkin <dmitry.kasatkin@...el.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-security-module@...r.kernel.org
Subject: Re: [PATCH 2/3] binfmt_elf: Verify signature of signed elf binary

On Wed, Jan 16, 2013 at 01:08:35PM -0500, Mimi Zohar wrote:
> On Wed, 2013-01-16 at 11:34 -0500, Vivek Goyal wrote:
> 
> > I read the comment in ima_bprm_check() being called from security_bprm_check(). 
> > It says that files already open for write can't executed and files already
> > open for exec can't be open for writes. That's fine. 
> > 
> > I was worried about anonymous pages being modified on swap and then
> > faulted back in. It is not necessarily signature verification but making
> > sure signed processes memory is not modified later by any unsigned process
> > in anyway. And that includes disabling ptrace too.
> > 
> > So IMA stuff does not do anything to protect against process memory being
> > modified using ptrace or by playing tricks with swap.
> 
> > I am not sure what will happen if I can bypass the file system and directly
> > write on a disk block and modify executable. (Assuming one can get block
> > information somehow). Does anything protect such modification? Will IMA
> > detect it?
> 
> Sorry, this is out of scope for IMA.  Dmitry has looked into this, but
> I'm not sure where it stands at the moment.

Ok, so that's one reason that why I wrote these patcehs. IMA currently
is not doing following things to make sure address space of signed images
is not modified by others.

- Protecting against modifications to pages on swap.
- Protecting against modifications by ptrace.
- Protecting against modifications which bypassed filesystem and directly
  wrote to the block.
 
Locking down all the pages of signed binaries in memory hopefully should
solve above problems.

Thanks
Vivek
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