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

[Vivek Goyal]

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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