[RFC PATCH] ima: verify mprotect change is consistent with mmap policy

[Mimi Zohar]

Hi Jann,

On Tue, 2020-05-05 at 02:15 +0200, Jann Horn wrote:
> On Mon, May 4, 2020 at 11:18 PM Mimi Zohar <zohar at linux.ibm.com> wrote:
> > Files can be mmap'ed read/write and later changed to execute to circumvent
> > IMA's mmap appraise policy rules.  Due to locking issues (mmap semaphore
> > would be taken prior to i_mutex), files can not be measured or appraised at
> > this point.  Eliminate this integrity gap, by denying the mprotect
> > PROT_EXECUTE change, if an mmap appraise policy rule exists.
> 
> Just keep in mind that there are other ways to create executable
> mappings containing controlled code; e.g. PROT_EXEC with
> MAP_ANONYMOUS, or writing to /proc/self/mem (which is a debugging API
> that works entirely without ever making the VMA writable - I had an
> old series to provide LSM hooks for that stuff at
> <https://lore.kernel.org/lkml/1478142286-18427-3-git-send-email-jann@thejh.net/>,
> but I guess I must have forgotten about it or something...).

Sure.  These sound like memory attacks, which should be closed, but
are probably out of scope for IMA.

thanks,

Mimi