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

[Jann Horn]

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...).