Re: [PATCH bpf-next v4 0/8] MAC and Audit policy using eBPF (KRSI)

From: KP Singh
Date: Fri Feb 21 2020 - 14:41:55 EST

On 21-Feb 11:19, Casey Schaufler wrote:
> On 2/20/2020 9:52 AM, KP Singh wrote:
> > From: KP Singh <kpsingh@xxxxxxxxxx>
> Again, apologies for the CC list trimming.
> >
> > # v3 -> v4
> >
> >
> >
> > * Moved away from allocating a separate security_hook_heads and adding a
> > new special case for arch_prepare_bpf_trampoline to using BPF fexit
> > trampolines called from the right place in the LSM hook and toggled by
> > static keys based on the discussion in:
> >
> >
> >
> > * Since the code does not deal with security_hook_heads anymore, it goes
> > from "being a BPF LSM" to "BPF program attachment to LSM hooks".
> I've finally been able to review the entire patch set.
> I can't imagine how it can make sense to add this much
> complexity to the LSM infrastructure in support of this
> feature. There is macro magic going on that is going to
> break, and soon. You are introducing dependencies on BPF
> into the infrastructure, and that's unnecessary and most
> likely harmful.

We will be happy to document each of the macros in detail. Do note a
few things here:

* There is really nothing magical about them though, the LSM hooks are
collectively declared in lsm_hook_names.h and are used to delcare
the security_list_options and security_hook_heads for the LSM
framework (this was previously maitained in two different places):

For BPF, they declare:

* bpf_lsm_<name> attachment points and their prototypes.
* A static key (bpf_lsm_key_<name>) to enable and disable these
hooks with a function to set its value i.e.

* We have kept the BPF related macros out of security/.
* All the BPF calls in the LSM infrastructure are guarded by
CONFIG_BPF_LSM (there are only two main calls though, i.e.
call_int_hook, call_void_hook).

Honestly, the macros aren't any more complicated than

- KP

> Would you please drop the excessive optimization? I understand
> that there's been a lot of discussion and debate about it,
> but this implementation is out of control, disruptive, and
> dangerous to the code around it.