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

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Message-ID: <20200221194149.GA9207@chromium.org>
Date:   Fri, 21 Feb 2020 20:41:49 +0100
From:   KP Singh <kpsingh@...omium.org>
To:     Casey Schaufler <casey@...aufler-ca.com>
Cc:     Linux Security Module list 
        <linux-security-module@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        James Morris <jmorris@...ei.org>,
        Kees Cook <keescook@...omium.org>
Subject: Re: [PATCH bpf-next v4 0/8] MAC and Audit policy using eBPF (KRSI)

On 21-Feb 11:19, Casey Schaufler wrote:
> On 2/20/2020 9:52 AM, KP Singh wrote:
> > From: KP Singh <kpsingh@...gle.com>
> 
> Again, apologies for the CC list trimming.
> 
> >
> > # v3 -> v4
> >
> >   https://lkml.org/lkml/2020/1/23/515
> >
> > * 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:
> >
> >     https://lore.kernel.org/bpf/CAG48ez25mW+_oCxgCtbiGMX07g_ph79UOJa07h=o_6B6+Q-u5g@mail.gmail.com/
> >
> > * 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.
       (bpf_lsm_<name>_set_enabled).

* 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
call_int_progs/call_void_progs.

- 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.
> 
>