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From: Kees Cook <keescook@chromium.org>
To: Casey Schaufler <casey@schaufler-ca.com>
Cc: KP Singh <kpsingh@chromium.org>,
	Linux Security Module list 
	<linux-security-module@vger.kernel.org>,
	LKML <linux-kernel@vger.kernel.org>, bpf <bpf@vger.kernel.org>,
	James Morris <jmorris@namei.org>
Subject: Re: [PATCH bpf-next v4 0/8] MAC and Audit policy using eBPF (KRSI)
Date: Fri, 21 Feb 2020 16:22:59 -0800
Message-ID: <202002211617.28EAC6826@keescook> (raw)
In-Reply-To: <8a2a2d59-ec4b-80d1-2710-c2ead588e638@schaufler-ca.com>

On Fri, Feb 21, 2020 at 02:31:18PM -0800, Casey Schaufler wrote:
> On 2/21/2020 11:41 AM, KP Singh wrote:
> > On 21-Feb 11:19, Casey Schaufler wrote:
> >> On 2/20/2020 9:52 AM, KP Singh wrote:
> >>> From: KP Singh <kpsingh@google.com>
> >>> # 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,
> 
> 
> +#define LSM_HOOK_void(NAME, ...) \
> +	noinline void bpf_lsm_##NAME(__VA_ARGS__) {}
> +
> +#include <linux/lsm_hook_names.h>
> +#undef LSM_HOOK
> 
> I haven't seen anything this ... novel ... in a very long time.
> I see why you want to do this, but you're tying the two sets
> of code together unnaturally. When (not if) the two sets diverge
> you're going to be introducing another clever way to deal with
> the special case.

I really like this approach: it actually _simplifies_ the LSM piece in
that there is no need to keep the union and the hook lists in sync any
more: they're defined once now. (There were already 2 lists, and this
collapses the list into 1 place for all 3 users.) It's very visible in
the diffstat too (~300 lines removed):

 include/linux/lsm_hook_names.h | 353 +++++++++++++++++++
 include/linux/lsm_hooks.h      | 622 +--------------------------------
 2 files changed, 359 insertions(+), 616 deletions(-)

Also, there is no need to worry about divergence: the BPF will always
track the exposed LSM. Backward compat is (AIUI) explicitly a
non-feature.

I don't see why anything here is "harmful"?

-- 
Kees Cook

  parent reply index

Thread overview: 41+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-02-20 17:52 KP Singh
2020-02-20 17:52 ` [PATCH bpf-next v4 1/8] bpf: Introduce BPF_PROG_TYPE_LSM KP Singh
2020-02-20 17:52 ` [PATCH bpf-next v4 2/8] security: Refactor declaration of LSM hooks KP Singh
2020-02-20 17:52 ` [PATCH bpf-next v4 3/8] bpf: lsm: provide attachment points for BPF LSM programs KP Singh
2020-02-21  2:25   ` Alexei Starovoitov
2020-02-21 11:47     ` KP Singh
     [not found]   ` <0ef26943-9619-3736-4452-fec536a8d169@schaufler-ca.com>
2020-02-21 11:44     ` KP Singh
2020-02-21 18:23       ` Casey Schaufler
     [not found]     ` <202002211946.A23A987@keescook>
2020-02-23 22:08       ` Alexei Starovoitov
2020-02-24 16:32         ` Casey Schaufler
2020-02-24 17:13           ` KP Singh
2020-02-24 18:45             ` Casey Schaufler
2020-02-24 21:41               ` Kees Cook
2020-02-24 22:29                 ` Casey Schaufler
2020-02-25  5:41                 ` Alexei Starovoitov
2020-02-25 15:31                   ` Kees Cook
2020-02-25 19:31                   ` KP Singh
2020-02-26  0:30                   ` Casey Schaufler
2020-02-26  5:15                     ` KP Singh
2020-02-26 15:35                       ` Casey Schaufler
2020-02-25 19:29                 ` KP Singh
2020-02-20 17:52 ` [PATCH bpf-next v4 4/8] bpf: lsm: Add support for enabling/disabling BPF hooks KP Singh
2020-02-21 18:57   ` Casey Schaufler
2020-02-21 19:11     ` James Morris
2020-02-22  4:26   ` Kees Cook
2020-02-20 17:52 ` [PATCH bpf-next v4 5/8] bpf: lsm: Implement attach, detach and execution KP Singh
2020-02-21  2:17   ` Alexei Starovoitov
2020-02-21 12:02     ` KP Singh
2020-02-20 17:52 ` [PATCH bpf-next v4 6/8] tools/libbpf: Add support for BPF_PROG_TYPE_LSM KP Singh
2020-02-25  6:45   ` Andrii Nakryiko
2020-02-20 17:52 ` [PATCH bpf-next v4 7/8] bpf: lsm: Add selftests " KP Singh
2020-02-20 17:52 ` [PATCH bpf-next v4 8/8] bpf: lsm: Add Documentation KP Singh
2020-02-21 19:19 ` [PATCH bpf-next v4 0/8] MAC and Audit policy using eBPF (KRSI) Casey Schaufler
2020-02-21 19:41   ` KP Singh
2020-02-21 22:31     ` Casey Schaufler
2020-02-21 23:09       ` KP Singh
2020-02-21 23:49         ` Casey Schaufler
2020-02-22  0:22       ` Kees Cook [this message]
2020-02-22  1:04         ` Casey Schaufler
2020-02-22  3:36           ` Kees Cook
2020-02-27 18:40 ` Dr. Greg

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