From: Casey Schaufler <casey@schaufler-ca.com>
To: Alexei Starovoitov <alexei.starovoitov@gmail.com>,
Kees Cook <keescook@chromium.org>
Cc: KP Singh <kpsingh@chromium.org>,
LKML <linux-kernel@vger.kernel.org>,
Linux Security Module list
<linux-security-module@vger.kernel.org>,
Alexei Starovoitov <ast@kernel.org>,
James Morris <jmorris@namei.org>,
bpf@vger.kernel.org, netdev@vger.kernel.org,
Casey Schaufler <casey@schaufler-ca.com>
Subject: Re: [PATCH bpf-next v4 3/8] bpf: lsm: provide attachment points for BPF LSM programs
Date: Mon, 24 Feb 2020 08:32:10 -0800 [thread overview]
Message-ID: <c5c67ece-e5c1-9e8f-3a2b-60d8d002c894@schaufler-ca.com> (raw)
In-Reply-To: <20200223220833.wdhonzvven7payaw@ast-mbp>
On 2/23/2020 2:08 PM, Alexei Starovoitov wrote:
> On Fri, Feb 21, 2020 at 08:22:59PM -0800, Kees Cook wrote:
>> If I'm understanding this correctly, there are two issues:
>>
>> 1- BPF needs to be run last due to fexit trampolines (?)
> no.
> The placement of nop call can be anywhere.
> BPF trampoline is automagically converting nop call into a sequence
> of directly invoked BPF programs.
> No link list traversals and no indirect calls in run-time.
Then why the insistence that it be last?
>> 2- BPF hooks don't know what may be attached at any given time, so
>> ALL LSM hooks need to be universally hooked. THIS turns out to create
>> a measurable performance problem in that the cost of the indirect call
>> on the (mostly/usually) empty BPF policy is too high.
> also no.
Um, then why not use the infrastructure as is?
>> So, trying to avoid the indirect calls is, as you say, an optimization,
>> but it might be a needed one due to the other limitations.
> I'm convinced that avoiding the cost of retpoline in critical path is a
> requirement for any new infrastructure in the kernel.
Sorry, I haven't gotten that memo.
> Not only for security, but for any new infra.
The LSM infrastructure ain't new.
> Networking stack converted all such places to conditional calls.
> In BPF land we converted indirect calls to direct jumps and direct calls.
> It took two years to do so. Adding new indirect calls is not an option.
> I'm eagerly waiting for Peter's static_call patches to land to convert
> a lot more indirect calls. May be existing LSMs will take advantage
> of static_call patches too, but static_call is not an option for BPF.
> That's why we introduced BPF trampoline in the last kernel release.
Sorry, but I don't see how BPF is so overwhelmingly special.
>> b) Would there actually be a global benefit to using the static keys
>> optimization for other LSMs?
> Yes. Just compiling with CONFIG_SECURITY adds "if (hlist_empty)" check
> for every hook.
Err, no, it doesn't. It does an hlish_for_each_entry(), which
may be the equivalent on an empty list, but let's not go around
spreading misinformation.
> Some of those hooks are in critical path. This load+cmp
> can be avoided with static_key optimization. I think it's worth doing.
I admit to being unfamiliar with the static_key implementation,
but if it would work for a list of hooks rather than a singe hook,
I'm all ears.
>> If static keys are justified for KRSI
> I really like that KRSI costs absolutely zero when it's not enabled.
And I dislike that there's security module specific code in security.c,
security.h and/or lsm_hooks.h. KRSI *is not that special*.
> Attaching BPF prog to one hook preserves zero cost for all other hooks.
> And when one hook is BPF powered it's using direct call instead of
> super expensive retpoline.
I'm not objecting to the good it does for KRSI.
I am *strongly* objecting to special casing KRSI.
> Overall this patch set looks good to me. There was a minor issue with prog
> accounting. I expect only that bit to be fixed in v5.
next prev parent reply other threads:[~2020-02-24 16:32 UTC|newest]
Thread overview: 45+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-20 17:52 [PATCH bpf-next v4 0/8] MAC and Audit policy using eBPF (KRSI) 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
2020-02-20 23:49 ` Casey Schaufler
2020-02-21 11:44 ` KP Singh
2020-02-21 18:23 ` Casey Schaufler
2020-02-22 4:22 ` Kees Cook
2020-02-23 22:08 ` Alexei Starovoitov
2020-02-24 16:32 ` Casey Schaufler [this message]
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
2020-02-24 16:09 ` Casey Schaufler
2020-02-24 17:23 ` KP Singh
2020-02-21 2:25 ` Alexei Starovoitov
2020-02-21 11:47 ` 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
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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