From: KP Singh <kpsingh@chromium.org>
To: Casey Schaufler <casey@schaufler-ca.com>
Cc: Alexei Starovoitov <alexei.starovoitov@gmail.com>,
Kees Cook <keescook@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
Subject: Re: [PATCH bpf-next v4 3/8] bpf: lsm: provide attachment points for BPF LSM programs
Date: Wed, 26 Feb 2020 06:15:35 +0100 [thread overview]
Message-ID: <20200226051535.GA17117@chromium.org> (raw)
In-Reply-To: <4b56177f-8148-177b-e1e5-c98da86b3b01@schaufler-ca.com>
On 25-Feb 16:30, Casey Schaufler wrote:
> On 2/24/2020 9:41 PM, Alexei Starovoitov wrote:
> > On Mon, Feb 24, 2020 at 01:41:19PM -0800, Kees Cook wrote:
> >> But the LSM subsystem doesn't want special cases (Casey has worked very
> >> hard to generalize everything there for stacking). It is really hard to
> >> accept adding a new special case when there are still special cases yet
> >> to be worked out even in the LSM code itself[2].
> >> [2] Casey's work to generalize the LSM interfaces continues and it quite
> >> complex:
> >> https://lore.kernel.org/linux-security-module/20200214234203.7086-1-casey@schaufler-ca.com/
> > I think the key mistake we made is that we classified KRSI as LSM.
> > LSM stacking, lsmblobs that the above set is trying to do are not necessary for KRSI.
> > I don't see anything in LSM infra that KRSI can reuse.
> > The only thing BPF needs is a function to attach to.
> > It can be a nop function or any other.
> > security_*() functions are interesting from that angle only.
> > Hence I propose to reconsider what I was suggesting earlier.
> > No changes to secruity/ directory.
> > Attach to security_*() funcs via bpf trampoline.
> > The key observation vs what I was saying earlier is KRSI and LSM are wrong names.
> > I think "security" is also loaded word that should be avoided.
>
> No argument there.
>
> > I'm proposing to rename BPF_PROG_TYPE_LSM into BPF_PROG_TYPE_OVERRIDE_RETURN.
> >
> >> So, unless James is going to take this over Casey's objections, the path
> >> forward I see here is:
> >>
> >> - land a "slow" KRSI (i.e. one that hooks every hook with a stub).
> >> - optimize calling for all LSMs
> > I'm very much surprised how 'slow' KRSI is an option at all.
> > 'slow' KRSI means that CONFIG_SECURITY_KRSI=y adds indirect calls to nop
> > functions for every place in the kernel that calls security_*().
> > This is not an acceptable overhead. Even w/o retpoline
> > this is not something datacenter servers can use.
>
> In the universe I live in data centers will disable hyper-threading,
> reducing performance substantially, in the face of hypothetical security
> exploits. That's a massively greater performance impact than the handful
> of instructions required to do indirect calls. Not to mention the impact
Indirect calls have worse performance implications than just a few
instructions and are especially not suitable for hotpaths.
There have been multiple efforts to reduce their usage e.g.:
- https://lwn.net/Articles/774743/
- https://lwn.net/Articles/773985/
> of the BPF programs that have been included. Have you ever looked at what
BPF programs are JIT'ed and optimized to native code.
> happens to system performance when polkitd is enabled?
However, let's discuss all this separately when we follow-up with
performance improvements after submitting the initial patch-set.
>
>
> >
> > Another option is to do this:
> > diff --git a/include/linux/security.h b/include/linux/security.h
> > index 64b19f050343..7887ce636fb1 100644
> > --- a/include/linux/security.h
> > +++ b/include/linux/security.h
> > @@ -240,7 +240,7 @@ static inline const char *kernel_load_data_id_str(enum kernel_load_data_id id)
> > return kernel_load_data_str[id];
> > }
> >
> > -#ifdef CONFIG_SECURITY
> > +#if defined(CONFIG_SECURITY) || defined(CONFIG_BPF_OVERRIDE_RETURN)
> >
> > Single line change to security.h and new file kernel/bpf/override_security.c
> > that will look like:
> > int security_binder_set_context_mgr(struct task_struct *mgr)
> > {
> > return 0;
> > }
> >
> > int security_binder_transaction(struct task_struct *from,
> > struct task_struct *to)
> > {
> > return 0;
> > }
> > Essentially it will provide BPF side with a set of nop functions.
> > CONFIG_SECURITY is off. It may seem as a downside that it will force a choice
> > on kernel users. Either they build the kernel with CONFIG_SECURITY and their
> > choice of LSMs or build the kernel with CONFIG_BPF_OVERRIDE_RETURN and use
> > BPF_PROG_TYPE_OVERRIDE_RETURN programs to enforce any kind of policy. I think
> > it's a pro not a con.
>
> Err, no. All distros use an LSM or two. Unless you can re-implement SELinux
The users mentioned here in this context are (I would assume) the more
performance sensitive users who would, potentially, disable
CONFIG_SECURITY because of the current performance characteristics.
We can also discuss this separately and only if we find that we need
it for the BPF_OVERRIDE_RET type attachment.
- KP
> in BPF (good luck with state transitions) you've built a warp drive without
> ever having mined dilithium crystals.
>
>
next prev parent reply other threads:[~2020-02-26 5:15 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
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 [this message]
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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