From: Alexei Starovoitov <alexei.starovoitov@gmail.com>
To: Kees Cook <keescook@chromium.org>
Cc: Casey Schaufler <casey@schaufler-ca.com>,
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
Subject: Re: [PATCH bpf-next v4 3/8] bpf: lsm: provide attachment points for BPF LSM programs
Date: Mon, 24 Feb 2020 21:41:27 -0800 [thread overview]
Message-ID: <20200225054125.dttrc3fvllzu4mx5@ast-mbp> (raw)
In-Reply-To: <202002241136.C4F9F7DFF@keescook>
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.
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.
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.
next prev parent reply other threads:[~2020-02-25 5:41 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 [this message]
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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