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From:   Alexei Starovoitov <alexei.starovoitov@gmail.com>
Date:   Fri, 4 Jun 2021 17:08:24 -0700
Message-ID: <CAADnVQ+0bNtDj46Q8s-h=rqJgZz2JaGTeHpbmof3e7fBBQKuDQ@mail.gmail.com>
Subject: Re: [PATCH v2] lockdown,selinux: avoid bogus SELinux lockdown
 permission checks
To:     Paul Moore <paul@paul-moore.com>
Cc:     Daniel Borkmann <daniel@iogearbox.net>,
        Ondrej Mosnacek <omosnace@redhat.com>,
        LSM List <linux-security-module@vger.kernel.org>,
        James Morris <jmorris@namei.org>,
        Steven Rostedt <rostedt@goodmis.org>,
        Ingo Molnar <mingo@redhat.com>,
        Stephen Smalley <stephen.smalley.work@gmail.com>,
        selinux@vger.kernel.org, ppc-dev <linuxppc-dev@lists.ozlabs.org>,
        Linux-Fsdevel <linux-fsdevel@vger.kernel.org>,
        bpf <bpf@vger.kernel.org>,
        Network Development <netdev@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Casey Schaufler <casey@schaufler-ca.com>,
        Jiri Olsa <jolsa@redhat.com>,
        Alexei Starovoitov <ast@kernel.org>,
        Andrii Nakryiko <andrii@kernel.org>,
        "David S. Miller" <davem@davemloft.net>,
        Jakub Kicinski <kuba@kernel.org>,
        Linus Torvalds <torvalds@linux-foundation.org>
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On Fri, Jun 4, 2021 at 4:34 PM Paul Moore <paul@paul-moore.com> wrote:
>
> > Again, the problem is not limited to BPF at all. kprobes is doing register-
> > time hooks which are equivalent to the one of BPF. Anything in run-time
> > trying to prevent probe_read_kernel by kprobes or BPF is broken by design.
>
> Not being an expert on kprobes I can't really comment on that, but
> right now I'm focused on trying to make things work for the BPF
> helpers.  I suspect that if we can get the SELinux lockdown
> implementation working properly for BPF the solution for kprobes won't
> be far off.

Paul,

Both kprobe and bpf can call probe_read_kernel==copy_from_kernel_nofault
from all contexts.
Including NMI. Most of audit_log_* is not acceptable.
Just removing a wakeup is not solving anything.
Audit hooks don't belong in NMI.
Audit design needs memory allocation. Hence it's not suitable
for NMI and hardirq. But kprobes and bpf progs do run just fine there.
BPF, for example, only uses pre-allocated memory.