From mboxrd@z Thu Jan  1 00:00:00 1970
From: David Howells <dhowells@redhat.com>
Subject: Re: [PATCH 18/27] bpf: Restrict kernel image access functions when the kernel is locked down
Date: Thu, 19 Oct 2017 23:48:34 +0100
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To: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Cc: jlee@suse.com, dhowells@redhat.com, linux-security-module@vger.kernel.org, gnomes@lxorguk.ukuu.org.uk, linux-efi@vger.kernel.org, gregkh@linuxfoundation.org, linux-kernel@vger.kernel.org, jforbes@redhat.com, Daniel Borkmann <daniel@iogearbox.net>, "David S. Miller" <davem@davemloft.net>, netdev@vger.kernel.org
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Alexei Starovoitov <alexei.starovoitov@gmail.com> wrote:

> > @@ -65,6 +65,11 @@ BPF_CALL_3(bpf_probe_read, void *, dst, u32, size, const void *, unsafe_ptr)
> >  {
> >  	int ret;
> >  
> > +	if (kernel_is_locked_down("BPF")) {
> > +		memset(dst, 0, size);
> > +		return -EPERM;
> > +	}
>
> That doesn't help the lockdown purpose.
> If you don't trust the root the only way to prevent bpf read
> memory is to disable the whole thing.
> Have a single check in sys_bpf() to disallow everything if kernel_is_locked_down()
> and don't add overhead to critical path like bpf_probe_read().

TBH, I've no idea how bpf does anything, so I can't say whether this is
better, overkill or insufficient.

David