linux-kernel - Re: [GIT PULL] Kernel lockdown for secure boot

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Message-ID: <20180409034008.dyte7k5kgkbjh5is@ast-mbp.dhcp.thefacebook.com>
Date:   Sun, 8 Apr 2018 20:40:10 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     joeyli <jlee@...e.com>
Cc:     Andy Lutomirski <luto@...nel.org>,
        David Howells <dhowells@...hat.com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        James Morris <jmorris@...ei.org>,
        One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Matthew Garrett <mjg59@...gle.com>,
        Greg KH <gregkh@...uxfoundation.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Justin Forbes <jforbes@...hat.com>,
        linux-man <linux-man@...r.kernel.org>,
        LSM List <linux-security-module@...r.kernel.org>,
        Linux API <linux-api@...r.kernel.org>,
        Kees Cook <keescook@...omium.org>,
        linux-efi <linux-efi@...r.kernel.org>,
        Daniel Borkmann <daniel@...earbox.net>
Subject: Re: [GIT PULL] Kernel lockdown for secure boot

On Sun, Apr 08, 2018 at 04:07:42PM +0800, joeyli wrote:
> 
> > If the only thing that folks are paranoid about is reading
> > arbitrary kernel memory with bpf_probe_read() helper
> > then preferred patch would be to disable it during verification
> > when in lockdown mode
> 
> Sorry for I didn't fully understand your idea...
> Do you mean that using bpf verifier to filter out bpf program that
> uses bpf_probe_read()?

Take a look bpf_get_trace_printk_proto().
Similarly we can add bpf_get_probe_read_proto() that
will return NULL if lockdown is on.
Then programs with bpf_probe_read() will be rejected by the verifier.