linux-kernel - Re: An actual suggestion (Re: [GIT PULL] Kernel lockdown for secure boot)

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Date:   Thu, 5 Apr 2018 09:48:20 +0800
From:   joeyli <jlee@...e.com>
To:     David Howells <dhowells@...hat.com>
Cc:     Jann Horn <jannh@...gle.com>, Alexei Starovoitov <ast@...nel.org>,
        Andy Lutomirski <luto@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Theodore Y. Ts'o" <tytso@....edu>,
        Matthew Garrett <mjg59@...gle.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        James Morris <jmorris@...ei.org>,
        Alan Cox <gnomes@...rguk.ukuu.org.uk>,
        Linux Kernel Mailing List <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>
Subject: Re: An actual suggestion (Re: [GIT PULL] Kernel lockdown for secure
 boot)

On Wed, Apr 04, 2018 at 11:19:27PM +0100, David Howells wrote:
> Jann Horn <jannh@...gle.com> wrote:
> 
> > > Uh, no.  bpf, for example, can be used to modify kernel memory.
> > 
> > I'm pretty sure bpf isn't supposed to be able to modify arbitrary
> > kernel memory. AFAIU if you can use BPF to write to arbitrary kernel
> > memory, that's a bug; with CAP_SYS_ADMIN, you can read from userspace,
> > write to userspace, and read from kernelspace, but you shouldn't be
> > able to write to kernelspace.
> 
> Ah - you may be right.  I seem to have misremembered what Joey Lee wrote in
> his patch description.
>

Sorry for it's my fault to misunderstood the behavoir of bpf with
CAP_SYS_ADMIN.

Joey Lee