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Date:   Thu, 5 Apr 2018 09:48:20 +0800
From:   joeyli <jlee@suse.com>
To:     David Howells <dhowells@redhat.com>
Cc:     Jann Horn <jannh@google.com>, Alexei Starovoitov <ast@kernel.org>,
        Andy Lutomirski <luto@kernel.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        "Theodore Y. Ts'o" <tytso@mit.edu>,
        Matthew Garrett <mjg59@google.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Ard Biesheuvel <ard.biesheuvel@linaro.org>,
        James Morris <jmorris@namei.org>,
        Alan Cox <gnomes@lxorguk.ukuu.org.uk>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Justin Forbes <jforbes@redhat.com>,
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        Linux API <linux-api@vger.kernel.org>,
        Kees Cook <keescook@chromium.org>,
        linux-efi <linux-efi@vger.kernel.org>
Subject: Re: An actual suggestion (Re: [GIT PULL] Kernel lockdown for secure
 boot)
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On Wed, Apr 04, 2018 at 11:19:27PM +0100, David Howells wrote:
> Jann Horn <jannh@google.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