linux-kernel - Re: [PATCH 22/27] Lock down kprobes

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Message-ID: <CACdnJuss=NmcxS0UoTeopYzipt53ba5GTBwQ+YtJQXLj7_Q10w@mail.gmail.com>
Date:   Tue, 26 Mar 2019 10:41:23 -0700
From:   Matthew Garrett <mjg59@...gle.com>
To:     Masami Hiramatsu <mhiramat@...nel.org>
Cc:     James Morris <jmorris@...ei.org>,
        LSM List <linux-security-module@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        David Howells <dhowells@...hat.com>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>,
        "Naveen N . Rao" <naveen.n.rao@...ux.ibm.com>,
        Anil S Keshavamurthy <anil.s.keshavamurthy@...el.com>,
        davem@...emloft.net
Subject: Re: [PATCH 22/27] Lock down kprobes

On Tue, Mar 26, 2019 at 5:30 AM Masami Hiramatsu <mhiramat@...nel.org> wrote:
>
> On Mon, 25 Mar 2019 15:09:49 -0700
> Matthew Garrett <matthewgarrett@...gle.com> wrote:
>
> > From: David Howells <dhowells@...hat.com>
> >
> > Disallow the creation of kprobes when the kernel is locked down by
> > preventing their registration.  This prevents kprobes from being used to
> > access kernel memory, either to make modifications or to steal crypto data.
>
> Hmm, if you enforce signature check of modules, those modules
> should be allowed to use kprobes?
> I think we should introduce some kind of trust inheritance from
> signed (trusted) modules.

Is there any way to install a kprobe /without/ it coming from a
module? The presumption in lockdown mode is that module signing is
enforced, so I'll admit to not being entirely clear on why this patch
is needed in that case.