linux-kernel - Re: [PATCH 26/30] Lock down ftrace

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Message-ID: <nycvar.YFH.7.76.1711101114410.32604@cbobk.fhfr.pm>
Date:   Fri, 10 Nov 2017 11:15:56 +0100 (CET)
From:   Jiri Kosina <jikos@...nel.org>
To:     David Howells <dhowells@...hat.com>
cc:     Alexei Starovoitov <alexei.starovoitov@...il.com>,
        linux-security-module@...r.kernel.org, gnomes@...rguk.ukuu.org.uk,
        linux-efi@...r.kernel.org, linux-kernel@...r.kernel.org,
        jforbes@...hat.com
Subject: Re: [PATCH 26/30] Lock down ftrace

On Fri, 10 Nov 2017, David Howells wrote:

> > I fail to see how this fits into the secure boot security model, could you 
> > please explain?
> 
> The idea is to prevent cryptographic data for filesystems and other things
> from being read out of the kernel memory as well as to prevent unauthorised
> modification of kernel memory.

Then it would make sense to actually lock down dumping of registers / 
function arguments (kprobes can currently do that, ftrace eventually could 
as well I guess), but disabling the whole ftrace altogether seems like a 
totally unnecessary overkill.

> > Secure boot is about having a constant proof / verification that the code 
> > you're running in ring0 can be trusted (IOW is the one that has been 
> > signed and verified by the whole boot chain).
> > 
> > Checking execution patterns doesn't seem to fit at all.
> 
> I'll defer this question to Alexei since he suggested I needed to deal 
> with this too.

Thanks.

-- 
Jiri Kosina
SUSE Labs