linux-kernel - Re: [PATCH v2 2/2] kernel/trace: Remove function callback casts

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Message-ID: <20200724172403.GC3123@ubuntu>
Date:   Fri, 24 Jul 2020 19:24:03 +0200
From:   Oscar Carter <oscar.carter@....com>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Oscar Carter <oscar.carter@....com>,
        Ingo Molnar <mingo@...hat.com>,
        Kees Cook <keescook@...omium.org>,
        linux-kernel@...r.kernel.org, kernel-hardening@...ts.openwall.com,
        Jann Horn <jannh@...gle.com>
Subject: Re: [PATCH v2 2/2] kernel/trace: Remove function callback casts

Hi Steven,

On Fri, Jul 24, 2020 at 07:14:18PM +0200, Oscar Carter wrote:
> On Fri, Jul 24, 2020 at 12:35:28PM -0400, Steven Rostedt wrote:
> > On Fri, 24 Jul 2020 18:19:21 +0200
> > Oscar Carter <oscar.carter@....com> wrote:
> >
> > > > The linker trick is far less intrusive, and I believe less error prone.
> > >
> > > If we use the linker trick, the warning -Wcast-function-type dissapears,
> > > but in a way that makes impossible to the compiler to get the necessary
> > > info about function prototypes to insert the commented check. As far I
> > > know, this linker trick (redirection of a function) is hidden for the
> > > CFI build.
> > >
> > > So, in my opinion, the linker trick is not suitable if we want to protect
> > > the function pointers of the ftrace subsystem against an attack that
> > > modifiy the normal flow of the kernel.
> >
> > The linker trick should only affect architectures that don't implement
> > the needed features. I can make it so the linker trick is only applied
> > to those archs, and other archs that want more protection only need to
> > add these features to their architectures.
> >
> > It's much less intrusive than this patch.
>
> Sorry, but I don't understand your proposal. What features an arch need to
> add if want the CFI protection?

Typo correction.

Sorry, but I don't understand your proposal. What features does an arch need
to add if want the CFI protection?

>
> >
> > -- Steve
>
Thanks,
Oscar Carter