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Date:   Fri, 24 Jul 2020 19:14:18 +0200
From:   Oscar Carter <oscar.carter@gmx.com>
To:     Steven Rostedt <rostedt@goodmis.org>
Cc:     Oscar Carter <oscar.carter@gmx.com>,
        Ingo Molnar <mingo@redhat.com>,
        Kees Cook <keescook@chromium.org>,
        linux-kernel@vger.kernel.org, kernel-hardening@lists.openwall.com,
        Jann Horn <jannh@google.com>
Subject: Re: [PATCH v2 2/2] kernel/trace: Remove function callback casts
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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@gmx.com> wrote:
>
> > > The linker trick is far less intrusive, and I believe less error pro=
ne.
> >
> > If we use the linker trick, the warning -Wcast-function-type dissapear=
s,
> > but in a way that makes impossible to the compiler to get the necessar=
y
> > 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 prot=
ect
> > 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?

>
> -- Steve

Thanks,
Oscar Carter