linux-kernel - Re: Avoid speculative indirect calls in kernel

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Message-ID: <20180104002916.3ff66581@alans-desktop>
Date:   Thu, 4 Jan 2018 00:29:16 +0000
From:   Alan Cox <gnomes@...rguk.ukuu.org.uk>
To:     Andi Kleen <andi@...stfloor.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Greg Kroah-Hartman <gregkh@...ux-foundation.org>,
        dwmw@...zon.co.uk, Tim Chen <tim.c.chen@...ux.intel.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Dave Hansen <dave.hansen@...el.com>
Subject: Re: Avoid speculative indirect calls in kernel

On Wed, 3 Jan 2018 16:15:01 -0800
Andi Kleen <andi@...stfloor.org> wrote:

> > It should be a CPU_BUG bit as we have for the other mess. And that can be
> > used for patching.  
> 
> It has to be done at compile time because it requires a compiler option.
> 
> Most of the indirect calls are in C code.
> 
> So it cannot just patched in, only partially out.

You can replace the pushl ; jmp  with an alternatives section (although
there might be a lot of them). Even if gcc isn't smart enough to do that
perl is.

Alan