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

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Date:   Thu, 4 Jan 2018 21:01:48 -0500
From:   james harvey <jamespharvey20@...il.com>
To:     Jiri Kosina <jikos@...nel.org>
Cc:     Andi Kleen <andi@...stfloor.org>,
        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, Jan 3, 2018 at 7:19 PM, Jiri Kosina <jikos@...nel.org> wrote:
> On Wed, 3 Jan 2018, Andi Kleen 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.
>
> If gcc anotates indirect calls/jumps in a way that we could patch them
> using alternatives in runtime, that'd be enough.
>
> --
> Jiri Kosina
> SUSE Labs

I understand the GCC patches being discussed will fix the
vulnerability because newly compiled kernels will be compiled with a
GCC with these patches.

But, are the GCC patches being discussed also expected to fix the
vulnerability because user binaries will be compiled using them?  In
such case, a binary could be maliciously changed back, or a custom GCC
made with the patches reverted.

Please forgive me if my ignorance about all the related GCC patches
makes this a stupid question.