linux-kernel - Re: [GIT PULL] x86/urgent for v5.11-rc7

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Message-Id: <2BFAADF3-EBAA-46D6-B1F6-7A41CB85DA1C@amacapital.net>
Date:   Sun, 7 Feb 2021 10:31:32 -0800
From:   Andy Lutomirski <luto@...capital.net>
To:     Dave Hansen <dave.hansen@...el.com>
Cc:     Borislav Petkov <bp@...e.de>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Steven Rostedt <rostedt@...dmis.org>, x86-ml <x86@...nel.org>,
        lkml <linux-kernel@...r.kernel.org>
Subject: Re: [GIT PULL] x86/urgent for v5.11-rc7


> On Feb 7, 2021, at 10:19 AM, Dave Hansen <dave.hansen@...el.com> wrote:
> 
> On 2/7/21 9:58 AM, Borislav Petkov wrote:
>>> On Sun, Feb 07, 2021 at 09:49:18AM -0800, Linus Torvalds wrote:
>>> On Sun, Feb 7, 2021 at 2:40 AM Borislav Petkov <bp@...e.de> wrote:
>>>> - Disable CET instrumentation in the kernel so that gcc doesn't add
>>>> ENDBR64 to kernel code and thus confuse tracing.
>>> So this is clearly the right thing to do for now, but I wonder if
>>> people have a plan for actually enabling CET and endbr at cpl0 at some
>>> point?
>> It probably is an item on some Intel manager's to-enable list. So far,
>> the CET enablement concentrates only on userspace but dhansen might know
>> more about future plans. CCed.
> 
> It's definitely on our radar to look at after CET userspace.
> 
> The only question for me is whether it will be worth doing with the
> exiting kernel entry/exit architecture.

I assume you mean: is anyone sufficiently inspired to try to handle NMI correctly?  I have a whole pile of nacks saved up for incorrect implementations, although I will try to wrap them in polite explanations of precisely what is wrong :)

(I’ve contemplated doing this myself, and it doesn’t sound fun at all.)