linux-kernel - Re: [RFC PATCH v2 6/6] x86/entry/pti: don't switch PGD on when pti

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Message-ID: <4cd54266-84b4-d2b8-fed8-12e3007a3b77@linux.intel.com>
Date:   Thu, 11 Jan 2018 12:00:08 -0800
From:   Dave Hansen <dave.hansen@...ux.intel.com>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     Willy Tarreau <w@....eu>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        LKML <linux-kernel@...r.kernel.org>, X86 ML <x86@...nel.org>,
        Borislav Petkov <bp@...en8.de>,
        Brian Gerst <brgerst@...il.com>,
        Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Kees Cook <keescook@...omium.org>
Subject: Re: [RFC PATCH v2 6/6] x86/entry/pti: don't switch PGD on when
 pti_disable is set

On 01/11/2018 09:02 AM, Andy Lutomirski wrote:
>> But, the stack gets really fun because of NMIs.
>>
>> I'm sure Andy Lutomirski has some ideas too.
> I was thinking that maybe we should add a new field or two to pt_regs.
> They could store CR2 and maybe CR3 as well.  I'd also like to expose
> the error code of exceptions in stack traces.  We should get this
> integrated right into the unwinder.

The trampoline and (normal) interrupt stacks should be pretty doable.

It's the NMI mess that I'm worried about.  I tried to change the stack
layout in there once and ran away screaming.