linux-kernel - Re: [PATCH 10/39] x86/entry/32: Handle Entry from Kernel-Mode on Entry-Stack

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Message-ID: <20180718115905.GA18541@8bytes.org>
Date:   Wed, 18 Jul 2018 13:59:05 +0200
From:   Joerg Roedel <joro@...tes.org>
To:     Andy Lutomirski <luto@...capital.net>
Cc:     Joerg Roedel <jroedel@...e.de>, Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        "H . Peter Anvin" <hpa@...or.com>, X86 ML <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Dave Hansen <dave.hansen@...el.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Juergen Gross <jgross@...e.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Borislav Petkov <bp@...en8.de>, Jiri Kosina <jkosina@...e.cz>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Brian Gerst <brgerst@...il.com>,
        David Laight <David.Laight@...lab.com>,
        Denys Vlasenko <dvlasenk@...hat.com>,
        Eduardo Valentin <eduval@...zon.com>,
        Greg KH <gregkh@...uxfoundation.org>,
        Will Deacon <will.deacon@....com>,
        "Liguori, Anthony" <aliguori@...zon.com>,
        Daniel Gruss <daniel.gruss@...k.tugraz.at>,
        Hugh Dickins <hughd@...gle.com>,
        Kees Cook <keescook@...gle.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Waiman Long <llong@...hat.com>, Pavel Machek <pavel@....cz>,
        "David H . Gutteridge" <dhgutteridge@...patico.ca>
Subject: Re: [PATCH 10/39] x86/entry/32: Handle Entry from Kernel-Mode on
 Entry-Stack

On Tue, Jul 17, 2018 at 01:06:11PM -0700, Andy Lutomirski wrote:
> Yes, we obviously need to restore the correct cr3.  But I really don't
> like the code that rewrites the stack frame that we're about to IRET
> to, especially when it doesn't seem to serve a purpose.  I'd much
> rather the code just get its CR3 right and do the IRET and trust that
> the frame it's returning to is still there.

Okay, I'll give it a try and if it works without the copying we can put
that on-top of this patch-set. This also has the benefit that we can
revert it later if it causes problems down the road.


Regards,

	Joerg