linux-kernel - Re: [PATCH 07/34] x86/entry/32: Restore segments before int registers

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Date:   Mon, 5 Mar 2018 22:35:50 +0100
From:   Joerg Roedel <joro@...tes.org>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Brian Gerst <brgerst@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>, Peter Anvin <hpa@...or.com>,
        the arch/x86 maintainers <x86@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-mm <linux-mm@...ck.org>,
        Andrew Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...el.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Jürgen 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>,
        David Laight <David.Laight@...lab.com>,
        Denys Vlasenko <dvlasenk@...hat.com>,
        Eduardo Valentin <eduval@...zon.com>,
        Greg Kroah-Hartman <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>,
        Joerg Roedel <jroedel@...e.de>
Subject: Re: [PATCH 07/34] x86/entry/32: Restore segments before int registers

On Mon, Mar 05, 2018 at 12:50:33PM -0800, Linus Torvalds wrote:
> On Mon, Mar 5, 2018 at 12:38 PM, Brian Gerst <brgerst@...il.com> wrote:
> >
> > There already is a test: single_step_syscall.c
> 
> Ahh, good. So presumably Joerg actually did check it, just didn't even notice ;)

Yeah, sort of. I ran the test, but it didn't catch the failure case in
previous versions which was return to user with kernel-cr3 :)

I could probably add some debug instrumentation to check for that in my
future testing, as there is no NX protection in the user address-range
for the kernel-cr3.


	Joerg