linux-kernel - Re: [RFC PATCH 00/16] PTI support for x86-32

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Message-ID: <20180122100409.GF28161@8bytes.org>
Date:   Mon, 22 Jan 2018 11:04:09 +0100
From:   Joerg Roedel <joro@...tes.org>
To:     David Laight <David.Laight@...LAB.COM>
Cc:     'Nadav Amit' <nadav.amit@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        "H . Peter Anvin" <hpa@...or.com>,
        the arch/x86 maintainers <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        "open list:MEMORY MANAGEMENT" <linux-mm@...ck.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andy Lutomirski <luto@...nel.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>,
        Denys Vlasenko <dvlasenk@...hat.com>,
        Eduardo Valentin <eduval@...zon.com>,
        Greg KH <gregkh@...uxfoundation.org>,
        Will Deacon <will.deacon@....com>,
        "aliguori@...zon.com" <aliguori@...zon.com>,
        "daniel.gruss@...k.tugraz.at" <daniel.gruss@...k.tugraz.at>,
        "hughd@...gle.com" <hughd@...gle.com>,
        "keescook@...gle.com" <keescook@...gle.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Waiman Long <llong@...hat.com>,
        "jroedel@...e.de" <jroedel@...e.de>
Subject: Re: [RFC PATCH 00/16] PTI support for x86-32

On Mon, Jan 22, 2018 at 09:55:31AM +0000, David Laight wrote:
> That's made me remember something about segment limits applying in 64bit mode.
> I really can't remember the details at all.
> I'm sure it had something to do with one of the VM implementations restricting
> memory accesses.

Some AMD chips have long-mode segment limits, not sure if Intel has them
too. But they are useless here because the limit is 32 bit and can only
protect the upper 4GB of virtual address space. The limits also don't
apply to GS and CS segements.


Regards,

	Joerg