linux-kernel - Re: [PATCH 09/30] x86, kaiser: only populate shadow page tables for userspace

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Message-ID: <a5dbe14a-b4f3-dc31-4622-70c2fe81ec82@linux.intel.com>
Date:   Wed, 22 Nov 2017 15:30:37 -0800
From:   Dave Hansen <dave.hansen@...ux.intel.com>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        moritz.lipp@...k.tugraz.at,
        Daniel Gruss <daniel.gruss@...k.tugraz.at>,
        michael.schwarz@...k.tugraz.at, richard.fellner@...dent.tugraz.at,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Kees Cook <keescook@...gle.com>,
        Hugh Dickins <hughd@...gle.com>, X86 ML <x86@...nel.org>
Subject: Re: [PATCH 09/30] x86, kaiser: only populate shadow page tables for
 userspace

On 11/21/2017 07:44 PM, Andy Lutomirski wrote:
>> So, I guess we could enforce that only PGDs with _PAGE_USER set can ever
>> be cleared.  That has a nice symmetry to it because we set the shadow
>> when we see _PAGE_USER and we would then clear the shadow when we see
>> _PAGE_USER.
> Is this code path ever hit in any case other than tearing down an LDT?

Do you mean the PGD clearing?  We use it for tearing down userspace
PGDs, but that's it.