linux-kernel - Re: [PATCH 02/23] x86, kaiser: do not set _PAGE_USER for init

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Message-ID: <CALCETrWQ0W=Kp7fycZ2E9Dp84CCPOr1nEmsPom71ZAXeRYqr9g@mail.gmail.com>
Date:   Wed, 1 Nov 2017 14:24:17 -0700
From:   Andy Lutomirski <luto@...nel.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Dave Hansen <dave.hansen@...ux.intel.com>,
        "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,
        Andrew Lutomirski <luto@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Kees Cook <keescook@...gle.com>,
        Hugh Dickins <hughd@...gle.com>, X86 ML <x86@...nel.org>
Subject: Re: [PATCH 02/23] x86, kaiser: do not set _PAGE_USER for init_mm page tables

On Wed, Nov 1, 2017 at 2:11 PM, Thomas Gleixner <tglx@...utronix.de> wrote:
> On Tue, 31 Oct 2017, Dave Hansen wrote:
>
>>
>> init_mm is for kernel-exclusive use.  If someone is allocating page
>> tables in it, do not set _PAGE_USER on them.  This ensures that
>> we do *not* set NX on these page tables in the KAISER code.
>
> This changelog is confusing at best.
>
> Why is this a kaiser issue? Nothing should ever create _PAGE_USER entries
> in init_mm, right?

The vsyscall page is _PAGE_USER and lives in init_mm via the fixmap.

--Andy