linux-kernel - Re: [PATCH 00/37 v6] PTI support for x86-32

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Message-ID: <20180423174506.mpbpnvfzv6fmpbzy@suse.de>
Date:   Mon, 23 Apr 2018 19:45:06 +0200
From:   Joerg Roedel <jroedel@...e.de>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Joerg Roedel <joro@...tes.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        "H . 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>, 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>,
        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 00/37 v6] PTI support for x86-32

On Mon, Apr 23, 2018 at 09:45:38AM -0700, Linus Torvalds wrote:
> Just one question: have you checked the page table setup for the
> basics wrt the USER bit in particular?

Just checked that and there are no pages with GLB and USR set, not even
a vdso page.

> No global pages should be marked PAGE_USER, with the possible
> exception of that nasty old vsyscall page.

The vsyscall page does not exist on plain 32 bit, no? All I could find
there is the vdso page, and that has no compat mapping anymore in recent
upstream kernels. To my understanding the vdso page is mapped into the
user-space portion of the address space. At least that is what I found
while looking at this, but I might have missed something.

I actually ran into a vdso issue when porting these changes to 3.0
(where there still is a compat vdso mapping in the fixmap) so I checked
my upstream code too, but didn't find the code to setup a vdso in the
fixmap.

> And it would be nice to verify that the page tables for kernel
> mappings also don't have PAGE_USER on them, although again that
> vsyscall page can cause problems.

Checked that too, all USR mappings are below PAGE_OFFSET.


Regards,

	Joerg