linux-kernel - Re: Proof-of-concept: better(?) page-table manipulation API

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20180504211244.GD29829@bombadil.infradead.org>
Date:   Fri, 4 May 2018 14:12:44 -0700
From:   Matthew Wilcox <willy@...radead.org>
To:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andy Lutomirski <luto@...capital.net>, x86@...nel.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: Proof-of-concept: better(?) page-table manipulation API

On Tue, Apr 24, 2018 at 06:43:56PM +0300, Kirill A. Shutemov wrote:
> +struct pt_ptr {
> +	unsigned long *ptr;
> +	int lvl;
> +};

On x86, you've got three kinds of paging scheme, referred to in the manual
as 32-bit, PAE and 4-level.  On 32-bit, you've got 3 levels (Directory,
Table and Entry), and you can encode those three levels in the bottom
two bits of the pointer.  With PAE and 4L, pointers are 64-bit aligned,
so you can encode up to eight levels in the bottom three bits of the
pointer.

> +struct pt_val {
> +	unsigned long val;
> +	int lvl;
> +};

I don't think it's possible to shrink this down to a single ulong.
_Maybe_ it is if you can squirm a single bit free from the !pte_present
case.

... this is only for x86 4L and maybe 32 paging, right?  It'd need to
use unsigned long val[2] for PAE.

I'm going to think about this some more.  There's a lot of potential here.