linux-kernel - Re: Regression: x86/mm: new _PTE_SWP_SOFT_DIRTY bit conflicts with existing use

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]

Date:	Wed, 21 Aug 2013 20:19:46 +0400
From:	Cyrill Gorcunov <gorcunov@...il.com>
To:	Jan Beulich <JBeulich@...e.com>
Cc:	Andy Lutomirski <luto@...capital.net>,
	David Vrabel <david.vrabel@...rix.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Xen-devel@...ts.xen.org,
	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Pavel Emelyanov <xemul@...allels.com>,
	Ingo Molnar <mingo@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: Regression: x86/mm: new _PTE_SWP_SOFT_DIRTY bit conflicts with
 existing use

On Wed, Aug 21, 2013 at 05:03:13PM +0100, Jan Beulich wrote:
> > 
> > Only to non-present ptes, as far as I know.
> 
> That's not really any guarantee. And the accessor functions also
> don't check that they'd be used on non-present PTEs only.

Wait. This _PAGE_SWP_SOFT_DIRTY bit (which is in real PSE bit) assigned
in only one place -- in try_to_unmap_one(). The PTE get non-present then
and consists of swap entry format. I don't see any accessor to such entry
without testing if it's swap entry or pte-none. What I'm missing?

> > orig_pte has pse bit set if page has been soft dirty
> > when it reached swap.
> 
> "when it reached swap" to me again implies that it could come
> from a live page table, with the present bit set. So that
> explanation attempt of yours confuses me more than it
> clarifies things for me. (And referring to this bit as PSE bit is

When page swapped out it become non-present in pte entry.

> sort of wrong here too - there's no PSE bit for 4k PTEs, that
> bit is the PAT one, and that's what the whole discussion
> started from.)

And I asked David to point me how it happens, because I don't
understand at which point pse bit get analized when page is
not present.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/