linux-kernel - Re: [patch 2/6] mmu_notifier: Callbacks to invalidate address ranges

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:	Tue, 29 Jan 2008 14:55:56 -0800 (PST)
From:	Christoph Lameter <clameter@....com>
To:	Andrea Arcangeli <andrea@...ranet.com>
cc:	Robin Holt <holt@....com>, Avi Kivity <avi@...ranet.com>,
	Izik Eidus <izike@...ranet.com>, Nick Piggin <npiggin@...e.de>,
	kvm-devel@...ts.sourceforge.net,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>, steiner@....com,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	daniel.blueman@...drics.com, Hugh Dickins <hugh@...itas.com>
Subject: Re: [patch 2/6] mmu_notifier: Callbacks to invalidate address ranges

On Tue, 29 Jan 2008, Andrea Arcangeli wrote:

> But now I think there may be an issue with a third thread that may
> show unsafe the removal of invalidate_page from ptep_clear_flush.
> 
> A third thread writing to a page through the linux-pte and the guest
> VM writing to the same page through the sptes, will be writing on the
> same physical page concurrently and using an userspace spinlock w/o
> ever entering the kernel. With your patch that invalidate_range after
> dropping the PT lock, the third thread may start writing on the new
> page, when the guest is still writing to the old page through the
> sptes. While this couldn't happen with my patch.

A user space spinlock plays into this??? That is irrelevant to the kernel. 
And we are discussing "your" placement of the invalidate_range not mine.

This is the scenario that I described before. You just need two threads.
One thread is in do_wp_page and the other is writing through the spte. 
We are in do_wp_page. Meaning the page is not writable. The writer will 
have to take fault which will properly serialize access. It a bug if the 
spte would allow write.

--
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/