linux-kernel - Re: [PATCH 08/10] NOTIFIER: Take over TIF_MCE_NOTIFY and implement task return notifier

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: <BANLkTi=-A5PYj8zpjGB4Xb-_VNq0qr+CGQ@mail.gmail.com>
Date:	Sun, 12 Jun 2011 22:31:58 -0700
From:	Tony Luck <tony.luck@...el.com>
To:	Borislav Petkov <bp@...64.org>
Cc:	Ingo Molnar <mingo@...e.hu>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Huang, Ying" <ying.huang@...el.com>,
	Hidetoshi Seto <seto.hidetoshi@...fujitsu.com>,
	Avi Kivity <avi@...hat.com>
Subject: Re: [PATCH 08/10] NOTIFIER: Take over TIF_MCE_NOTIFY and implement
 task return notifier

On Sun, Jun 12, 2011 at 3:38 PM, Borislav Petkov <bp@...64.org> wrote:
> On Thu, Jun 09, 2011 at 05:36:42PM -0400, Luck, Tony wrote:
>> From: Tony Luck <tony.luck@...el.com>
>>
>> Existing user return notifier mechanism is designed to catch a specific
>> cpu just as it returns to run any task in user mode.  We also need a
>> mechanism to catch a specific task.
>
> Why do we need that? I mean, in the remaining patches we end up either
> running memory_failure() or sending signals to a task. Can't we do it
> all in the user return notifier and not have a different notifier for
> each policy?

Unless I'm mis-reading the user-return-notifier code, it is possible that
we'll context switch before we get to the notifier. At that point the
user-return-notifier TIF bit is passed on from our task to the newly
run-able task. But our task is still viable, so another cpu could grab
it and start running it ... then we have a race ... will the new task
that inherited the notifier unmap the page fast enough, or will there
be a loud BANG as the original task runs right into the machine
check again.

-Tony
--
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/