linux-kernel - Re: [patch 1/2] x86_64 page fault NMI-safe

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: <AANLkTilfXUtQznSzOmO9ecoaviIt62Hv6jdUOMSRLdrF@mail.gmail.com>
Date:	Thu, 15 Jul 2010 11:43:10 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <peterz@...radead.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Steven Rostedt <rostedt@...tedt.homelinux.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Christoph Hellwig <hch@....de>, Li Zefan <lizf@...fujitsu.com>,
	Lai Jiangshan <laijs@...fujitsu.com>,
	Johannes Berg <johannes.berg@...el.com>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	Tom Zanussi <tzanussi@...il.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Andi Kleen <andi@...stfloor.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	"Frank Ch. Eigler" <fche@...hat.com>, Tejun Heo <htejun@...il.com>
Subject: Re: [patch 1/2] x86_64 page fault NMI-safe

On Thu, Jul 15, 2010 at 11:31 AM, Mathieu Desnoyers
<mathieu.desnoyers@...icios.com> wrote:
>
> Hrm, we could probably get away with only keeping the nmi_stack_nested per-cpu
> variable. The nmi_stack_ptr could be known statically if we set it at a fixed
> offset from the bottom of stack rather than using an offset relative to the top
> (which can change depending if we are nested over the kernel or userspace).
> We just have to reserve enough space for the bottom of stack.

I thought about trying that, but I don't think it's true. At least not
for the 32-bit case.

The thing is, the 32-bit case will re-use the kernel stack if it
happens in kernel space, and will thus start from a random space (and
won't push all the information anyway). So a nested NMI really doesn't
know where the original NMI stack is to be found unless we save it
off.

In the case of x86-64, I think the stack will always be at a fixed
address, and push a fixed amount of data (because we use the IST
thing). So there you could probably just use the flag, but you'd still
have to handle the 32-bit case, and quite frankly, I think it would be
much nicer if the logic could be shared for the 32-bit and 64-bit
cases.

But maybe I'm missing something.

             Linus
--
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/