linux-kernel - Re: [PATCH] x86-64, espfix: Don't leak bits 31:16 of %esp returning to 16-bit stack

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Message-ID: <CA+55aFwTKzSgt2fk8gYbA67hfEWV6_a18Dfhw2D9jzHzs2GSEg@mail.gmail.com>
Date:	Tue, 29 Apr 2014 17:57:11 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	"H. Peter Anvin" <hpa@...ux.intel.com>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Borislav Petkov <bp@...en8.de>,
	Andrew Lutomriski <amluto@...il.com>,
	Dirk Hohndel <dirk@...ndel.org>,
	Arjan van de Ven <arjan.van.de.ven@...el.com>,
	comex <comexk@...il.com>,
	Alexander van Heukelum <heukelum@...tmail.fm>,
	Boris Ostrovsky <boris.ostrovsky@...cle.com>
Subject: Re: [PATCH] x86-64, espfix: Don't leak bits 31:16 of %esp returning
 to 16-bit stack

On Tue, Apr 29, 2014 at 5:15 PM, H. Peter Anvin <hpa@...ux.intel.com> wrote:
>
> Linus, this is technically a (functionality) regression fix.  Will you
> want this for 3.15?

Too scary. If people complain, I think we should just replace the

        if (!ldt_info.seg_32bit) {

with something like

        if (!ldt_info.seg_32bit && !sysctl_allow_16bit_segments) {

and handle the regression that way.

Then, after way more testing, maybe we can backport the espfix thing.

            Linus
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