linux-kernel - Re: [PATCH] x86-64: espfix for 64-bit mode *PROTOTYPE*

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Message-ID: <535F20D3.1050407@linux.intel.com>
Date:	Mon, 28 Apr 2014 20:47:31 -0700
From:	"H. Peter Anvin" <hpa@...ux.intel.com>
To:	"H. Peter Anvin" <hpa@...or.com>,
	Andrew Lutomirski <amluto@...il.com>
CC:	comex <comexk@...il.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...nel.org>,
	Alexander van Heukelum <heukelum@...tmail.fm>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	Borislav Petkov <bp@...en8.de>,
	Arjan van de Ven <arjan.van.de.ven@...el.com>,
	Brian Gerst <brgerst@...il.com>,
	Alexandre Julliard <julliard@...ehq.com>,
	Andi Kleen <andi@...stfloor.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] x86-64: espfix for 64-bit mode *PROTOTYPE*

On 04/28/2014 08:45 PM, H. Peter Anvin wrote:
> 
> OK, so I found a bug in ldttest.c -- it sets CS to an LDT segment, but
> it never sets SS to an LDT segment.  This means that it should really
> have zero footprint versus the espfix code, and implies that we instead
> have another bug involved.  Why the espfix code should have any effect
> whatsoever is a mystery, however... if it indeed does?
> 
> I have uploaded a fixed ldttest.c, but it seems we might be chasing more
> than that...
> 

In particular, I was already wondered how we avoid an "upside down
swapgs" with a #GP on IRET.  The answer might be that we don't...

	-hpa


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