linux-kernel - Re: [RFC] x86/speculation: add L1 Terminal Fault / Foreshadow demo

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Date:   Mon, 21 Jan 2019 20:15:41 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Andi Kleen <ak@...ux.intel.com>
Cc:     Julian Stecklina <jsteckli@...zon.de>,
        linux-kernel@...r.kernel.org,
        David Woodhouse <dwmw2@...radead.org>,
        Liran Alon <liran.alon@...cle.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Linus Torvalds <torvalds@...ux-foundation.org>, x86@...nel.org,
        Kernel Hardening <kernel-hardening@...ts.openwall.com>
Subject: Re: [RFC] x86/speculation: add L1 Terminal Fault / Foreshadow demo

On Mon, Jan 21, 2019 at 10:36:18AM -0800, Andi Kleen wrote:
> > + 	/* Check the start address: needs to be page-aligned.. */
> > +-	if (start & ~PAGE_MASK)
> > ++	if (start & ~PAGE_MASK) {
> > ++
> > ++		/*
> > ++		 * XXX Hack
> > ++		 *
> > ++		 * We re-use this error case to show case a cache load gadget:
> > ++		 * There is a mispredicted branch, which leads to prefetching
> > ++		 * the cache with attacker controlled data.
> > ++		 */
> > ++		asm volatile (
> 
> Obviously that can never be added to a standard kernel.

No, that's why it is a patch, right?  People want to test things, it's
nice to have a way to easily do this.

> And I don't see much point in shipping test cases that require non
> standard kernel patching. The idea of shipping test cases is that
> you can easily test them, but in this form it can't.

It's better than having nothing at all, which is what we have today.  So
I see no harm in it, only benefits.

thanks,

greg k-h