linux-kernel - Re: [tip:x86/urgent] x86-64, modify_ldt: Ban 16-bit segments on 64-bit kernels

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Message-ID: <CAMzpN2jHrBZ7DCd79GkCdjwCWJBv+YR5o9BGjypCdazJB9bJYQ@mail.gmail.com>
Date:	Sat, 12 Apr 2014 16:34:14 -0400
From:	Brian Gerst <brgerst@...il.com>
To:	Borislav Petkov <bp@...en8.de>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	stable <stable@...r.kernel.org>,
	"H. Peter Anvin" <hpa@...ux.intel.com>
Subject: Re: [tip:x86/urgent] x86-64, modify_ldt: Ban 16-bit segments on
 64-bit kernels

On Sat, Apr 12, 2014 at 4:11 PM, Borislav Petkov <bp@...en8.de> wrote:
> On Sat, Apr 12, 2014 at 12:44:42PM -0700, H. Peter Anvin wrote:
>> Run a 32-bit VM.  The 32-bit kernel does this right.
>
> Yes, even better.
>
>> I suspect it would also work fine in a Qemu user mode guest (is
>> this supported by KVM?), in a ReactOS VM, or some other number of
>> combinations.
>
> Right.
>
> So basically, there a lot of different virt scenarios which can all take
> care of those use cases *without* encumbering some insane solutions on
> 64-bit.
>
>> The real question is how many real users are actually affected.
>
> And if they are, virtualize them, for chrissake. It is time we finally
> used virt for maybe one of its major use cases - virtualize old/obscure
> hw. It should be pretty reliable by now.
>
> :-P
>
> --
> Regards/Gruss,
>     Boris.
>
> Sent from a fat crate under my desk. Formatting is fine.
> --

My experience with kvm so far is that is slow and clunky.  It may be
OK for a server environment, but interactively it's difficult to use.
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