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

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Message-ID: <5349BD3F.6000402@zytor.com>
Date:	Sat, 12 Apr 2014 15:25:03 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
CC:	Borislav Petkov <bp@...en8.de>, Brian Gerst <brgerst@...il.com>,
	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 04/12/2014 02:53 PM, Linus Torvalds wrote:
> On Sat, Apr 12, 2014 at 12:44 PM, H. Peter Anvin <hpa@...or.com> wrote:
>> Run a 32-bit VM.  The 32-bit kernel does this right.
> 
> I really don't think that's the answer.
> 
> If people really run these 16-bit programs, we need to allow it.
> Clearly it used to work.
> 
> Just make the unconditional "don't allow 16-bit segments" be a sysconf entry.
> 

Well, is there more than one user, really... that's my question.

But yes, we can make it configurable, but the default should almost
certainly be off.

	-hpa


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