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

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Message-ID: <CA+55aFy=do-mxp4Ufg_vNKfp0CuZmDUGHQzV059TAN8bXbiCAQ@mail.gmail.com>
Date:	Sat, 12 Apr 2014 20:13:25 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	"H. Peter Anvin" <hpa@...or.com>, 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 Sat, Apr 12, 2014 at 7:56 PM, Andi Kleen <andi@...stfloor.org> wrote:
>
> Why? Either it works or it doesn't.
>
> If it works it doesn't make any sense to have a sysctl.

BS.

It "works" exactly like mmap() at NULL "works".

It is a potential security leak, because x86-64 screwed up the
architecture definition in this area. So it should definitely be
disabled by default, exactly like mmap_min_addr is non-zero by
default.

            Linus
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