Follow @Openwall on Twitter for new release announcements and other news
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Date: Wed, 17 Jan 2018 14:17:26 +0000
From: Alan Cox <alan@...ux.intel.com>
To: Linus Torvalds <torvalds@...ux-foundation.org>, Dan Williams
	 <dan.j.williams@...el.com>
Cc: Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, 
 linux-arch@...r.kernel.org, Andi Kleen <ak@...ux.intel.com>, Kees Cook
 <keescook@...omium.org>, kernel-hardening@...ts.openwall.com, Greg
 Kroah-Hartman <gregkh@...uxfoundation.org>, the arch/x86 maintainers
 <x86@...nel.org>, Ingo Molnar <mingo@...hat.com>, Al Viro
 <viro@...iv.linux.org.uk>, "H. Peter Anvin" <hpa@...or.com>, Thomas
 Gleixner <tglx@...utronix.de>, Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v3 8/9] x86: use __uaccess_begin_nospec and ASM_IFENCE
 in get_user paths

On Tue, 2018-01-16 at 14:41 -0800, Linus Torvalds wrote:
> 
> 
> On Jan 16, 2018 14:23, "Dan Williams" <dan.j.williams@...el.com>
> wrote:
> > That said, for get_user specifically, can we do something even
> > cheaper. Dave H. reminds me that any valid user pointer that gets
> > past
> > the address limit check will have the high bit clear. So instead of
> > calculating a mask, just unconditionally clear the high bit. It
> > seems
> > worse case userspace can speculatively leak something that's
> > already
> > in its address space.
> 
> That's not at all true.
> 
> The address may be a kernel address. That's the whole point of
> 'set_fs()'.

Can we kill off the remaining users of set_fs() ?

Alan

Powered by blists - more mailing lists

Confused about mailing lists and their use? Read about mailing lists on Wikipedia and check out these guidelines on proper formatting of your messages.