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Date: Wed, 17 Jan 2018 11:16:50 -0800
From: Linus Torvalds <>
To: Dan Williams <>
Cc: Linux Kernel Mailing List <>,, 
	Andi Kleen <>, Kees Cook <>,, 
	Greg Kroah-Hartman <>, "the arch/x86 maintainers" <>, 
	Ingo Molnar <>, Al Viro <>, 
	"H. Peter Anvin" <>, Thomas Gleixner <>, 
	Andrew Morton <>, Alan Cox <>
Subject: Re: [PATCH v3 8/9] x86: use __uaccess_begin_nospec and ASM_IFENCE in
 get_user paths

On Tue, Jan 16, 2018 at 8:30 PM, Dan Williams <> wrote:
> I think the access_ok() conversion to return a speculation sanitized
> pointer or NULL is the way to go unless I'm missing something simpler.

No, that's way too big of a conversion.

Just make get_user() and friends (that currently use ASM_STAC) use the
address masking.

The people who use uaccess_begin() can use the lfence there.

Basically, the rule is trivial: find all 'stac' users, and use address
masking if those users already integrate the limit check, and lfence
they don't.


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