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Date: Wed, 17 Jan 2018 20:05:32 +0000
From: Al Viro <>
To: Dan Williams <>
Cc: Alan Cox <>,
	Linus Torvalds <>,
	Linux Kernel Mailing List <>,, Andi Kleen <>,
	Kees Cook <>,,
	Greg Kroah-Hartman <>,
	the arch/x86 maintainers <>,
	Ingo Molnar <>, "H. Peter Anvin" <>,
	Thomas Gleixner <>,
	Andrew Morton <>
Subject: Re: [PATCH v3 8/9] x86: use __uaccess_begin_nospec and ASM_IFENCE in
 get_user paths

On Wed, Jan 17, 2018 at 11:54:12AM -0800, Dan Williams wrote:
> On Wed, Jan 17, 2018 at 10:52 AM, Al Viro <> wrote:
> > On Wed, Jan 17, 2018 at 02:17:26PM +0000, Alan Cox wrote:
> [..]
> >         Incidentally, what about copy_to_iter() and friends?  They
> > check iov_iter flavour and go either into the "copy to kernel buffer"
> > or "copy to userland" paths.  Do we need to deal with mispredictions
> > there?  We are calling a bunch of those on read()...
> >
> Those should be protected by the conversion of __uaccess_begin to
> __uaccess_begin_nospec that includes the lfence.

Huh?  What the hell does it do to speculative execution of "memcpy those
suckers" branch?

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