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Date: Tue, 6 Feb 2018 12:58:27 -0800
From: Linus Torvalds <>
To: Andy Lutomirski <>
Cc: Dan Williams <>, Luis Henriques <>, 
	Linux Kernel Mailing List <>, linux-arch <>, 
	Kernel Hardening <>, Greg KH <>, 
	X86 ML <>, Ingo Molnar <>, "H. Peter Anvin" <>, 
	Thomas Gleixner <>, Andrew Morton <>, 
	Alan Cox <>
Subject: Re: [PATCH v4 07/10] x86: narrow out of bounds syscalls to sys_read
 under speculation

On Tue, Feb 6, 2018 at 12:49 PM, Andy Lutomirski <> wrote:
> Can you use @cc to make an asm statement that outputs both the masked
> array index and the "if" condition?  I can never remember the syntax,
> but something like:

Yes. Although I'd actually suggest just using an "asm goto" if we
really want to optimize this. Give the "index_mask_nospec()" a third
argument that is the label to jump to for overflow.

Then you can just decide how to implement it best for any particular
architecture (and compiler limitation).


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