Re: [PATCH 16/18] net: mpls: prevent bounds-check bypass via speculative execution
From: Linus Torvalds <torvalds@linux-foundation.org>
Date: 2018-01-09 04:21:13
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On Mon, Jan 8, 2018 at 8:13 PM, Linus Torvalds [off-list ref] wrote:
# carry will be clear if idx >= max
cmpq %idx,%max
Bah. Other way around.
cmpq %max,%idx
I'm a moron.
# mask will be clear if carry was clear, ~0 otherwise
sbbq %mask,%mask
to generate mask directly. I might have screwed that up. Worth perhaps trying?
More importantly, worth _testing_ and fixing my hand-waving "asm like
this" crap.
But I do think that simple two-instruction cmpq/sbbq sequence could
get it right in just two trivial ALU instructions.
Linus