Re: [PATCH 16/18] net: mpls: prevent bounds-check bypass via speculative execution

[Linus Torvalds]

On Mon, Jan 8, 2018 at 8:13 PM, Linus Torvalds
<torvalds@xxxxxxxxxxxxxxxxxxxx> 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