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Re: Setting constant-time mode CPU flag
- To: Demi Marie Obenour <demi@xxxxxxxxxxxxxxxxxxxxxx>
- From: Bertrand Marquis <Bertrand.Marquis@xxxxxxx>
- Date: Wed, 7 Sep 2022 10:51:55 +0000
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- Delivery-date: Wed, 07 Sep 2022 10:52:12 +0000
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- Thread-topic: Setting constant-time mode CPU flag
Hi Demi,
> On 2 Sep 2022, at 03:05, Demi Marie Obenour <demi@xxxxxxxxxxxxxxxxxxxxxx>
> wrote:
>
> On Intel chips (Ice Lake and later) and ARM64, a bit needs to be set in
This bit would not change anything on Arm currently so nothing is required for
now (and nothing has been done in Linux for ARM64).
Thanks a lot for notifying us.
Kind regards
Bertrand
> a CPU register to enforce constant-time execution. Linux plans to set
> this bit by default; Xen should do the same. See
> https://lore.kernel.org/lkml/YwgCrqutxmX0W72r@xxxxxxxxx/T/ for details.
> I recommend setting the bit unconditionally and ignoring guest attempts
> to change it.
> --
> Sincerely,
> Demi Marie Obenour (she/her/hers)
> Invisible Things Lab
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