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Re: [PATCH 5/5] x86/ucode: Relax digest check when Entrysign is fixed in firmware
- To: Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- Date: Mon, 20 Oct 2025 16:06:22 +0100
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- Cc: Jan Beulich <JBeulich@xxxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>
- Delivery-date: Mon, 20 Oct 2025 15:06:41 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 20/10/2025 2:19 pm, Andrew Cooper wrote:
> When Entrysign has been mitigated in firwmare, it is believed to be safe to
> pass blobs to the CPU again. This avoids us needing to update the digest
> table for new microcodes.
>
> Relax the digest check when firmware looks to be up to date, and leave behind
> a clear message when not.
>
> This is best-effort only. If a malicious microcode has been loaded prior to
> Xen running, then all bets are off.
>
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> ---
> CC: Jan Beulich <JBeulich@xxxxxxxx>
> CC: Roger Pau Monné <roger.pau@xxxxxxxxxx>
>
> I need to double check the revision table. I think I need to submit a
> correction to Linux first.
Yes.
https://lore.kernel.org/lkml/20251020144124.2930784-1-andrew.cooper3@xxxxxxxxxx/T/#u
Also there's a general off-by-one error in the revisions, owing to a
difference in how Linux and Xen are using the boundaries.
Both fixed locally for v2.
~Andrew
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