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This is bad news... and it's serious.
In short: As of July 2021, Microsoft will no longer allow new releases of drivers to be cross-signed and loaded on Windows 7, Windows 8.1, or Windows Server 2012 R2 (including Windows Embedded 8 and Windows Embedded 8.1). You can read the policy here.
Folks have raised this issue several times here in this forum in the past. One of the most recent was Mr. Roddy in this thread. I have always urged posters not to worry, because I assumed that this policy would be "corrected" -- Apparently, I have been overly optimistic.
For more than a year, folks here at OSR have been been engaged with Microsoft over this issue. Our understanding (or, perhaps, it was simply our hope) was that this policy was going to be "fixed." Surely, we reasoned, Microsoft is not going to prevent us from releasing updated drivers for versions of Windows that are still supported by Microsoft. We heard rumors that Attestation Signing would be extended to cover versions of Windows prior to Windows 10.
Apparently we were mistaken. Despite all our efforts, we have been unable to identify ANY plan that'll allow folks to release updated drivers for versions of Windows prior to Windows 10.
So, as of July 2021, if you want to update a driver that runs on a Windows version other than Windows 10... forget it. You're screwed. And, worst of all, your customers are screwed.
According to Microsoft's published plans, the only way to update a driver for a version of Windows other than Windows 10 is to have that driver pass the HLK/WHQL tests. That is, assuming that your driver falls into a category where there are HLK tests. And your driver can pass those tests. There are many, many, drivers -- especially drivers for special-purpose systems -- that will never be able to pass the HLKs and have no reason or need to pass the HLKs.
If we work together, we can get Microsoft to change this plan. This community has done it before.
Work your technical contacts. Get the message clearly presented to the folks you work with at MSFT.
Even more important, you must explain the problem to the managers at your company who regularly engage with MSFT. You must get your execs and your managers to raise this issue with their MSFT contacts.
Because if we don't change this policy, lots of Windows users are going to be put in very difficult positions.
The time to act is now, folks. Microsoft needs to hear from you and from your management team.
The clock is ticking...