Messages in this thread | | | Date | Mon, 15 Aug 2022 12:29:11 +0000 | From | Ashok Raj <> | Subject | Re: [PATCH 3/5] x86/microcode/intel: Allow a late-load only if a min rev is specified |
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On Mon, Aug 15, 2022 at 09:43:00AM +0200, Peter Zijlstra wrote: > On Sat, Aug 13, 2022 at 10:38:23PM +0000, Ashok Raj wrote: > > > The proposal here is an even simpler option. The criteria for a microcode to > > be a viable late-load candidate is that no CPUID or OS visible MSR features > > are removed with respect to an earlier version of the microcode. > > > > Pseudocode for late-load is as follows: > > > > if header.min_required_id == 0 > > This is old format microcode, block late-load > > else if current_ucode_version < header.min_required_id > > Current version is too old, block late-load of this microcode. > > else > > OK to proceed with late-load. > > What about ucode that adds CPUID bits? Since the kernel will not re-init > it will not pick up on those. But userspace might. > > Should we at all time enable CPUID intercept to ensure user visible > CPUID doesn't change?
The protection is to make sure any existing users won't experience a feature pulled under their feet.
Using new features aren't dangerous though, and should be permitted.
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