[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [PATCH] x86/microcode: Prevent attempting updates known to fail
On Fri, Jun 02, 2023 at 09:35:56PM +0100, Andrew Cooper wrote: > For this MCU_CONTROL_DIS_MCU_LOAD case, we don't want to be trying to > load new microcode because that's a waste of time, but we absolutely > should query the current microcode revision. It is frequently relevant > for security reasons. > > So I think we want to fine-grain things a little, and separate the > concepts of "ucode info available" and "ucode loading available". Per > the current mechanism, that would involve supporting a case where > ucode_ops.collect_cpu_info() is available but > ucode_ops.apply_microcode() is not. I was going after something to that effect, yes. > > ~Andrew > > P.S. also in our copious free time, we need to start supporting the > Intel min_rev field, which is more complicated than it sounds. > > min_rev is vaguely defined as being relevant to block updates "after > you've evaluated CPUID and made decisions based on it", but here in Xen > we do also do livepatching and late loading to explicitly make use of > newly enumerated features. > > So we need a way of xen-ucode saying "please really do load this, > because I as the admin think it will be fine in combination with the > livepatch I'm about to apply". > > My best idea for this is to have a `--force` option to pass to Xen to > skip the revision checks, which will require either a new hypercall, or > perhaps borrowing a high bit from the size field in the current hypercall. > > With a force option in place, the boot time ucode=allow-same can go > away. It has become distinctly less useful now that we were forced do > this unilaterally on AMD CPUs, and separating "allow same because of HW > bugs" from "the Admin promised they knew what they were doing" would be > better for testing. I've created a GitLab issue to keep track of that: https://gitlab.com/xen-project/xen/-/issues/164 There's also the case of downgrades. We probably want to at least avoid going back to a microcode revision with different min_rev field. Alejandro
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