x86/ucode/amd: Handle length sanity check failures more gracefully

x86/ucode/amd: Handle length sanity check failures more gracefully

Currently, a failure of verify_patch_size() causes an early abort of the
microcode blob loop, which in turn causes a second go around the main
container loop, ultimately failing the UCODE_MAGIC check.

First, check for errors after the blob loop.  An error here is unrecoverable,
so avoid going around the container loop again and printing an
unhelpful-at-best error concerning bad UCODE_MAGIC.

Second, split the verify_patch_size() check out of the microcode blob header
check.  In the case that the sanity check fails, we can still use the
known-to-be-plausible header length to continue walking the container to
potentially find other applicable microcode blobs.

Before:
  (XEN) microcode: Bad microcode data
  (XEN) microcode: Wrong microcode patch file magic
  (XEN) Parsing microcode blob error -22

After:
  (XEN) microcode: Bad microcode length 0x000015c0 for cpu 0xa000
  (XEN) microcode: Bad microcode length 0x000015c0 for cpu 0xa010
  (XEN) microcode: Bad microcode length 0x000015c0 for cpu 0xa011
  (XEN) microcode: Bad microcode length 0x000015c0 for cpu 0xa200
  (XEN) microcode: Bad microcode length 0x000015c0 for cpu 0xa210
  (XEN) microcode: Bad microcode length 0x000015c0 for cpu 0xa500
  (XEN) microcode: couldn't find any matching ucode in the provided blob!

Fixes: 4de936a38a ("x86/ucode/amd: Rework parsing logic in cpu_request_microcode()")
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>