https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=192487
Bug ID: 192487
Summary: cpucontrol uses unsafe procedure to detect current
microcode version
Product: Base System
Version: 11.0-CURRENT
Hardware: Any
OS: Any
Status: Needs Triage
Severity: Affects Many People
Priority: ---
Component: bin
Assignee: [email protected]
Reporter: [email protected]
The Intel SDM, vol 3A, section 9.11.7.1, defines a procedure that should be
followed to ensure a valid response from the System Processor when it is
queried about the running microcode revision.
The userspace cpucontrol utility fails to follow this procedure. cpucontrol
fails to pre-init MSR 0x8B (MSR_BIOS_SIGN) with zero and issue a cpuid(1),
before it can get valid data from that same MSR.
Please refer to example 9-9 in the Intel SDM vol 3A page 9-36.
I have no idea how important this procedure is on current Intel processors, but
the impact of getting garbage from MSR_BIOS_SIGN includes either incorrectly
downgrading, or incorrectly refusing to upgrade microcode.
The bug is in file: usr.sbin/cpucontrol/intel.c
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