From aa1b136ff1798a2c1a81270ccd20e7252e30ff1f Mon Sep 17 00:00:00 2001 From: Andrew Cooper Date: Mon, 26 Oct 2020 15:27:35 +0000 Subject: [PATCH] x86/ucode/intel: Fix handling of microcode revision For Intel microcode blobs, the revision field is signed (as documented in the SDM) and negative revisions are used for pre-production/test microcode (not documented publicly anywhere I can spot). Adjust the revision checking to match the algorithm presented here: https://software.intel.com/security-software-guidance/best-practices/microcode-update-guidance This treats pre-production microcode as always applicable, but also production microcode having higher precedent than pre-production. It is expected that anyone using pre-production microcode knows what they are doing. This is necessary to load production microcode on an SDP with pre-production microcode embedded in firmware. Signed-off-by: Andrew Cooper Reviewed-by: Jan Beulich --- xen/arch/x86/cpu/microcode/intel.c | 15 +++++++++++++-- 1 file changed, 13 insertions(+), 2 deletions(-) diff --git a/xen/arch/x86/cpu/microcode/intel.c b/xen/arch/x86/cpu/microcode/intel.c index e1ccb5d232..5fa2821cdb 100644 --- a/xen/arch/x86/cpu/microcode/intel.c +++ b/xen/arch/x86/cpu/microcode/intel.c @@ -33,7 +33,7 @@ struct microcode_patch { uint32_t hdrver; - uint32_t rev; + int32_t rev; uint16_t year; uint8_t day; uint8_t month; @@ -222,12 +222,23 @@ static int microcode_sanity_check(const struct microcode_patch *patch) return 0; } +/* + * Production microcode has a positive revision. Pre-production microcode has + * a negative revision. + */ static enum microcode_match_result compare_revisions( - uint32_t old_rev, uint32_t new_rev) + int32_t old_rev, int32_t new_rev) { if ( new_rev > old_rev ) return NEW_UCODE; + /* + * Treat pre-production as always applicable - anyone using pre-production + * microcode knows what they are doing, and can keep any resulting pieces. + */ + if ( new_rev < 0 ) + return NEW_UCODE; + return OLD_UCODE; } -- 2.39.5