From: Chen Yu <yu.c.chen@intel.com>
Date: Fri, 13 Nov 2020 09:59:23 +0800
Subject: x86/microcode/intel: Check patch signature before saving microcode
 for early loading
Git-commit: 1a371e67dc77125736cc56d3a0893f06b75855b6
Patch-mainline: v5.10-rc5
References: bsc#1112178

Currently, scan_microcode() leverages microcode_matches() to check
if the microcode matches the CPU by comparing the family and model.
However, the processor stepping and flags of the microcode signature
should also be considered when saving a microcode patch for early
update.

Use find_matching_signature() in scan_microcode() and get rid of the
now-unused microcode_matches() which is a good cleanup in itself.

Complete the verification of the patch being saved for early loading in
save_microcode_patch() directly. This needs to be done there too because
save_mc_for_early() will call save_microcode_patch() too.

The second reason why this needs to be done is because the loader still
tries to support, at least hypothetically, mixed-steppings systems and
thus adds all patches to the cache that belong to the same CPU model
albeit with different steppings.

For example:

  microcode: CPU: sig=0x906ec, pf=0x2, rev=0xd6
  microcode: mc_saved[0]: sig=0x906e9, pf=0x2a, rev=0xd6, total size=0x19400, date = 2020-04-23
  microcode: mc_saved[1]: sig=0x906ea, pf=0x22, rev=0xd6, total size=0x19000, date = 2020-04-27
  microcode: mc_saved[2]: sig=0x906eb, pf=0x2, rev=0xd6, total size=0x19400, date = 2020-04-23
  microcode: mc_saved[3]: sig=0x906ec, pf=0x22, rev=0xd6, total size=0x19000, date = 2020-04-27
  microcode: mc_saved[4]: sig=0x906ed, pf=0x22, rev=0xd6, total size=0x19400, date = 2020-04-23

The patch which is being saved for early loading, however, can only be
the one which fits the CPU this runs on so do the signature verification
before saving.

 [ bp: Do signature verification in save_microcode_patch()
       and rewrite commit message. ]

Fixes: ec400ddeff20 ("x86/microcode_intel_early.c: Early update ucode on Intel's CPU")
Signed-off-by: Chen Yu <yu.c.chen@intel.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Cc: stable@vger.kernel.org
Link: https://bugzilla.kernel.org/show_bug.cgi?id=208535
Link: https://lkml.kernel.org/r/20201113015923.13960-1-yu.c.chen@intel.com
---
 arch/x86/kernel/cpu/microcode/intel.c |   50 +---------------------------------
 1 file changed, 2 insertions(+), 48 deletions(-)

--- a/arch/x86/kernel/cpu/microcode/intel.c
+++ b/arch/x86/kernel/cpu/microcode/intel.c
@@ -103,53 +103,6 @@ static int has_newer_microcode(void *mc,
 	return find_matching_signature(mc, csig, cpf);
 }
 
-/*
- * Given CPU signature and a microcode patch, this function finds if the
- * microcode patch has matching family and model with the CPU.
- *
- * %true - if there's a match
- * %false - otherwise
- */
-static bool microcode_matches(struct microcode_header_intel *mc_header,
-			      unsigned long sig)
-{
-	unsigned long total_size = get_totalsize(mc_header);
-	unsigned long data_size = get_datasize(mc_header);
-	struct extended_sigtable *ext_header;
-	unsigned int fam_ucode, model_ucode;
-	struct extended_signature *ext_sig;
-	unsigned int fam, model;
-	int ext_sigcount, i;
-
-	fam   = x86_family(sig);
-	model = x86_model(sig);
-
-	fam_ucode   = x86_family(mc_header->sig);
-	model_ucode = x86_model(mc_header->sig);
-
-	if (fam == fam_ucode && model == model_ucode)
-		return true;
-
-	/* Look for ext. headers: */
-	if (total_size <= data_size + MC_HEADER_SIZE)
-		return false;
-
-	ext_header   = (void *) mc_header + data_size + MC_HEADER_SIZE;
-	ext_sig      = (void *)ext_header + EXT_HEADER_SIZE;
-	ext_sigcount = ext_header->count;
-
-	for (i = 0; i < ext_sigcount; i++) {
-		fam_ucode   = x86_family(ext_sig->sig);
-		model_ucode = x86_model(ext_sig->sig);
-
-		if (fam == fam_ucode && model == model_ucode)
-			return true;
-
-		ext_sig++;
-	}
-	return false;
-}
-
 static struct ucode_patch *__alloc_microcode_buf(void *data, unsigned int size)
 {
 	struct ucode_patch *p;
@@ -334,7 +287,8 @@ scan_microcode(void *data, size_t size,
 
 		size -= mc_size;
 
-		if (!microcode_matches(mc_header, uci->cpu_sig.sig)) {
+		if (!find_matching_signature(data, uci->cpu_sig.sig,
+					     uci->cpu_sig.pf)) {
 			data += mc_size;
 			continue;
 		}