x86/microcode/AMD: Limit Entrysign signature checking to known generations

Limit Entrysign sha256 signature checking to CPUs in the range Zen1-Zen5.

X86_BUG cannot be used here because the loading on the BSP happens way
too early, before the cpufeatures machinery has been set up.

Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://patch.msgid.link/all/20251023124629.5385-1-bp@kernel.org

Author: bp3tk0v

arch/x86/kernel/cpu/microcode/amd.c

@@ -233,13 +233,31 @@ static bool need_sha_check(u32 cur_rev)
 	return true;
 }
 
+static bool cpu_has_entrysign(void)
+{
+	unsigned int fam   = x86_family(bsp_cpuid_1_eax);
+	unsigned int model = x86_model(bsp_cpuid_1_eax);
+
+	if (fam == 0x17 || fam == 0x19)
+		return true;
+
+	if (fam == 0x1a) {
+		if (model <= 0x2f ||
+		    (0x40 <= model && model <= 0x4f) ||
+		    (0x60 <= model && model <= 0x6f))
+			return true;
+	}
+
+	return false;
+}
+
 static bool verify_sha256_digest(u32 patch_id, u32 cur_rev, const u8 *data, unsigned int len)
 {
 	struct patch_digest *pd = NULL;
 	u8 digest[SHA256_DIGEST_SIZE];
 	int i;
 
-	if (x86_family(bsp_cpuid_1_eax) < 0x17)
+	if (!cpu_has_entrysign())
 		return true;
 
 	if (!need_sha_check(cur_rev))