linux-kernel - [PATCH] x86/microcode: Do the family check first

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Message-Id: <20171012112316.977-1-bp@alien8.de>
Date:   Thu, 12 Oct 2017 13:23:16 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     X86 ML <x86@...nel.org>
Cc:     LKML <linux-kernel@...r.kernel.org>
Subject: [PATCH] x86/microcode: Do the family check first

From: Borislav Petkov <bp@...e.de>

On CPUs like AMD's Geode, for example, we shouldn't even try to load
microcode because they do not support the modern microcode loading
interface.

However, we do the family check *after* the other checks whether the
loader has been disabled on the command line or whether we're running in
a guest.

So move the family checks first in order to exit early if we're being
loaded on an unsupported family.

Reported-and-tested-by: Sven Glodowski <glodi1@...or.de>
Signed-off-by: Borislav Petkov <bp@...e.de>
Cc: <stable@...r.kernel.org> # 4.11..
Link: http://bugzilla.suse.com/show_bug.cgi?id=1061396
---
 arch/x86/kernel/cpu/microcode/core.c | 27 ++++++++++++++++++---------
 1 file changed, 18 insertions(+), 9 deletions(-)

diff --git a/arch/x86/kernel/cpu/microcode/core.c b/arch/x86/kernel/cpu/microcode/core.c
index 86e8f0b2537b..c4fa4a85d4cb 100644
--- a/arch/x86/kernel/cpu/microcode/core.c
+++ b/arch/x86/kernel/cpu/microcode/core.c
@@ -122,9 +122,6 @@ static bool __init check_loader_disabled_bsp(void)
 	bool *res = &dis_ucode_ldr;
 #endif
 
-	if (!have_cpuid_p())
-		return *res;
-
 	/*
 	 * CPUID(1).ECX[31]: reserved for hypervisor use. This is still not
 	 * completely accurate as xen pv guests don't see that CPUID bit set but
@@ -166,24 +163,36 @@ bool get_builtin_firmware(struct cpio_data *cd, const char *name)
 void __init load_ucode_bsp(void)
 {
 	unsigned int cpuid_1_eax;
+	bool intel = true;
 
-	if (check_loader_disabled_bsp())
+	if (!have_cpuid_p())
 		return;
 
 	cpuid_1_eax = native_cpuid_eax(1);
 
 	switch (x86_cpuid_vendor()) {
 	case X86_VENDOR_INTEL:
-		if (x86_family(cpuid_1_eax) >= 6)
-			load_ucode_intel_bsp();
+		if (x86_family(cpuid_1_eax) < 6)
+			return;
 		break;
+
 	case X86_VENDOR_AMD:
-		if (x86_family(cpuid_1_eax) >= 0x10)
-			load_ucode_amd_bsp(cpuid_1_eax);
+		if (x86_family(cpuid_1_eax) < 0x10)
+			return;
+		intel = false;
 		break;
+
 	default:
-		break;
+		return;
 	}
+
+	if (check_loader_disabled_bsp())
+		return;
+
+	if (intel)
+		load_ucode_intel_bsp();
+	else
+		load_ucode_amd_bsp(cpuid_1_eax);
 }
 
 static bool check_loader_disabled_ap(void)
-- 
2.13.0