[PATCH 1/2] x86, microcode: Do Intel microcode revision check signed v2

[PATCH 1/2] x86, microcode: Do Intel microcode revision check signed v2

[Andi Kleen]

From: Andi Kleen <ak@linux.intel.com>

The Intel SDM Vol 3 9.11.1 Microcode update states that
the update revision field is signed. However we do the comparison
unsigned, as the comparison gets promoted. Change the field
to be signed, so that comparision is really signed.

v2: Change field.
Signed-off-by: Andi Kleen <ak@linux.intel.com>
---
 arch/x86/include/asm/microcode_intel.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/microcode_intel.h b/arch/x86/include/asm/microcode_intel.h
index 9067166..ed1884b 100644
--- a/arch/x86/include/asm/microcode_intel.h
+++ b/arch/x86/include/asm/microcode_intel.h
@@ -5,7 +5,7 @@
 
 struct microcode_header_intel {
 	unsigned int            hdrver;
-	unsigned int            rev;
+	int	                rev;
 	unsigned int            date;
 	unsigned int            sig;
 	unsigned int            cksum;
-- 
1.8.3.1

[PATCH 2/2] x86, microcode: Add option to allow downgrading of microcode

[Andi Kleen]

From: Andi Kleen <ak@linux.intel.com>

For testing purposes it can be useful to downgrade microcode.
Normally the driver only allows upgrading.

Add a module_param (default off) that allows downgrading.

Note the module_param can currently not be set for early
ucode update, only for late.

Signed-off-by: Andi Kleen <ak@linux.intel.com>
---
 arch/x86/kernel/microcode_intel_lib.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/arch/x86/kernel/microcode_intel_lib.c b/arch/x86/kernel/microcode_intel_lib.c
index ce69320..18d5325 100644
--- a/arch/x86/kernel/microcode_intel_lib.c
+++ b/arch/x86/kernel/microcode_intel_lib.c
@@ -26,11 +26,16 @@
 #include <linux/uaccess.h>
 #include <linux/kernel.h>
 #include <linux/module.h>
+#include <linux/moduleparam.h>
 
 #include <asm/microcode_intel.h>
 #include <asm/processor.h>
 #include <asm/msr.h>
 
+static bool allow_downgrade;
+module_param(allow_downgrade, bool, 0644);
+MODULE_PARM_DESC(allow_downgrade, "Allow downgrading microcode");
+
 static inline int
 update_match_cpu(unsigned int csig, unsigned int cpf,
 		 unsigned int sig, unsigned int pf)
@@ -41,6 +46,8 @@ update_match_cpu(unsigned int csig, unsigned int cpf,
 int
 update_match_revision(struct microcode_header_intel *mc_header, int rev)
 {
+	if (allow_downgrade)
+		return 1;
 	return (mc_header->rev <= rev) ? 0 : 1;
 }
 
-- 
1.8.3.1

[PATCH 1/2] x86, microcode: Do Intel microcode revision check signed v2

[Andi Kleen]

From: Andi Kleen <ak@linux.intel.com>

The Intel SDM Vol 3 9.11.1 Microcode update states that
the update revision field is signed. However we do the comparison
unsigned, as the comparison gets promoted. Change the field
to be signed, so that comparision is really signed.

v2: Change field.
Signed-off-by: Andi Kleen <ak@linux.intel.com>
---
 arch/x86/include/asm/microcode_intel.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/microcode_intel.h b/arch/x86/include/asm/microcode_intel.h
index 9067166..ed1884b 100644
--- a/arch/x86/include/asm/microcode_intel.h
+++ b/arch/x86/include/asm/microcode_intel.h
@@ -5,7 +5,7 @@
 
 struct microcode_header_intel {
 	unsigned int            hdrver;
-	unsigned int            rev;
+	int	                rev;
 	unsigned int            date;
 	unsigned int            sig;
 	unsigned int            cksum;
-- 
1.8.3.1