[PATCH] x86/microcode/amd: Do not overwrite final patch levels

[Borislav Petkov]

Commit 0399f73299f1b7e04de329050f7111b362b7eeb5 upstream.

A certain number of patch levels of applied microcode should not
be overwritten by the microcode loader, otherwise bad things
will happen.

Check those and abort update if the current core has one of
those final patch levels applied by the BIOS. 32-bit needs
special handling, of course.

See https://bugzilla.suse.com/show_bug.cgi?id=913996 for more
info.

Tested-by: Peter KirchgeÃner <pkirchgessner@xxxxxxxxxxx>
Signed-off-by: Borislav Petkov <bp@xxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: H. Peter Anvin <hpa@xxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Tony Luck <tony.luck@xxxxxxxxx>
Link: http://lkml.kernel.org/r/1444641762-9437-7-git-send-email-bp@xxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
 arch/x86/include/asm/microcode.h      |  2 +-
 arch/x86/kernel/cpu/microcode/amd.c       | 38 +++++++++++++++++++++++++++----
 arch/x86/kernel/cpu/microcode/amd_early.c | 13 ++++++++---
 3 files changed, 44 insertions(+), 9 deletions(-)

Index: linux/arch/x86/include/asm/microcode.h
===================================================================
--- linux.orig/arch/x86/include/asm/microcode.h	2016-05-02 13:40:48.980683909 +0200
+++ linux/arch/x86/include/asm/microcode.h	2016-05-02 13:40:48.976683909 +0200
@@ -61,5 +61,5 @@ static inline struct microcode_ops * __i
 }
 #endif
 
-extern bool check_current_patch_level(u32 *rev);
+extern bool check_current_patch_level(u32 *rev, bool early);
 #endif /* _ASM_X86_MICROCODE_H */
Index: linux/arch/x86/kernel/microcode_amd.c
===================================================================
--- linux.orig/arch/x86/kernel/microcode_amd.c	2016-05-02 13:40:48.980683909 +0200
+++ linux/arch/x86/kernel/microcode_amd.c	2016-05-02 13:56:56.688674935 +0200
@@ -124,6 +124,16 @@ static int get_matching_microcode(int cp
 }
 
 /*
+ * Those patch levels cannot be updated to newer ones and thus should be final.
+ */
+static u32 final_levels[] = {
+	0x01000098,
+	0x0100009f,
+	0x010000af,
+	0, /* T-101 terminator */
+};
+
+/*
  * Check the current patch level on this CPU.
  *
  * @rev: Use it to return the patch level. It is set to 0 in the case of
@@ -133,13 +143,33 @@ static int get_matching_microcode(int cp
  *  - true: if update should stop
  *  - false: otherwise
  */
-bool check_current_patch_level(u32 *rev)
+bool check_current_patch_level(u32 *rev, bool early)
 {
-	u32 dummy;
+	u32 lvl, dummy, i;
+	bool ret = false;
+	u32 *levels;
+
+	rdmsr(MSR_AMD64_PATCH_LEVEL, lvl, dummy);
+
+#ifdef CONFIG_X86_32
+	if (early)
+		levels = (u32 *)__pa_nodebug(&final_levels);
+	else
+#endif
+		levels = final_levels;
+
+	for (i = 0; levels[i]; i++) {
+		if (lvl == levels[i]) {
+			lvl = 0;
+			ret = true;
+			break;
+		}
+	}
 
-	rdmsr(MSR_AMD64_PATCH_LEVEL, *rev, dummy);
+	if (rev)
+		*rev = lvl;
 
-	return false;
+	return ret;
 }
 
 static int apply_microcode_amd(int cpu)
@@ -156,7 +186,7 @@ static int apply_microcode_amd(int cpu)
 	if (mc_amd == NULL)
 		return 0;
 
-	if (check_current_patch_level(&rev))
+	if (check_current_patch_level(&rev, false))
 		return -1;
 
 	wrmsrl(MSR_AMD64_PATCH_LOADER, (u64)(long)&mc_amd->hdr.data_code);

--M9NhX3UHpAaciwkO--