linux-kernel - [PATCH 02/13] x86/microcode: Use own MSR accessors

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Date:   Tue, 17 Jan 2017 18:37:23 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     X86 ML <x86@...nel.org>
Cc:     LKML <linux-kernel@...r.kernel.org>
Subject: [PATCH 02/13] x86/microcode: Use own MSR accessors

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

Having tracepoints to the MSR accessors makes them unsuitable for early
microcode loading: think 32-bit before paging is enabled and us chasing
pointers to test whether a tracepoint is enabled or not. Results in a
reliable triple fault.

Thus, define microcode loader-specific MSR accessors which do the bare
minimum of reading or writing an MSR and nothing more.

Signed-off-by: Borislav Petkov <bp@...e.de>
---
 arch/x86/include/asm/microcode.h       | 29 +++++++++++++++++++++--------
 arch/x86/include/asm/microcode_intel.h |  4 ++--
 arch/x86/kernel/cpu/microcode/amd.c    |  6 +++---
 arch/x86/kernel/cpu/microcode/intel.c  |  4 ++--
 4 files changed, 28 insertions(+), 15 deletions(-)

diff --git a/arch/x86/include/asm/microcode.h b/arch/x86/include/asm/microcode.h
index 38711df3bcb5..fbecea6e46e2 100644
--- a/arch/x86/include/asm/microcode.h
+++ b/arch/x86/include/asm/microcode.h
@@ -5,20 +5,33 @@
 #include <linux/earlycpio.h>
 #include <linux/initrd.h>
 
-#define native_rdmsr(msr, val1, val2)			\
+static inline unsigned long long __rdmsr(unsigned int msr)
+{
+	DECLARE_ARGS(val, low, high);
+
+	asm volatile("1: rdmsr\n"
+		     "2:\n"
+		     : EAX_EDX_RET(val, low, high) : "c" (msr));
+	return EAX_EDX_VAL(val, low, high);
+}
+
+#define microcode_rdmsr(msr, val1, val2)		\
 do {							\
-	u64 __val = native_read_msr((msr));		\
+	u64 __val = __rdmsr((msr));			\
 	(void)((val1) = (u32)__val);			\
 	(void)((val2) = (u32)(__val >> 32));		\
 } while (0)
 
-#define native_wrmsr(msr, low, high)			\
-	native_write_msr(msr, low, high)
+static inline void microcode_wrmsr(unsigned int msr, u64 val)
+{
+	u32 low, high;
+
+	low  = (u32)val;
+	high = (u32)(val >> 32);
 
-#define native_wrmsrl(msr, val)				\
-	native_write_msr((msr),				\
-			 (u32)((u64)(val)),		\
-			 (u32)((u64)(val) >> 32))
+	asm volatile("wrmsr\n"
+		     :: "c" (msr), "a"(low), "d" (high) : "memory");
+}
 
 struct ucode_patch {
 	struct list_head plist;
diff --git a/arch/x86/include/asm/microcode_intel.h b/arch/x86/include/asm/microcode_intel.h
index e793fc9a9b20..7330b2b79484 100644
--- a/arch/x86/include/asm/microcode_intel.h
+++ b/arch/x86/include/asm/microcode_intel.h
@@ -56,13 +56,13 @@ static inline u32 intel_get_microcode_revision(void)
 {
 	u32 rev, dummy;
 
-	native_wrmsrl(MSR_IA32_UCODE_REV, 0);
+	microcode_wrmsr(MSR_IA32_UCODE_REV, 0);
 
 	/* As documented in the SDM: Do a CPUID 1 here */
 	native_cpuid_eax(1);
 
 	/* get the current revision from MSR 0x8B */
-	native_rdmsr(MSR_IA32_UCODE_REV, dummy, rev);
+	microcode_rdmsr(MSR_IA32_UCODE_REV, dummy, rev);
 
 	return rev;
 }
diff --git a/arch/x86/kernel/cpu/microcode/amd.c b/arch/x86/kernel/cpu/microcode/amd.c
index 6a31e2691f3a..3f89e6712afe 100644
--- a/arch/x86/kernel/cpu/microcode/amd.c
+++ b/arch/x86/kernel/cpu/microcode/amd.c
@@ -198,10 +198,10 @@ static int __apply_microcode_amd(struct microcode_amd *mc_amd)
 {
 	u32 rev, dummy;
 
-	native_wrmsrl(MSR_AMD64_PATCH_LOADER, (u64)(long)&mc_amd->hdr.data_code);
+	microcode_wrmsr(MSR_AMD64_PATCH_LOADER, (u64)(long)&mc_amd->hdr.data_code);
 
 	/* verify patch application was successful */
-	native_rdmsr(MSR_AMD64_PATCH_LEVEL, rev, dummy);
+	microcode_rdmsr(MSR_AMD64_PATCH_LEVEL, rev, dummy);
 	if (rev != mc_amd->hdr.patch_id)
 		return -1;
 
@@ -656,7 +656,7 @@ bool check_current_patch_level(u32 *rev, bool early)
 	bool ret = false;
 	u32 *levels;
 
-	native_rdmsr(MSR_AMD64_PATCH_LEVEL, lvl, dummy);
+	microcode_rdmsr(MSR_AMD64_PATCH_LEVEL, lvl, dummy);
 
 	if (IS_ENABLED(CONFIG_X86_32) && early)
 		levels = (u32 *)__pa_nodebug(&final_levels);
diff --git a/arch/x86/kernel/cpu/microcode/intel.c b/arch/x86/kernel/cpu/microcode/intel.c
index 8325d8a09ab0..1c6f12fa3108 100644
--- a/arch/x86/kernel/cpu/microcode/intel.c
+++ b/arch/x86/kernel/cpu/microcode/intel.c
@@ -387,7 +387,7 @@ static int collect_cpu_info_early(struct ucode_cpu_info *uci)
 
 	if ((model >= 5) || (family > 6)) {
 		/* get processor flags from MSR 0x17 */
-		native_rdmsr(MSR_IA32_PLATFORM_ID, val[0], val[1]);
+		microcode_rdmsr(MSR_IA32_PLATFORM_ID, val[0], val[1]);
 		csig.pf = 1 << ((val[1] >> 18) & 7);
 	}
 
@@ -582,7 +582,7 @@ static int apply_microcode_early(struct ucode_cpu_info *uci, bool early)
 		return 0;
 
 	/* write microcode via MSR 0x79 */
-	native_wrmsrl(MSR_IA32_UCODE_WRITE, (unsigned long)mc->bits);
+	microcode_wrmsr(MSR_IA32_UCODE_WRITE, (unsigned long)mc->bits);
 
 	rev = intel_get_microcode_revision();
 	if (rev != mc->hdr.rev)
-- 
2.11.0