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From:   David Woodhouse <dwmw@amazon.co.uk>
To:     arjan@linux.intel.com, tglx@linutronix.de, karahmed@amazon.de,
        x86@kernel.org, linux-kernel@vger.kernel.org,
        tim.c.chen@linux.intel.com, bp@alien8.de, peterz@infradead.org,
        pbonzini@redhat.com, ak@linux.intel.com,
        torvalds@linux-foundation.org, gregkh@linux-foundation.org,
        dave.hansen@intel.com
Subject: [PATCH 1/3] x86/cpufeatures: Clean up Spectre v2 related CPUID flags
Date:   Sat, 27 Jan 2018 16:24:32 +0000
Message-Id: <1517070274-12128-2-git-send-email-dwmw@amazon.co.uk>
In-Reply-To: <1517070274-12128-1-git-send-email-dwmw@amazon.co.uk>
References: <1517070274-12128-1-git-send-email-dwmw@amazon.co.uk>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

We want to expose the hardware features simply in /proc/cpuinfo as "ibrs",
"ibpb" and "stibp". Since AMD gives us separate CPUID bits for those, use
them as the user-visible bits.

When the Intel SPEC_CTRL bit is set which indicates both IBRS and IBPB
capability, set those (AMD) bits accordingly. Likewise if the Intel STIBP
bit is set, set the AMD STIBP but that we're using for the generic hardware
capability.

Hide the rest from /proc/cpuinfo by putting "" in the comments. Including
RETPOLINE and RETPOLINE_AMD which shouldn't be visible there. There are
patches to make the sysfs vulnerabilities information non-readable by
root, and the same should apply to all information about which mitigations
are actually in use. Those *shouldn't* appear in /proc/cpuinfo.

The feature bit for whether we're actually *using* IBPB, which we need
like PTI does just because we're using it for ALTERNATIVEs, is renamed
to X86_FEATURE_USE_IBPB.

Based on patches from Borislav Petkov <bp@suse.de>
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
---
 arch/x86/include/asm/cpufeatures.h   | 18 +++++++++---------
 arch/x86/include/asm/nospec-branch.h |  2 +-
 arch/x86/kernel/cpu/bugs.c           |  5 ++---
 arch/x86/kernel/cpu/intel.c          | 31 +++++++++++++++++++++----------
 4 files changed, 33 insertions(+), 23 deletions(-)

diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
index 07934b2..73b5fff 100644
--- a/arch/x86/include/asm/cpufeatures.h
+++ b/arch/x86/include/asm/cpufeatures.h
@@ -203,14 +203,14 @@
 #define X86_FEATURE_PROC_FEEDBACK	( 7*32+ 9) /* AMD ProcFeedbackInterface */
 #define X86_FEATURE_SME			( 7*32+10) /* AMD Secure Memory Encryption */
 #define X86_FEATURE_PTI			( 7*32+11) /* Kernel Page Table Isolation enabled */
-#define X86_FEATURE_RETPOLINE		( 7*32+12) /* Generic Retpoline mitigation for Spectre variant 2 */
-#define X86_FEATURE_RETPOLINE_AMD	( 7*32+13) /* AMD Retpoline mitigation for Spectre variant 2 */
+#define X86_FEATURE_RETPOLINE		( 7*32+12) /* "" Generic Retpoline mitigation for Spectre variant 2 */
+#define X86_FEATURE_RETPOLINE_AMD	( 7*32+13) /* "" AMD Retpoline mitigation for Spectre variant 2 */
 #define X86_FEATURE_INTEL_PPIN		( 7*32+14) /* Intel Processor Inventory Number */
 
 #define X86_FEATURE_MBA			( 7*32+18) /* Memory Bandwidth Allocation */
-#define X86_FEATURE_RSB_CTXSW		( 7*32+19) /* Fill RSB on context switches */
+#define X86_FEATURE_RSB_CTXSW		( 7*32+19) /* "" Fill RSB on context switches */
 
-#define X86_FEATURE_IBPB		( 7*32+21) /* Indirect Branch Prediction Barrier enabled*/
+#define X86_FEATURE_USE_IBPB		( 7*32+21) /* "" Indirect Branch Prediction Barrier enabled */
 
 /* Virtualization flags: Linux defined, word 8 */
 #define X86_FEATURE_TPR_SHADOW		( 8*32+ 0) /* Intel TPR Shadow */
@@ -271,9 +271,9 @@
 #define X86_FEATURE_CLZERO		(13*32+ 0) /* CLZERO instruction */
 #define X86_FEATURE_IRPERF		(13*32+ 1) /* Instructions Retired Count */
 #define X86_FEATURE_XSAVEERPTR		(13*32+ 2) /* Always save/restore FP error pointers */
-#define X86_FEATURE_AMD_PRED_CMD	(13*32+12) /* Prediction Command MSR (AMD) */
-#define X86_FEATURE_AMD_SPEC_CTRL	(13*32+14) /* Speculation Control MSR only (AMD) */
-#define X86_FEATURE_AMD_STIBP		(13*32+15) /* Single Thread Indirect Branch Predictors (AMD) */
+#define X86_FEATURE_IBPB		(13*32+12) /* Indirect Branch Prediction Barrier */
+#define X86_FEATURE_IBRS		(13*32+14) /* Indirect Branch Restricted Speculation */
+#define X86_FEATURE_STIBP		(13*32+15) /* Single Thread Indirect Branch Predictors */
 
 /* Thermal and Power Management Leaf, CPUID level 0x00000006 (EAX), word 14 */
 #define X86_FEATURE_DTHERM		(14*32+ 0) /* Digital Thermal Sensor */
@@ -325,8 +325,8 @@
 /* Intel-defined CPU features, CPUID level 0x00000007:0 (EDX), word 18 */
 #define X86_FEATURE_AVX512_4VNNIW	(18*32+ 2) /* AVX-512 Neural Network Instructions */
 #define X86_FEATURE_AVX512_4FMAPS	(18*32+ 3) /* AVX-512 Multiply Accumulation Single precision */
-#define X86_FEATURE_SPEC_CTRL		(18*32+26) /* Speculation Control (IBRS + IBPB) */
-#define X86_FEATURE_STIBP		(18*32+27) /* Single Thread Indirect Branch Predictors */
+#define X86_FEATURE_SPEC_CTRL		(18*32+26) /* "" Speculation Control (IBRS + IBPB) */
+#define X86_FEATURE_INTEL_STIBP		(18*32+27) /* "" Single Thread Indirect Branch Predictors */
 #define X86_FEATURE_ARCH_CAPABILITIES	(18*32+29) /* IA32_ARCH_CAPABILITIES MSR (Intel) */
 
 /*
diff --git a/arch/x86/include/asm/nospec-branch.h b/arch/x86/include/asm/nospec-branch.h
index 865192a..19ecb54 100644
--- a/arch/x86/include/asm/nospec-branch.h
+++ b/arch/x86/include/asm/nospec-branch.h
@@ -225,7 +225,7 @@ static inline void indirect_branch_prediction_barrier(void)
 				 "movl %[val], %%eax\n\t"
 				 "movl $0, %%edx\n\t"
 				 "wrmsr",
-				 X86_FEATURE_IBPB)
+				 X86_FEATURE_USE_IBPB)
 		     : : [msr] "i" (MSR_IA32_PRED_CMD),
 			 [val] "i" (PRED_CMD_IBPB)
 		     : "eax", "ecx", "edx", "memory");
diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index c988a8a..0c6dd43 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -265,9 +265,8 @@ static void __init spectre_v2_select_mitigation(void)
 	}
 
 	/* Initialize Indirect Branch Prediction Barrier if supported */
-	if (boot_cpu_has(X86_FEATURE_SPEC_CTRL) ||
-	    boot_cpu_has(X86_FEATURE_AMD_PRED_CMD)) {
-		setup_force_cpu_cap(X86_FEATURE_IBPB);
+	if (boot_cpu_has(X86_FEATURE_IBPB)) {
+		setup_force_cpu_cap(X86_FEATURE_USE_IBPB);
 		pr_info("Enabling Indirect Branch Prediction Barrier\n");
 	}
 }
diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c
index 5faa487..0c8b916 100644
--- a/arch/x86/kernel/cpu/intel.c
+++ b/arch/x86/kernel/cpu/intel.c
@@ -175,17 +175,28 @@ static void early_init_intel(struct cpuinfo_x86 *c)
 	if (c->x86 >= 6 && !cpu_has(c, X86_FEATURE_IA64))
 		c->microcode = intel_get_microcode_revision();
 
-	if ((cpu_has(c, X86_FEATURE_SPEC_CTRL) ||
-	     cpu_has(c, X86_FEATURE_STIBP) ||
-	     cpu_has(c, X86_FEATURE_AMD_SPEC_CTRL) ||
-	     cpu_has(c, X86_FEATURE_AMD_PRED_CMD) ||
-	     cpu_has(c, X86_FEATURE_AMD_STIBP)) && bad_spectre_microcode(c)) {
-		pr_warn("Intel Spectre v2 broken microcode detected; disabling SPEC_CTRL\n");
-		clear_cpu_cap(c, X86_FEATURE_SPEC_CTRL);
+	/*
+	 * The Intel SPEC_CTRL CPUID bit implies IBRS and IBPB support,
+	 * and they also have a different bit for STIBP support. Also,
+	 * a hypervisor might have set the individual AMD bits even on
+	 * Intel CPUs, for finer-grained selection of what's available.
+	 */
+	if (cpu_has(c, X86_FEATURE_SPEC_CTRL)) {
+		set_cpu_cap(c, X86_FEATURE_IBRS);
+		set_cpu_cap(c, X86_FEATURE_IBPB);
+	}
+	if (cpu_has(c, X86_FEATURE_INTEL_STIBP))
+		set_cpu_cap(c, X86_FEATURE_STIBP);
+
+	/* Now if any of them are set, check the blacklist and clear the lot */
+	if ((cpu_has(c, X86_FEATURE_IBRS) || cpu_has(c, X86_FEATURE_IBPB) ||
+	     cpu_has(c, X86_FEATURE_STIBP)) && bad_spectre_microcode(c)) {
+		pr_warn("Intel Spectre v2 broken microcode detected; disabling Speculation Control\n");
+		clear_cpu_cap(c, X86_FEATURE_IBRS);
+		clear_cpu_cap(c, X86_FEATURE_IBPB);
 		clear_cpu_cap(c, X86_FEATURE_STIBP);
-		clear_cpu_cap(c, X86_FEATURE_AMD_SPEC_CTRL);
-		clear_cpu_cap(c, X86_FEATURE_AMD_PRED_CMD);
-		clear_cpu_cap(c, X86_FEATURE_AMD_STIBP);
+		clear_cpu_cap(c, X86_FEATURE_SPEC_CTRL);
+		clear_cpu_cap(c, X86_FEATURE_INTEL_STIBP);
 	}
 
 	/*
-- 
2.7.4