linux-kernel - [PATCH 3.16 047/410] x86/speculation: Add basic IBPB (Indirect Branch Prediction Barrier) support

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Date:   Thu, 07 Jun 2018 15:05:21 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org,
        "Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
        pbonzini@...hat.com, tim.c.chen@...ux.intel.com,
        peterz@...radead.org, ashok.raj@...el.com,
        "David Woodhouse" <dwmw@...zon.co.uk>, bp@...en8.de,
        ak@...ux.intel.com, gregkh@...ux-foundation.org,
        dave.hansen@...el.com, "KarimAllah Ahmed" <karahmed@...zon.de>,
        torvalds@...ux-foundation.org, arjan@...ux.intel.com,
        gnomes@...rguk.ukuu.org.uk
Subject: [PATCH 3.16 047/410] x86/speculation: Add basic IBPB (Indirect
 Branch Prediction Barrier)  support

3.16.57-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: David Woodhouse <dwmw@...zon.co.uk>

commit 20ffa1caecca4db8f79fe665acdeaa5af815a24d upstream.

Expose indirect_branch_prediction_barrier() for use in subsequent patches.

[ tglx: Add IBPB status to spectre_v2 sysfs file ]

Co-developed-by: KarimAllah Ahmed <karahmed@...zon.de>
Signed-off-by: KarimAllah Ahmed <karahmed@...zon.de>
Signed-off-by: David Woodhouse <dwmw@...zon.co.uk>
Cc: gnomes@...rguk.ukuu.org.uk
Cc: ak@...ux.intel.com
Cc: ashok.raj@...el.com
Cc: dave.hansen@...el.com
Cc: arjan@...ux.intel.com
Cc: torvalds@...ux-foundation.org
Cc: peterz@...radead.org
Cc: bp@...en8.de
Cc: pbonzini@...hat.com
Cc: tim.c.chen@...ux.intel.com
Cc: gregkh@...ux-foundation.org
Link: https://lkml.kernel.org/r/1516896855-7642-8-git-send-email-dwmw@amazon.co.uk
Signed-off-by: David Woodhouse <dwmw@...zon.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
[bwh: Backported to 3.16:
 - Renumber the feature bit
 - Adjust context]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 arch/x86/include/asm/cpufeature.h    |  2 ++
 arch/x86/include/asm/nospec-branch.h | 13 +++++++++++++
 arch/x86/kernel/cpu/bugs.c           | 10 +++++++++-
 3 files changed, 24 insertions(+), 1 deletion(-)

--- a/arch/x86/include/asm/cpufeature.h
+++ b/arch/x86/include/asm/cpufeature.h
@@ -189,6 +189,8 @@
 #define X86_FEATURE_INVPCID_SINGLE (7*32+10) /* Effectively INVPCID && CR4.PCIDE=1 */
 #define X86_FEATURE_RSB_CTXSW	(7*32+11) /* "" Fill RSB on context switches */
 
+#define X86_FEATURE_IBPB	(7*32+12) /* Indirect Branch Prediction Barrier enabled*/
+
 #define X86_FEATURE_RETPOLINE	(7*32+29) /* "" Generic Retpoline mitigation for Spectre variant 2 */
 #define X86_FEATURE_RETPOLINE_AMD (7*32+30) /* "" AMD Retpoline mitigation for Spectre variant 2 */
 /* Because the ALTERNATIVE scheme is for members of the X86_FEATURE club... */
--- a/arch/x86/include/asm/nospec-branch.h
+++ b/arch/x86/include/asm/nospec-branch.h
@@ -194,5 +194,18 @@ static inline void vmexit_fill_RSB(void)
 #endif
 }
 
+static inline void indirect_branch_prediction_barrier(void)
+{
+	asm volatile(ALTERNATIVE("",
+				 "movl %[msr], %%ecx\n\t"
+				 "movl %[val], %%eax\n\t"
+				 "movl $0, %%edx\n\t"
+				 "wrmsr",
+				 X86_FEATURE_IBPB)
+		     : : [msr] "i" (MSR_IA32_PRED_CMD),
+			 [val] "i" (PRED_CMD_IBPB)
+		     : "eax", "ecx", "edx", "memory");
+}
+
 #endif /* __ASSEMBLY__ */
 #endif /* _ASM_X86_NOSPEC_BRANCH_H_ */
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -358,6 +358,13 @@ retpoline_auto:
 		setup_force_cpu_cap(X86_FEATURE_RSB_CTXSW);
 		pr_info("Filling RSB on context switch\n");
 	}
+
+	/* 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);
+		pr_info("Enabling Indirect Branch Prediction Barrier\n");
+	}
 }
 
 #undef pr_fmt
@@ -387,7 +394,8 @@ ssize_t cpu_show_spectre_v2(struct devic
 	if (!boot_cpu_has_bug(X86_BUG_SPECTRE_V2))
 		return sprintf(buf, "Not affected\n");
 
-	return sprintf(buf, "%s%s\n", spectre_v2_strings[spectre_v2_enabled],
+	return sprintf(buf, "%s%s%s\n", spectre_v2_strings[spectre_v2_enabled],
+		       boot_cpu_has(X86_FEATURE_IBPB) ? ", IPBP" : "",
 		       spectre_v2_module_string());
 }
 #endif