linux-kernel - [tip:x86/pti] x86/speculation: Simplify indirect_branch_prediction

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Message-ID: <tip-64e16720ea0879f8ab4547e3b9758936d483909b@git.kernel.org>
Date:   Sat, 27 Jan 2018 10:17:02 -0800
From:   tip-bot for Borislav Petkov <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, dwmw@...zon.co.uk, hpa@...or.com,
        tglx@...utronix.de, bp@...e.de, mingo@...nel.org
Subject: [tip:x86/pti] x86/speculation: Simplify
 indirect_branch_prediction_barrier()

Commit-ID:  64e16720ea0879f8ab4547e3b9758936d483909b
Gitweb:     https://git.kernel.org/tip/64e16720ea0879f8ab4547e3b9758936d483909b
Author:     Borislav Petkov <bp@...e.de>
AuthorDate: Sat, 27 Jan 2018 16:24:34 +0000
Committer:  Thomas Gleixner <tglx@...utronix.de>
CommitDate: Sat, 27 Jan 2018 19:10:45 +0100

x86/speculation: Simplify indirect_branch_prediction_barrier()

Make it all a function which does the WRMSR instead of having a hairy
inline asm.

[dwmw2: export it, fix CONFIG_RETPOLINE issues]

Signed-off-by: Borislav Petkov <bp@...e.de>
Signed-off-by: David Woodhouse <dwmw@...zon.co.uk>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Cc: ak@...ux.intel.com
Cc: dave.hansen@...el.com
Cc: karahmed@...zon.de
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/1517070274-12128-4-git-send-email-dwmw@amazon.co.uk

---
 arch/x86/include/asm/nospec-branch.h | 13 ++++---------
 arch/x86/include/asm/processor.h     |  3 +++
 arch/x86/kernel/cpu/bugs.c           |  6 ++++++
 3 files changed, 13 insertions(+), 9 deletions(-)

diff --git a/arch/x86/include/asm/nospec-branch.h b/arch/x86/include/asm/nospec-branch.h
index df4ececa..d15d471 100644
--- a/arch/x86/include/asm/nospec-branch.h
+++ b/arch/x86/include/asm/nospec-branch.h
@@ -164,15 +164,10 @@ static inline void vmexit_fill_RSB(void)
 
 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_USE_IBPB)
-		     : : [msr] "i" (MSR_IA32_PRED_CMD),
-			 [val] "i" (PRED_CMD_IBPB)
-		     : "eax", "ecx", "edx", "memory");
+	alternative_input("",
+			  "call __ibp_barrier",
+			  X86_FEATURE_USE_IBPB,
+			  ASM_NO_INPUT_CLOBBER("eax", "ecx", "edx", "memory"));
 }
 
 #endif /* __ASSEMBLY__ */
diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index 9c18da6..881ca3b 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -970,4 +970,7 @@ bool xen_set_default_idle(void);
 
 void stop_this_cpu(void *dummy);
 void df_debug(struct pt_regs *regs, long error_code);
+
+void __ibp_barrier(void);
+
 #endif /* _ASM_X86_PROCESSOR_H */
diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index 32d8e6c..3bfb2b2 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -311,3 +311,9 @@ ssize_t cpu_show_spectre_v2(struct device *dev,
 		       spectre_v2_module_string());
 }
 #endif
+
+void __ibp_barrier(void)
+{
+	__wrmsr(MSR_IA32_PRED_CMD, PRED_CMD_IBPB, 0);
+}
+EXPORT_SYMBOL_GPL(__ibp_barrier);