linux-kernel - [PATCH 4.15 17/60] x86/speculation: Simplify indirect_branch_prediction

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Date:   Mon,  5 Feb 2018 10:22:50 -0800
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Borislav Petkov <bp@...e.de>,
        David Woodhouse <dwmw@...zon.co.uk>,
        Thomas Gleixner <tglx@...utronix.de>, ak@...ux.intel.com,
        dave.hansen@...el.com, karahmed@...zon.de, arjan@...ux.intel.com,
        torvalds@...ux-foundation.org, peterz@...radead.org, bp@...en8.de,
        pbonzini@...hat.com, tim.c.chen@...ux.intel.com,
        gregkh@...ux-foundation.org
Subject: [PATCH 4.15 17/60] x86/speculation: Simplify indirect_branch_prediction_barrier()

4.15-stable review patch.  If anyone has any objections, please let me know.

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

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

commit 64e16720ea0879f8ab4547e3b9758936d483909b

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
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>


---
 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(-)

--- 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__ */
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -971,4 +971,7 @@ 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 */
--- 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 devic
 		       spectre_v2_module_string());
 }
 #endif
+
+void __ibp_barrier(void)
+{
+	__wrmsr(MSR_IA32_PRED_CMD, PRED_CMD_IBPB, 0);
+}
+EXPORT_SYMBOL_GPL(__ibp_barrier);