Patch "x86/speculation: Simplify indirect_branch_prediction_barrier()" has been added to the 4.15-stable tree

This is a note to let you know that I've just added the patch titled

x86/speculation: Simplify indirect_branch_prediction_barrier()

to the 4.15-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
x86speculation_Simplify_indirect_branch_prediction_barrier().patch
and it can be found in the queue-4.15 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

Subject: x86/speculation: Simplify indirect_branch_prediction_barrier()
From: Borislav Petkov [email protected]
Date: Sat Jan 27 16:24:34 2018 +0000

From: Borislav Petkov [email protected]

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]

---
 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(-)

@@ -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__ */

@@ -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 */

@@ -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);

Patches currently in stable-queue which might be from [email protected] are

queue-4.15/x86pti_Do_not_enable_PTI_on_CPUs_which_are_not_vulnerable_to_Meltdown.patch queue-4.15/x86cpufeatures_Add_Intel_feature_bits_for_Speculation_Control.patch queue-4.15/x86alternative_Print_unadorned_pointers.patch queue-4.15/x86cpufeatures_Add_CPUID_7_EDX_CPUID_leaf.patch queue-4.15/x86bugs_Drop_one_mitigation_from_dmesg.patch queue-4.15/x86speculation_Simplify_indirect_branch_prediction_barrier().patch queue-4.15/x86nospec_Fix_header_guards_names.patch queue-4.15/x86retpoline_Simplify_vmexit_fill_RSB().patch queue-4.15/x86cpufeatures_Clean_up_Spectre_v2_related_CPUID_flags.patch