[RFC 03/10] x86/speculation: Use Indirect Branch Prediction Barrier in context switch

[KarimAllah Ahmed <karahmed@amazon.de>]

From: Thomas Gleixner <tglx@linutronix.de>

[peterz: comment]

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
---
 arch/x86/mm/tlb.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/arch/x86/mm/tlb.c b/arch/x86/mm/tlb.c
index a156195..304de7d 100644
--- a/arch/x86/mm/tlb.c
+++ b/arch/x86/mm/tlb.c
@@ -6,13 +6,14 @@
 #include <linux/interrupt.h>
 #include <linux/export.h>
 #include <linux/cpu.h>
+#include <linux/debugfs.h>
 
 #include <asm/tlbflush.h>
 #include <asm/mmu_context.h>
+#include <asm/nospec-branch.h>
 #include <asm/cache.h>
 #include <asm/apic.h>
 #include <asm/uv/uv.h>
-#include <linux/debugfs.h>
 
 /*
  *	TLB flushing, formerly SMP-only
@@ -220,6 +221,13 @@ void switch_mm_irqs_off(struct mm_struct *prev, struct mm_struct *next,
 		u16 new_asid;
 		bool need_flush;
 
+		/*
+		 * Avoid user/user BTB poisoning by flushing the branch predictor
+		 * when switching between processes. This stops one process from
+		 * doing Spectre-v2 attacks on another.
+		 */
+		indirect_branch_prediction_barrier();
+
 		if (IS_ENABLED(CONFIG_VMAP_STACK)) {
 			/*
 			 * If our current stack is in vmalloc space and isn't
-- 
2.7.4