From mboxrd@z Thu Jan  1 00:00:00 1970
From: KarimAllah Ahmed <karahmed@amazon.de>
Subject: [RFC 03/10] x86/speculation: Use Indirect Branch Prediction Barrier in context switch
Date: Sat, 20 Jan 2018 20:22:54 +0100
Message-ID: <1516476182-5153-4-git-send-email-karahmed@amazon.de>
References: <1516476182-5153-1-git-send-email-karahmed@amazon.de>
Cc: KarimAllah Ahmed <karahmed@amazon.de>,
        Andi Kleen <ak@linux.intel.com>,
        Andrea Arcangeli <aarcange@redhat.com>,
        Andy Lutomirski <luto@kernel.org>,
        Arjan van de Ven <arjan@linux.intel.com>,
        Ashok Raj <ashok.raj@intel.com>,
        Asit Mallick <asit.k.mallick@intel.com>,
        Borislav Petkov <bp@suse.de>,
        Dan Williams <dan.j.williams@intel.com>,
        Dave Hansen <dave.hansen@intel.com>,
        David Woodhouse <dwmw@amazon.co.uk>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        "H . Peter Anvin" <hpa@zytor.com>, Ingo Molnar <mingo@redhat.com>,
        Janakarajan Natarajan <Janakarajan.Natarajan@amd.com>,
        Joerg Roedel <joro@8bytes.org>,
        Jun Nakajima <jun.nakajima@intel.com>,
        Laura Abbott <labbott@redhat.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Masami Hiramatsu <m
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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