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Date:   Thu, 16 May 2019 16:55:33 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, Denis Kirjanov <kda@...ux-powerpc.org>,
        "Arjan van de Ven" <arjan@...ux.intel.com>,
        "Andrea Arcangeli" <aarcange@...hat.com>,
        "Josh Poimboeuf" <jpoimboe@...hat.com>,
        "Greg KH" <gregkh@...uxfoundation.org>,
        "Tom Lendacky" <thomas.lendacky@....com>,
        "Tim Chen" <tim.c.chen@...ux.intel.com>,
        "Andy Lutomirski" <luto@...nel.org>,
        "Casey Schaufler" <casey.schaufler@...el.com>,
        "Waiman Long" <longman9394@...il.com>,
        "Linus Torvalds" <torvalds@...ux-foundation.org>,
        "Jon Masters" <jcm@...hat.com>,
        "Dave Stewart" <david.c.stewart@...el.com>,
        "Asit Mallick" <asit.k.mallick@...el.com>,
        "David Woodhouse" <dwmw@...zon.co.uk>,
        "Thomas Gleixner" <tglx@...utronix.de>,
        "Kees Cook" <keescook@...omium.org>,
        "Jiri Kosina" <jkosina@...e.cz>,
        "Peter Zijlstra" <peterz@...radead.org>,
        "Dave Hansen" <dave.hansen@...el.com>,
        "Ingo Molnar" <mingo@...nel.org>, "Andi Kleen" <ak@...ux.intel.com>
Subject: [PATCH 3.16 38/86] x86/speculation: Disable STIBP when enhanced
 IBRS is in use

3.16.68-rc1 review patch.  If anyone has any objections, please let me know.

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

From: Tim Chen <tim.c.chen@...ux.intel.com>

commit 34bce7c9690b1d897686aac89604ba7adc365556 upstream.

If enhanced IBRS is active, STIBP is redundant for mitigating Spectre v2
user space exploits from hyperthread sibling.

Disable STIBP when enhanced IBRS is used.

Signed-off-by: Tim Chen <tim.c.chen@...ux.intel.com>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Reviewed-by: Ingo Molnar <mingo@...nel.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Andy Lutomirski <luto@...nel.org>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Jiri Kosina <jkosina@...e.cz>
Cc: Tom Lendacky <thomas.lendacky@....com>
Cc: Josh Poimboeuf <jpoimboe@...hat.com>
Cc: Andrea Arcangeli <aarcange@...hat.com>
Cc: David Woodhouse <dwmw@...zon.co.uk>
Cc: Andi Kleen <ak@...ux.intel.com>
Cc: Dave Hansen <dave.hansen@...el.com>
Cc: Casey Schaufler <casey.schaufler@...el.com>
Cc: Asit Mallick <asit.k.mallick@...el.com>
Cc: Arjan van de Ven <arjan@...ux.intel.com>
Cc: Jon Masters <jcm@...hat.com>
Cc: Waiman Long <longman9394@...il.com>
Cc: Greg KH <gregkh@...uxfoundation.org>
Cc: Dave Stewart <david.c.stewart@...el.com>
Cc: Kees Cook <keescook@...omium.org>
Link: https://lkml.kernel.org/r/20181125185003.966801480@linutronix.de
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 arch/x86/kernel/cpu/bugs.c | 7 +++++++
 1 file changed, 7 insertions(+)

--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -380,6 +380,10 @@ static bool stibp_needed(void)
 	if (spectre_v2_enabled == SPECTRE_V2_NONE)
 		return false;
 
+	/* Enhanced IBRS makes using STIBP unnecessary. */
+	if (spectre_v2_enabled == SPECTRE_V2_IBRS_ENHANCED)
+		return false;
+
 	if (!boot_cpu_has(X86_FEATURE_STIBP))
 		return false;
 
@@ -823,6 +827,9 @@ static void __init l1tf_select_mitigatio
 
 static char *stibp_state(void)
 {
+	if (spectre_v2_enabled == SPECTRE_V2_IBRS_ENHANCED)
+		return "";
+
 	if (x86_spec_ctrl_base & SPEC_CTRL_STIBP)
 		return ", STIBP";
 	else

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