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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>,
        "Thomas Gleixner" <tglx@...utronix.de>,
        "Catalin Marinas" <catalin.marinas@....com>,
        "Borislav Petkov" <bp@...en8.de>, "Jiri Kosina" <jkosina@...e.cz>,
        "Tyler Hicks" <tyhicks@...onical.com>,
        "Peter Zijlstra" <peterz@...radead.org>,
        "Paul Mackerras" <paulus@...ba.org>,
        "Randy Dunlap" <rdunlap@...radead.org>,
        "Michael Ellerman" <mpe@...erman.id.au>,
        "Jiri Kosina" <jikos@...nel.org>,
        "Waiman Long" <longman@...hat.com>,
        "Steven Price" <steven.price@....com>, linux-s390@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linuxppc-dev@...ts.ozlabs.org,
        "Heiko Carstens" <heiko.carstens@...ibm.com>,
        "Andrea Arcangeli" <aarcange@...hat.com>,
        linux-arch@...r.kernel.org,
        "Benjamin Herrenschmidt" <benh@...nel.crashing.org>,
        "Will Deacon" <will.deacon@....com>,
        "Phil Auld" <pauld@...hat.com>,
        "Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
        "H . Peter Anvin" <hpa@...or.com>,
        "Josh Poimboeuf" <jpoimboe@...hat.com>,
        "Jon Masters" <jcm@...hat.com>,
        "Linus Torvalds" <torvalds@...ux-foundation.org>,
        "Andy Lutomirski" <luto@...nel.org>,
        "Martin Schwidefsky" <schwidefsky@...ibm.com>
Subject: [PATCH 3.16 80/86] x86/speculation: Support 'mitigations='
 cmdline option

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

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

From: Josh Poimboeuf <jpoimboe@...hat.com>

commit d68be4c4d31295ff6ae34a8ddfaa4c1a8ff42812 upstream.

Configure x86 runtime CPU speculation bug mitigations in accordance with
the 'mitigations=' cmdline option.  This affects Meltdown, Spectre v2,
Speculative Store Bypass, and L1TF.

The default behavior is unchanged.

Signed-off-by: Josh Poimboeuf <jpoimboe@...hat.com>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Tested-by: Jiri Kosina <jkosina@...e.cz> (on x86)
Reviewed-by: Jiri Kosina <jkosina@...e.cz>
Cc: Borislav Petkov <bp@...en8.de>
Cc: "H . Peter Anvin" <hpa@...or.com>
Cc: Andy Lutomirski <luto@...nel.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Jiri Kosina <jikos@...nel.org>
Cc: Waiman Long <longman@...hat.com>
Cc: Andrea Arcangeli <aarcange@...hat.com>
Cc: Jon Masters <jcm@...hat.com>
Cc: Benjamin Herrenschmidt <benh@...nel.crashing.org>
Cc: Paul Mackerras <paulus@...ba.org>
Cc: Michael Ellerman <mpe@...erman.id.au>
Cc: linuxppc-dev@...ts.ozlabs.org
Cc: Martin Schwidefsky <schwidefsky@...ibm.com>
Cc: Heiko Carstens <heiko.carstens@...ibm.com>
Cc: linux-s390@...r.kernel.org
Cc: Catalin Marinas <catalin.marinas@....com>
Cc: Will Deacon <will.deacon@....com>
Cc: linux-arm-kernel@...ts.infradead.org
Cc: linux-arch@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: Tyler Hicks <tyhicks@...onical.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Randy Dunlap <rdunlap@...radead.org>
Cc: Steven Price <steven.price@....com>
Cc: Phil Auld <pauld@...hat.com>
Link: https://lkml.kernel.org/r/6616d0ae169308516cfdf5216bedd169f8a8291b.1555085500.git.jpoimboe@redhat.com
[bwh: Backported to 3.16:
 - Drop the auto,nosmt option and the l1tf mitigation selection, which we can't
   support
 - Adjust filenames, context]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -1907,15 +1907,19 @@ bytes respectively. Such letter suffixes
 			http://repo.or.cz/w/linux-2.6/mini2440.git
 
 	mitigations=
-			Control optional mitigations for CPU vulnerabilities.
-			This is a set of curated, arch-independent options, each
-			of which is an aggregation of existing arch-specific
-			options.
+			[X86] Control optional mitigations for CPU
+			vulnerabilities.  This is a set of curated,
+			arch-independent options, each of which is an
+			aggregation of existing arch-specific options.
 
 			off
 				Disable all optional CPU mitigations.  This
 				improves system performance, but it may also
 				expose users to several CPU vulnerabilities.
+				Equivalent to: nopti [X86]
+					       nospectre_v2 [X86]
+					       spectre_v2_user=off [X86]
+					       spec_store_bypass_disable=off [X86]
 
 			auto (default)
 				Mitigate all CPU vulnerabilities, but leave SMT
@@ -1923,7 +1927,7 @@ bytes respectively. Such letter suffixes
 				users who don't want to be surprised by SMT
 				getting disabled across kernel upgrades, or who
 				have other ways of avoiding SMT-based attacks.
-				This is the default behavior.
+				Equivalent to: (default behavior)
 
 	mminit_loglevel=
 			[KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -545,7 +545,8 @@ static enum spectre_v2_mitigation_cmd __
 	char arg[20];
 	int ret, i;
 
-	if (cmdline_find_option_bool(boot_command_line, "nospectre_v2"))
+	if (cmdline_find_option_bool(boot_command_line, "nospectre_v2") ||
+	    cpu_mitigations_off())
 		return SPECTRE_V2_CMD_NONE;
 
 	ret = cmdline_find_option(boot_command_line, "spectre_v2", arg, sizeof(arg));
@@ -809,7 +810,8 @@ static enum ssb_mitigation_cmd __init ss
 	char arg[20];
 	int ret, i;
 
-	if (cmdline_find_option_bool(boot_command_line, "nospec_store_bypass_disable")) {
+	if (cmdline_find_option_bool(boot_command_line, "nospec_store_bypass_disable") ||
+	    cpu_mitigations_off()) {
 		return SPEC_STORE_BYPASS_CMD_NONE;
 	} else {
 		ret = cmdline_find_option(boot_command_line, "spec_store_bypass_disable",
--- a/arch/x86/mm/kaiser.c
+++ b/arch/x86/mm/kaiser.c
@@ -10,6 +10,7 @@
 #include <linux/mm.h>
 #include <linux/uaccess.h>
 #include <linux/ftrace.h>
+#include <linux/cpu.h>
 #include <xen/xen.h>
 
 #undef pr_fmt
@@ -294,7 +295,8 @@ void __init kaiser_check_boottime_disabl
 			goto skip;
 	}
 
-	if (cmdline_find_option_bool(boot_command_line, "nopti"))
+	if (cmdline_find_option_bool(boot_command_line, "nopti") ||
+	    cpu_mitigations_off())
 		goto disable;
 
 skip:

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