Subject: [PATCH 4.4 248/266] x86/speculation: Support mitigations= cmdline option

From: Greg Kroah-Hartman <[email-masked]>
Date: Wed, 15 May 2019 12:55:55 +0200

From: Josh Poimboeuf <[email-masked]>

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 <[email-masked]>
Signed-off-by: Thomas Gleixner <[email-masked]>
Tested-by: Jiri Kosina <[email-masked]> (on x86)
Reviewed-by: Jiri Kosina <[email-masked]>
Cc: Borislav Petkov <[email-masked]>
Cc: "H . Peter Anvin" <[email-masked]>
Cc: Andy Lutomirski <[email-masked]>
Cc: Peter Zijlstra <[email-masked]>
Cc: Jiri Kosina <[email-masked]>
Cc: Waiman Long <[email-masked]>
Cc: Andrea Arcangeli <[email-masked]>
Cc: Jon Masters <[email-masked]>
Cc: Benjamin Herrenschmidt <[email-masked]>
Cc: Paul Mackerras <[email-masked]>
Cc: Michael Ellerman <[email-masked]>
Cc: [email-masked]
Cc: Martin Schwidefsky <[email-masked]>
Cc: Heiko Carstens <[email-masked]>
Cc: [email-masked]
Cc: Catalin Marinas <[email-masked]>
Cc: Will Deacon <[email-masked]>
Cc: [email-masked]
Cc: [email-masked]
Cc: Greg Kroah-Hartman <[email-masked]>
Cc: Tyler Hicks <[email-masked]>
Cc: Linus Torvalds <[email-masked]>
Cc: Randy Dunlap <[email-masked]>
Cc: Steven Price <[email-masked]>
Cc: Phil Auld <[email-masked]>
Link: https://lkml.kernel.org/r/[email-masked]
[bwh: Backported to 4.4:
 - Drop the auto,nosmt option and the l1tf mitigation selection, which we can't
   support
 - Adjust filenames, context]
Signed-off-by: Ben Hutchings <[email-masked]>
Signed-off-by: Greg Kroah-Hartman <[email-masked]>
---
 Documentation/kernel-parameters.txt |   14 +++++++++-----
 arch/x86/kernel/cpu/bugs.c          |    6 ++++--
 arch/x86/mm/kaiser.c                |    4 +++-
 3 files changed, 16 insertions(+), 8 deletions(-)

--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -2174,15 +2174,19 @@ 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
@@ -2190,7 +2194,7 @@ 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
@@ -479,7 +479,8 @@ 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));
@@ -743,7 +744,8 @@ 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>
 
 #undef pr_fmt
 #define pr_fmt(fmt)     "Kernel/User page tables isolation: " fmt
@@ -297,7 +298,8 @@ 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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