s390/speculation: Support 'mitigations=' cmdline option

Configure s390 runtime CPU speculation bug mitigations in accordance
with the 'mitigations=' cmdline option.  This affects Spectre v1 and
Spectre v2.

The default behavior is unchanged.

Signed-off-by: Josh Poimboeuf <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>
Tested-by: Jiri Kosina <[email protected]> (on x86)
Reviewed-by: Jiri Kosina <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: "H . Peter Anvin" <[email protected]>
Cc: Andy Lutomirski <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Jiri Kosina <[email protected]>
Cc: Waiman Long <[email protected]>
Cc: Andrea Arcangeli <[email protected]>
Cc: Jon Masters <[email protected]>
Cc: Benjamin Herrenschmidt <[email protected]>
Cc: Paul Mackerras <[email protected]>
Cc: Michael Ellerman <[email protected]>
Cc: [email protected]
Cc: Martin Schwidefsky <[email protected]>
Cc: Heiko Carstens <[email protected]>
Cc: [email protected]
Cc: Catalin Marinas <[email protected]>
Cc: Will Deacon <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: Greg Kroah-Hartman <[email protected]>
Cc: Tyler Hicks <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Randy Dunlap <[email protected]>
Cc: Steven Price <[email protected]>
Cc: Phil Auld <[email protected]>
Link: https://lkml.kernel.org/r/e4a161805458a5ec88812aac0307ae3908a030fc.1555085500.git.jpoimboe@redhat.com

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index ac7150a25a7a15fa0fcc7f0a1a88000ccd37bcd1..1ae93872b79fd8f165dc7564d5a73c6b2d412811 100644 (file)
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -2514,7 +2514,7 @@
                        http://repo.or.cz/w/linux-2.6/mini2440.git
 
        mitigations=
-                       [X86,PPC] Control optional mitigations for CPU
+                       [X86,PPC,S390] 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.
@@ -2525,7 +2525,8 @@
                                expose users to several CPU vulnerabilities.
                                Equivalent to: nopti [X86,PPC]
                                               nospectre_v1 [PPC]
-                                              nospectre_v2 [X86,PPC]
+                                              nobp=0 [S390]
+                                              nospectre_v2 [X86,PPC,S390]
                                               spectre_v2_user=off [X86]
                                               spec_store_bypass_disable=off [X86,PPC]
                                               l1tf=off [X86]

diff --git a/arch/s390/kernel/nospec-branch.c b/arch/s390/kernel/nospec-branch.c
index bdddaae9655984dfbf59ccee386c7bb3608cb183..649135cbedd5c4407f16d89f4020d5022f40395e 100644 (file)
--- a/arch/s390/kernel/nospec-branch.c
+++ b/arch/s390/kernel/nospec-branch.c
@@ -1,6 +1,7 @@
 // SPDX-License-Identifier: GPL-2.0
 #include <linux/module.h>
 #include <linux/device.h>
+#include <linux/cpu.h>
 #include <asm/nospec-branch.h>
 
 static int __init nobp_setup_early(char *str)
@@ -58,7 +59,7 @@ early_param("nospectre_v2", nospectre_v2_setup_early);
 
 void __init nospec_auto_detect(void)
 {
-       if (test_facility(156)) {
+       if (test_facility(156) || cpu_mitigations_off()) {
                /*
                 * The machine supports etokens.
                 * Disable expolines and disable nobp.