s390/speculation: Support 'mitigations=' cmdline option

commit 0336e04a6520bdaefdb0769d2a70084fa52e81ed upstream

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 <jpoimboe@redhat.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Jiri Kosina <jkosina@suse.cz> (on x86)
Reviewed-by: Jiri Kosina <jkosina@suse.cz>
Cc: Borislav Petkov <bp@alien8.de>
Cc: "H . Peter Anvin" <hpa@zytor.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Jiri Kosina <jikos@kernel.org>
Cc: Waiman Long <longman@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Jon Masters <jcm@redhat.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: linuxppc-dev@lists.ozlabs.org
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: linux-s390@vger.kernel.org
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-arch@vger.kernel.org
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Tyler Hicks <tyhicks@canonical.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Randy Dunlap <rdunlap@infradead.org>
Cc: Steven Price <steven.price@arm.com>
Cc: Phil Auld <pauld@redhat.com>
Link: https://lkml.kernel.org/r/e4a161805458a5ec88812aac0307ae3908a030fc.1555085500.git.jpoimboe@redhat.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 204161cee674df9080b5e52a20dc037dcabff31e..6fa7895885c92750a613ab556a4db3cb6ae2bfb0 100644 (file)
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -2389,7 +2389,7 @@
                        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.
@@ -2400,7 +2400,8 @@
                                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 d5eed651b5abd00cb556a47b58ac5551ea80566f..83e5976885623b39ff09b09966c5b8cb1c4bb05e 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/facility.h>
 #include <asm/nospec-branch.h>
 
@@ -55,8 +56,16 @@ static int __init nospectre_v2_setup_early(char *str)
 }
 early_param("nospectre_v2", nospectre_v2_setup_early);
 
+
 void __init nospec_auto_detect(void)
 {
+       if (cpu_mitigations_off()) {
+               /*
+                * Disable expolines and disable nobp.
+                */
+               if (IS_ENABLED(CC_USING_EXPOLINE))
+                       nospec_disable = 1;
+               __clear_facility(82, S390_lowcore.alt_stfle_fac_list);
        if (IS_ENABLED(CC_USING_EXPOLINE)) {
                /*
                 * The kernel has been compiled with expolines.