[PATCH 3.16 80/86] x86/speculation: Support 'mitigations=' cmdline option

Ben Hutchings
2019-05-16T15:59:35Z

From: Josh Poimboeuf <jpoimboe@redhat.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@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/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@decadent.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;