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Subject[tip:core/speculation] x86/speculation: Support 'mitigations=' cmdline option
Commit-ID:  d68be4c4d31295ff6ae34a8ddfaa4c1a8ff42812
Gitweb: https://git.kernel.org/tip/d68be4c4d31295ff6ae34a8ddfaa4c1a8ff42812
Author: Josh Poimboeuf <jpoimboe@redhat.com>
AuthorDate: Fri, 12 Apr 2019 15:39:29 -0500
Committer: Thomas Gleixner <tglx@linutronix.de>
CommitDate: Wed, 17 Apr 2019 21:37:28 +0200

x86/speculation: Support 'mitigations=' cmdline option

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

---
Documentation/admin-guide/kernel-parameters.txt | 16 +++++++++++-----
arch/x86/kernel/cpu/bugs.c | 11 +++++++++--
arch/x86/mm/pti.c | 4 +++-
3 files changed, 23 insertions(+), 8 deletions(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 720ffa9c4e04..779ddeb2929c 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -2514,15 +2514,20 @@
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]
+ l1tf=off [X86]

auto (default)
Mitigate all CPU vulnerabilities, but leave SMT
@@ -2530,12 +2535,13 @@
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)

auto,nosmt
Mitigate all CPU vulnerabilities, disabling SMT
if needed. This is for users who always want to
be fully mitigated, even if it means losing SMT.
+ Equivalent to: l1tf=flush,nosmt [X86]

mminit_loglevel=
[KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index 01874d54f4fd..435c078c2948 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -440,7 +440,8 @@ static enum spectre_v2_mitigation_cmd __init spectre_v2_parse_cmdline(void)
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));
@@ -672,7 +673,8 @@ static enum ssb_mitigation_cmd __init ssb_parse_cmdline(void)
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",
@@ -996,6 +998,11 @@ static void __init l1tf_select_mitigation(void)
if (!boot_cpu_has_bug(X86_BUG_L1TF))
return;

+ if (cpu_mitigations_off())
+ l1tf_mitigation = L1TF_MITIGATION_OFF;
+ else if (cpu_mitigations_auto_nosmt())
+ l1tf_mitigation = L1TF_MITIGATION_FLUSH_NOSMT;
+
override_cache_bits(&boot_cpu_data);

switch (l1tf_mitigation) {
diff --git a/arch/x86/mm/pti.c b/arch/x86/mm/pti.c
index 4fee5c3003ed..5890f09bfc19 100644
--- a/arch/x86/mm/pti.c
+++ b/arch/x86/mm/pti.c
@@ -35,6 +35,7 @@
#include <linux/spinlock.h>
#include <linux/mm.h>
#include <linux/uaccess.h>
+#include <linux/cpu.h>

#include <asm/cpufeature.h>
#include <asm/hypervisor.h>
@@ -115,7 +116,8 @@ void __init pti_check_boottime_disable(void)
}
}

- if (cmdline_find_option_bool(boot_command_line, "nopti")) {
+ if (cmdline_find_option_bool(boot_command_line, "nopti") ||
+ cpu_mitigations_off()) {
pti_mode = PTI_FORCE_OFF;
pti_print_if_insecure("disabled on command line.");
return;
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