[PATCH RFC 5/5] arm64/speculation: Add support for 'cpu_spec_mitigations=' cmdline options

Josh Poimboeuf
2019-04-04T16:46:19Z

Configure arm64 runtime CPU speculation bug mitigations in accordance
with the 'cpu_spec_mitigations=' cmdline options. This affects
Meltdown and Speculative Store Bypass.

The default behavior is unchanged.

Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
---
Documentation/admin-guide/kernel-parameters.txt | 2 ++
arch/arm64/kernel/cpu_errata.c | 4 ++++
arch/arm64/kernel/cpufeature.c | 6 ++++++
3 files changed, 12 insertions(+)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index e838af96daa4..0b54385ee7a8 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -2553,11 +2553,13 @@
off
Disable all speculative CPU mitigations.
Equivalent to: nopti [x86, powerpc]
+ kpti=0 [arm64]
nospectre_v1 [powerpc]
nospectre_v2 [x86, powerpc, s390]
spectre_v2_user=off [x86]
nobp=0 [s390]
spec_store_bypass_disable=off [x86, powerpc]
+ ssbd=force-off [arm64]
l1tf=off [x86]

auto (default)
diff --git a/arch/arm64/kernel/cpu_errata.c b/arch/arm64/kernel/cpu_errata.c
index 9950bb0cbd52..db8d27e3fb1c 100644
--- a/arch/arm64/kernel/cpu_errata.c
+++ b/arch/arm64/kernel/cpu_errata.c
@@ -19,6 +19,7 @@
#include <linux/arm-smccc.h>
#include <linux/psci.h>
#include <linux/types.h>
+#include <linux/cpu.h>
#include <asm/cpu.h>
#include <asm/cputype.h>
#include <asm/cpufeature.h>
@@ -385,6 +386,9 @@ static bool has_ssbd_mitigation(const struct arm64_cpu_capabilities *entry,
return false;
}

+ if (cpu_spec_mitigations == CPU_SPEC_MITIGATIONS_OFF)
+ ssbd_state = ARM64_SSBD_FORCE_DISABLE;
+
switch (psci_ops.conduit) {
case PSCI_CONDUIT_HVC:
arm_smccc_1_1_hvc(ARM_SMCCC_ARCH_FEATURES_FUNC_ID,
diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index 4061de10cea6..4512b582d50f 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -25,6 +25,7 @@
#include <linux/stop_machine.h>
#include <linux/types.h>
#include <linux/mm.h>
+#include <linux/cpu.h>
#include <asm/cpu.h>
#include <asm/cpufeature.h>
#include <asm/cpu_ops.h>
@@ -978,6 +979,11 @@ static bool unmap_kernel_at_el0(const struct arm64_cpu_capabilities *entry,
__kpti_forced = -1;
}

+ if (cpu_spec_mitigations == CPU_SPEC_MITIGATIONS_OFF) {
+ str = "cpu_spec_mitigations=off";
+ __kpti_forced = -1;
+ }
+
/* Forced? */
if (__kpti_forced) {
pr_info_once("kernel page table isolation forced %s by %s\n",
--
2.17.2