arm64/speculation: Support 'mitigations=' cmdline option

Configure arm64 runtime CPU speculation bug mitigations in accordance
with the 'mitigations=' cmdline option.  This affects Meltdown, Spectre
v2, and Speculative Store Bypass.

The default behavior is unchanged.

Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
[will: reorder checks so KASLR implies KPTI and SSBS is affected by cmdline]
Signed-off-by: Will Deacon <will.deacon@arm.com>

3 files changed, 17 insertions, 5 deletions

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 6a929258faf7..ce226f7ee566 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -2545,8 +2545,8 @@
                         http://repo.or.cz/w/linux-2.6/mini2440.git
 
         mitigations=
-                        [X86,PPC,S390] Control optional mitigations for CPU
-                        vulnerabilities.  This is a set of curated,
+                        [X86,PPC,S390,ARM64] 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.
 
@@ -2555,11 +2555,13 @@
                                 improves system performance, but it may also
                                 expose users to several CPU vulnerabilities.
                                 Equivalent to: nopti [X86,PPC]
+                                               kpti=0 [ARM64]
                                                nospectre_v1 [PPC]
                                                nobp=0 [S390]
-                                               nospectre_v2 [X86,PPC,S390]
+                                               nospectre_v2 [X86,PPC,S390,ARM64]
                                                spectre_v2_user=off [X86]
                                                spec_store_bypass_disable=off [X86,PPC]
+                                               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 44ef98be001e..1b9ce0fdd81d 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>
@@ -386,6 +387,9 @@ static bool has_ssbd_mitigation(const struct arm64_cpu_capabilities *entry,
 
         WARN_ON(scope != SCOPE_LOCAL_CPU || preemptible());
 
+        if (cpu_mitigations_off())
+                ssbd_state = ARM64_SSBD_FORCE_DISABLE;
+
         /* delay setting __ssb_safe until we get a firmware response */
         if (is_midr_in_range_list(read_cpuid_id(), entry->midr_range_list))
                 this_cpu_safe = true;
@@ -589,7 +593,7 @@ check_branch_predictor(const struct arm64_cpu_capabilities *entry, int scope)
         }
 
         /* forced off */
-        if (__nospectre_v2) {
+        if (__nospectre_v2 || cpu_mitigations_off()) {
                 pr_info_once("spectrev2 mitigation disabled by command line option\n");
                 __hardenbp_enab = false;
                 return false;
diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index 703ee8564fbd..f3b32d88f165 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>
@@ -966,7 +967,7 @@ static bool unmap_kernel_at_el0(const struct arm64_cpu_capabilities *entry,
                 MIDR_ALL_VERSIONS(MIDR_HISI_TSV110),
                 { /* sentinel */ }
         };
-        char const *str = "command line option";
+        char const *str = "kpti command line option";
         bool meltdown_safe;
 
         meltdown_safe = is_midr_in_range_list(read_cpuid_id(), kpti_safe_list);
@@ -996,6 +997,11 @@ static bool unmap_kernel_at_el0(const struct arm64_cpu_capabilities *entry,
                 }
         }
 
+        if (cpu_mitigations_off() && !__kpti_forced) {
+                str = "mitigations=off";
+                __kpti_forced = -1;
+        }
+
         if (!IS_ENABLED(CONFIG_UNMAP_KERNEL_AT_EL0)) {
                 pr_info_once("kernel page table isolation disabled by kernel configuration\n");
                 return false;