arm64/speculation: Support 'mitigations=' cmdline option

commit a111b7c0f20e13b54df2fa959b3dc0bdf1925ae6 upstream.

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>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
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 cc2f5c9..16607b1 100644 (file)
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -2503,8 +2503,8 @@
                        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.
 
@@ -2513,12 +2513,14 @@
                                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_v1 [X86]
-                                              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]
                                               mds=off [X86]
 

diff --git a/arch/arm64/kernel/cpu_errata.c b/arch/arm64/kernel/cpu_errata.c
index bb28eab..9ccf169 100644 (file)
--- 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>
@@ -355,6 +356,9 @@ 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;
@@ -600,7 +604,7 @@ 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 e636d37..ff5beb5 100644 (file)
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -24,6 +24,7 @@
 #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>
@@ -907,7 +908,7 @@ static bool unmap_kernel_at_el0(const struct arm64_cpu_capabilities *entry,
                MIDR_ALL_VERSIONS(MIDR_CORTEX_A73),
                { /* 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);
@@ -937,6 +938,11 @@ 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;