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Subject[PATCH 4.19 105/114] arm64/speculation: Support mitigations= cmdline option
Date
From: Josh Poimboeuf <jpoimboe@redhat.com>

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>

---
Documentation/admin-guide/kernel-parameters.txt | 8 +++++---
arch/arm64/kernel/cpu_errata.c | 6 +++++-
arch/arm64/kernel/cpufeature.c | 8 +++++++-
3 files changed, 17 insertions(+), 5 deletions(-)

--- 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]

--- 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 st

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 arm6
}

/* 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;
--- 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 st
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 st
}
}

+ 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;

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