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Subject[PATCH 4.19 097/114] arm64: Provide a command line to disable spectre_v2 mitigation
Date
From: Jeremy Linton <jeremy.linton@arm.com>

[ Upstream commit e5ce5e7267ddcbe13ab9ead2542524e1b7993e5a ]

There are various reasons, such as benchmarking, to disable spectrev2
mitigation on a machine. Provide a command-line option to do so.

Signed-off-by: Jeremy Linton <jeremy.linton@arm.com>
Reviewed-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Reviewed-by: Andre Przywara <andre.przywara@arm.com>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Tested-by: Stefan Wahren <stefan.wahren@i2se.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: linux-doc@vger.kernel.org
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 | 13 +++++++++++++
2 files changed, 17 insertions(+), 4 deletions(-)

--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -2866,10 +2866,10 @@
(bounds check bypass). With this option data leaks
are possible in the system.

- nospectre_v2 [X86,PPC_FSL_BOOK3E] Disable all mitigations for the Spectre variant 2
- (indirect branch prediction) vulnerability. System may
- allow data leaks with this option, which is equivalent
- to spectre_v2=off.
+ nospectre_v2 [X86,PPC_FSL_BOOK3E,ARM64] Disable all mitigations for
+ the Spectre variant 2 (indirect branch prediction)
+ vulnerability. System may allow data leaks with this
+ option.

nospec_store_bypass_disable
[HW] Disable all mitigations for the Speculative Store Bypass vulnerability
--- a/arch/arm64/kernel/cpu_errata.c
+++ b/arch/arm64/kernel/cpu_errata.c
@@ -189,6 +189,14 @@ static void qcom_link_stack_sanitization
: "=&r" (tmp));
}

+static bool __nospectre_v2;
+static int __init parse_nospectre_v2(char *str)
+{
+ __nospectre_v2 = true;
+ return 0;
+}
+early_param("nospectre_v2", parse_nospectre_v2);
+
static void
enable_smccc_arch_workaround_1(const struct arm64_cpu_capabilities *entry)
{
@@ -200,6 +208,11 @@ enable_smccc_arch_workaround_1(const str
if (!entry->matches(entry, SCOPE_LOCAL_CPU))
return;

+ if (__nospectre_v2) {
+ pr_info_once("spectrev2 mitigation disabled by command line option\n");
+ return;
+ }
+
if (psci_ops.smccc_version == SMCCC_VERSION_1_0)
return;


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