linux-kernel - [PATCH 4.19 097/114] arm64: Provide a command line to disable spectre

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Date:   Thu, 10 Oct 2019 10:36:44 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Jeremy Linton <jeremy.linton@....com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Andre Przywara <andre.przywara@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Stefan Wahren <stefan.wahren@...e.com>,
        Jonathan Corbet <corbet@....net>, linux-doc@...r.kernel.org,
        Will Deacon <will.deacon@....com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>
Subject: [PATCH 4.19 097/114] arm64: Provide a command line to disable spectre_v2 mitigation

From: Jeremy Linton <jeremy.linton@....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@....com>
Reviewed-by: Suzuki K Poulose <suzuki.poulose@....com>
Reviewed-by: Andre Przywara <andre.przywara@....com>
Reviewed-by: Catalin Marinas <catalin.marinas@....com>
Tested-by: Stefan Wahren <stefan.wahren@...e.com>
Cc: Jonathan Corbet <corbet@....net>
Cc: linux-doc@...r.kernel.org
Signed-off-by: Will Deacon <will.deacon@....com>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@...aro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.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;