arm64: Introduce separate file for spectre mitigations and reporting

The spectre mitigation code is spread over a few different files, which
makes it both hard to follow, but also hard to remove it should we want
to do that in future.

Introduce a new file for housing the spectre mitigations, and populate
it with the spectre-v1 reporting code to start with.

Signed-off-by: Will Deacon <will@kernel.org>

1 files changed, 32 insertions, 0 deletions

diff --git a/arch/arm64/kernel/proton-pack.c b/arch/arm64/kernel/proton-pack.c
new file mode 100644
index 000000000000..c37bf468e4a4
--- /dev/null
+++ b/arch/arm64/kernel/proton-pack.c
@@ -0,0 +1,32 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Handle detection, reporting and mitigation of Spectre v1, v2 and v4, as
+ * detailed at:
+ *
+ *   https://developer.arm.com/support/arm-security-updates/speculative-processor-vulnerability
+ *
+ * This code was originally written hastily under an awful lot of stress and so
+ * aspects of it are somewhat hacky. Unfortunately, changing anything in here
+ * instantly makes me feel ill. Thanks, Jann. Thann.
+ *
+ * Copyright (C) 2018 ARM Ltd, All Rights Reserved.
+ * Copyright (C) 2020 Google LLC
+ *
+ * "If there's something strange in your neighbourhood, who you gonna call?"
+ *
+ * Authors: Will Deacon <will@kernel.org> and Marc Zyngier <maz@kernel.org>
+ */
+
+#include <linux/device.h>
+
+/*
+ * Spectre v1.
+ *
+ * The kernel can't protect userspace for this one: it's each person for
+ * themselves. Advertise what we're doing and be done with it.
+ */
+ssize_t cpu_show_spectre_v1(struct device *dev, struct device_attribute *attr,
+			    char *buf)
+{
+	return sprintf(buf, "Mitigation: __user pointer sanitization\n");
+}