1 files changed, 112 insertions, 0 deletions
diff --git a/arch/arm64/kernel/pi/kaslr_early.c b/arch/arm64/kernel/pi/kaslr_early.c
new file mode 100644
index 000000000000..6c3855e69395
--- /dev/null
+++ b/arch/arm64/kernel/pi/kaslr_early.c
@@ -0,0 +1,112 @@
+// SPDX-License-Identifier: GPL-2.0-only
+// Copyright 2022 Google LLC
+// Author: Ard Biesheuvel <ardb@google.com>
+
+// NOTE: code in this file runs *very* early, and is not permitted to use
+// global variables or anything that relies on absolute addressing.
+
+#include <linux/libfdt.h>
+#include <linux/init.h>
+#include <linux/linkage.h>
+#include <linux/types.h>
+#include <linux/sizes.h>
+#include <linux/string.h>
+
+#include <asm/archrandom.h>
+#include <asm/memory.h>
+
+/* taken from lib/string.c */
+static char *__strstr(const char *s1, const char *s2)
+{
+	size_t l1, l2;
+
+	l2 = strlen(s2);
+	if (!l2)
+		return (char *)s1;
+	l1 = strlen(s1);
+	while (l1 >= l2) {
+		l1--;
+		if (!memcmp(s1, s2, l2))
+			return (char *)s1;
+		s1++;
+	}
+	return NULL;
+}
+static bool cmdline_contains_nokaslr(const u8 *cmdline)
+{
+	const u8 *str;
+
+	str = __strstr(cmdline, "nokaslr");
+	return str == cmdline || (str > cmdline && *(str - 1) == ' ');
+}
+
+static bool is_kaslr_disabled_cmdline(void *fdt)
+{
+	if (!IS_ENABLED(CONFIG_CMDLINE_FORCE)) {
+		int node;
+		const u8 *prop;
+
+		node = fdt_path_offset(fdt, "/chosen");
+		if (node < 0)
+			goto out;
+
+		prop = fdt_getprop(fdt, node, "bootargs", NULL);
+		if (!prop)
+			goto out;
+
+		if (cmdline_contains_nokaslr(prop))
+			return true;
+
+		if (IS_ENABLED(CONFIG_CMDLINE_EXTEND))
+			goto out;
+
+		return false;
+	}
+out:
+	return cmdline_contains_nokaslr(CONFIG_CMDLINE);
+}
+
+static u64 get_kaslr_seed(void *fdt)
+{
+	int node, len;
+	fdt64_t *prop;
+	u64 ret;
+
+	node = fdt_path_offset(fdt, "/chosen");
+	if (node < 0)
+		return 0;
+
+	prop = fdt_getprop_w(fdt, node, "kaslr-seed", &len);
+	if (!prop || len != sizeof(u64))
+		return 0;
+
+	ret = fdt64_to_cpu(*prop);
+	*prop = 0;
+	return ret;
+}
+
+asmlinkage u64 kaslr_early_init(void *fdt)
+{
+	u64 seed;
+
+	if (is_kaslr_disabled_cmdline(fdt))
+		return 0;
+
+	seed = get_kaslr_seed(fdt);
+	if (!seed) {
+#ifdef CONFIG_ARCH_RANDOM
+		 if (!__early_cpu_has_rndr() ||
+		     !__arm64_rndr((unsigned long *)&seed))
+#endif
+		return 0;
+	}
+
+	/*
+	 * OK, so we are proceeding with KASLR enabled. Calculate a suitable
+	 * kernel image offset from the seed. Let's place the kernel in the
+	 * middle half of the VMALLOC area (VA_BITS_MIN - 2), and stay clear of
+	 * the lower and upper quarters to avoid colliding with other
+	 * allocations.
+	 */
+	return BIT(VA_BITS_MIN - 3) + (seed & GENMASK(VA_BITS_MIN - 3, 0));
+}