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-rw-r--r--arch/arm64/kernel/pi/kaslr_early.c110
1 files changed, 110 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 000000000..17bff6e39
--- /dev/null
+++ b/arch/arm64/kernel/pi/kaslr_early.c
@@ -0,0 +1,110 @@
+// 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) {
+ if (!__early_cpu_has_rndr() ||
+ !__arm64_rndr((unsigned long *)&seed))
+ 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));
+}