1 files changed, 93 insertions, 0 deletions
diff --git a/arch/arm64/kernel/kaslr.c b/arch/arm64/kernel/kaslr.c
new file mode 100644
index 000000000..325455d16
--- /dev/null
+++ b/arch/arm64/kernel/kaslr.c
@@ -0,0 +1,93 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2016 Linaro Ltd <ard.biesheuvel@linaro.org>
+ */
+
+#include <linux/cache.h>
+#include <linux/crc32.h>
+#include <linux/init.h>
+#include <linux/libfdt.h>
+#include <linux/mm_types.h>
+#include <linux/sched.h>
+#include <linux/types.h>
+#include <linux/pgtable.h>
+#include <linux/random.h>
+
+#include <asm/fixmap.h>
+#include <asm/kernel-pgtable.h>
+#include <asm/memory.h>
+#include <asm/mmu.h>
+#include <asm/sections.h>
+#include <asm/setup.h>
+
+u64 __ro_after_init module_alloc_base;
+u16 __initdata memstart_offset_seed;
+
+struct arm64_ftr_override kaslr_feature_override __initdata;
+
+static int __init kaslr_init(void)
+{
+	u64 module_range;
+	u32 seed;
+
+	/*
+	 * Set a reasonable default for module_alloc_base in case
+	 * we end up running with module randomization disabled.
+	 */
+	module_alloc_base = (u64)_etext - MODULES_VSIZE;
+
+	if (kaslr_feature_override.val & kaslr_feature_override.mask & 0xf) {
+		pr_info("KASLR disabled on command line\n");
+		return 0;
+	}
+
+	if (!kaslr_offset()) {
+		pr_warn("KASLR disabled due to lack of seed\n");
+		return 0;
+	}
+
+	pr_info("KASLR enabled\n");
+
+	/*
+	 * KASAN without KASAN_VMALLOC does not expect the module region to
+	 * intersect the vmalloc region, since shadow memory is allocated for
+	 * each module at load time, whereas the vmalloc region will already be
+	 * shadowed by KASAN zero pages.
+	 */
+	BUILD_BUG_ON((IS_ENABLED(CONFIG_KASAN_GENERIC) ||
+	              IS_ENABLED(CONFIG_KASAN_SW_TAGS)) &&
+		     !IS_ENABLED(CONFIG_KASAN_VMALLOC));
+
+	seed = get_random_u32();
+
+	if (IS_ENABLED(CONFIG_RANDOMIZE_MODULE_REGION_FULL)) {
+		/*
+		 * Randomize the module region over a 2 GB window covering the
+		 * kernel. This reduces the risk of modules leaking information
+		 * about the address of the kernel itself, but results in
+		 * branches between modules and the core kernel that are
+		 * resolved via PLTs. (Branches between modules will be
+		 * resolved normally.)
+		 */
+		module_range = SZ_2G - (u64)(_end - _stext);
+		module_alloc_base = max((u64)_end - SZ_2G, (u64)MODULES_VADDR);
+	} else {
+		/*
+		 * Randomize the module region by setting module_alloc_base to
+		 * a PAGE_SIZE multiple in the range [_etext - MODULES_VSIZE,
+		 * _stext) . This guarantees that the resulting region still
+		 * covers [_stext, _etext], and that all relative branches can
+		 * be resolved without veneers unless this region is exhausted
+		 * and we fall back to a larger 2GB window in module_alloc()
+		 * when ARM64_MODULE_PLTS is enabled.
+		 */
+		module_range = MODULES_VSIZE - (u64)(_etext - _stext);
+	}
+
+	/* use the lower 21 bits to randomize the base of the module region */
+	module_alloc_base += (module_range * (seed & ((1 << 21) - 1))) >> 21;
+	module_alloc_base &= PAGE_MASK;
+
+	return 0;
+}
+subsys_initcall(kaslr_init)