1 files changed, 218 insertions, 0 deletions
diff --git a/arch/arm64/kernel/kaslr.c b/arch/arm64/kernel/kaslr.c
new file mode 100644
index 000000000..b181e0544
--- /dev/null
+++ b/arch/arm64/kernel/kaslr.c
@@ -0,0 +1,218 @@
+// 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/cacheflush.h>
+#include <asm/fixmap.h>
+#include <asm/kernel-pgtable.h>
+#include <asm/memory.h>
+#include <asm/mmu.h>
+#include <asm/sections.h>
+
+enum kaslr_status {
+	KASLR_ENABLED,
+	KASLR_DISABLED_CMDLINE,
+	KASLR_DISABLED_NO_SEED,
+	KASLR_DISABLED_FDT_REMAP,
+};
+
+static enum kaslr_status __initdata kaslr_status;
+u64 __ro_after_init module_alloc_base;
+u16 __initdata memstart_offset_seed;
+
+static __init 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;
+}
+
+static __init const u8 *kaslr_get_cmdline(void *fdt)
+{
+	static __initconst const u8 default_cmdline[] = CONFIG_CMDLINE;
+
+	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;
+		return prop;
+	}
+out:
+	return default_cmdline;
+}
+
+/*
+ * This routine will be executed with the kernel mapped at its default virtual
+ * address, and if it returns successfully, the kernel will be remapped, and
+ * start_kernel() will be executed from a randomized virtual offset. The
+ * relocation will result in all absolute references (e.g., static variables
+ * containing function pointers) to be reinitialized, and zero-initialized
+ * .bss variables will be reset to 0.
+ */
+u64 __init kaslr_early_init(u64 dt_phys)
+{
+	void *fdt;
+	u64 seed, offset, mask, module_range;
+	const u8 *cmdline, *str;
+	unsigned long raw;
+	int size;
+
+	/*
+	 * 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;
+	__flush_dcache_area(&module_alloc_base, sizeof(module_alloc_base));
+
+	/*
+	 * Try to map the FDT early. If this fails, we simply bail,
+	 * and proceed with KASLR disabled. We will make another
+	 * attempt at mapping the FDT in setup_machine()
+	 */
+	early_fixmap_init();
+	fdt = fixmap_remap_fdt(dt_phys, &size, PAGE_KERNEL);
+	if (!fdt) {
+		kaslr_status = KASLR_DISABLED_FDT_REMAP;
+		return 0;
+	}
+
+	/*
+	 * Retrieve (and wipe) the seed from the FDT
+	 */
+	seed = get_kaslr_seed(fdt);
+
+	/*
+	 * Check if 'nokaslr' appears on the command line, and
+	 * return 0 if that is the case.
+	 */
+	cmdline = kaslr_get_cmdline(fdt);
+	str = strstr(cmdline, "nokaslr");
+	if (str == cmdline || (str > cmdline && *(str - 1) == ' ')) {
+		kaslr_status = KASLR_DISABLED_CMDLINE;
+		return 0;
+	}
+
+	/*
+	 * Mix in any entropy obtainable architecturally if enabled
+	 * and supported.
+	 */
+
+	if (arch_get_random_seed_long_early(&raw))
+		seed ^= raw;
+
+	if (!seed) {
+		kaslr_status = KASLR_DISABLED_NO_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.
+	 * Even if we could randomize at page granularity for 16k and 64k pages,
+	 * let's always round to 2 MB so we don't interfere with the ability to
+	 * map using contiguous PTEs
+	 */
+	mask = ((1UL << (VA_BITS_MIN - 2)) - 1) & ~(SZ_2M - 1);
+	offset = BIT(VA_BITS_MIN - 3) + (seed & mask);
+
+	/* use the top 16 bits to randomize the linear region */
+	memstart_offset_seed = seed >> 48;
+
+	if (IS_ENABLED(CONFIG_KASAN))
+		/*
+		 * KASAN 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 is shadowed
+		 * by KASAN zero pages. So keep modules out of the vmalloc
+		 * region if KASAN is enabled, and put the kernel well within
+		 * 4 GB of the module region.
+		 */
+		return offset % SZ_2G;
+
+	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 + offset - 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.
+		 */
+		module_range = MODULES_VSIZE - (u64)(_etext - _stext);
+		module_alloc_base = (u64)_etext + offset - MODULES_VSIZE;
+	}
+
+	/* 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;
+
+	__flush_dcache_area(&module_alloc_base, sizeof(module_alloc_base));
+	__flush_dcache_area(&memstart_offset_seed, sizeof(memstart_offset_seed));
+
+	return offset;
+}
+
+static int __init kaslr_init(void)
+{
+	switch (kaslr_status) {
+	case KASLR_ENABLED:
+		pr_info("KASLR enabled\n");
+		break;
+	case KASLR_DISABLED_CMDLINE:
+		pr_info("KASLR disabled on command line\n");
+		break;
+	case KASLR_DISABLED_NO_SEED:
+		pr_warn("KASLR disabled due to lack of seed\n");
+		break;
+	case KASLR_DISABLED_FDT_REMAP:
+		pr_warn("KASLR disabled due to FDT remapping failure\n");
+		break;
+	}
+
+	return 0;
+}
+core_initcall(kaslr_init)