summaryrefslogtreecommitdiff
path: root/arch/arm64/kernel/kaslr.c
diff options
context:
space:
mode:
Diffstat (limited to 'arch/arm64/kernel/kaslr.c')
-rw-r--r--arch/arm64/kernel/kaslr.c177
1 files changed, 177 insertions, 0 deletions
diff --git a/arch/arm64/kernel/kaslr.c b/arch/arm64/kernel/kaslr.c
new file mode 100644
index 000000000000..582983920054
--- /dev/null
+++ b/arch/arm64/kernel/kaslr.c
@@ -0,0 +1,177 @@
+/*
+ * Copyright (C) 2016 Linaro Ltd <ard.biesheuvel@linaro.org>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+
+#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 <asm/fixmap.h>
+#include <asm/kernel-pgtable.h>
+#include <asm/memory.h>
+#include <asm/mmu.h>
+#include <asm/pgtable.h>
+#include <asm/sections.h>
+
+u64 __read_mostly module_alloc_base;
+u16 __initdata memstart_offset_seed;
+
+static __init u64 get_kaslr_seed(void *fdt)
+{
+ int node, len;
+ u64 *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 *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;
+}
+
+extern void *__init __fixmap_remap_fdt(phys_addr_t dt_phys, int *size,
+ pgprot_t prot);
+
+/*
+ * 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;
+ 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;
+
+ /*
+ * 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)
+ return 0;
+
+ /*
+ * Retrieve (and wipe) the seed from the FDT
+ */
+ seed = get_kaslr_seed(fdt);
+ if (!seed)
+ return 0;
+
+ /*
+ * Check if 'nokaslr' appears on the command line, and
+ * return 0 if that is the case.
+ */
+ cmdline = get_cmdline(fdt);
+ str = strstr(cmdline, "nokaslr");
+ if (str == cmdline || (str > cmdline && *(str - 1) == ' '))
+ 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
+ * lower half of the VMALLOC area (VA_BITS - 2).
+ * 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 - 2)) - 1) & ~(SZ_2M - 1);
+ offset = seed & mask;
+
+ /* use the top 16 bits to randomize the linear region */
+ memstart_offset_seed = seed >> 48;
+
+ /*
+ * The kernel Image should not extend across a 1GB/32MB/512MB alignment
+ * boundary (for 4KB/16KB/64KB granule kernels, respectively). If this
+ * happens, increase the KASLR offset by the size of the kernel image.
+ */
+ if ((((u64)_text + offset) >> SWAPPER_TABLE_SHIFT) !=
+ (((u64)_end + offset) >> SWAPPER_TABLE_SHIFT))
+ offset = (offset + (u64)(_end - _text)) & mask;
+
+ 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.
+ */
+ return offset;
+
+ if (IS_ENABLED(CONFIG_RANDOMIZE_MODULE_REGION_FULL)) {
+ /*
+ * Randomize the module region independently from the core
+ * kernel. This prevents modules from leaking any 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 = VMALLOC_END - VMALLOC_START - MODULES_VSIZE;
+ module_alloc_base = VMALLOC_START;
+ } 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;
+
+ return offset;
+}