diff --git a/arch/x86/boot/compressed/aslr.c b/arch/x86/boot/compressed/aslr.c index 14b24e0e5496..05957986d123 100644 --- a/arch/x86/boot/compressed/aslr.c +++ b/arch/x86/boot/compressed/aslr.c @@ -3,6 +3,7 @@ #ifdef CONFIG_RANDOMIZE_BASE #include #include +#include #define I8254_PORT_CONTROL 0x43 #define I8254_PORT_COUNTER0 0x40 @@ -55,20 +56,210 @@ static unsigned long get_random_long(void) return random; } +struct mem_vector { + unsigned long start; + unsigned long size; +}; + +#define MEM_AVOID_MAX 5 +struct mem_vector mem_avoid[MEM_AVOID_MAX]; + +static bool mem_contains(struct mem_vector *region, struct mem_vector *item) +{ + /* Item at least partially before region. */ + if (item->start < region->start) + return false; + /* Item at least partially after region. */ + if (item->start + item->size > region->start + region->size) + return false; + return true; +} + +static bool mem_overlaps(struct mem_vector *one, struct mem_vector *two) +{ + /* Item one is entirely before item two. */ + if (one->start + one->size <= two->start) + return false; + /* Item one is entirely after item two. */ + if (one->start >= two->start + two->size) + return false; + return true; +} + +static void mem_avoid_init(unsigned long input, unsigned long input_size, + unsigned long output, unsigned long output_size) +{ + u64 initrd_start, initrd_size; + u64 cmd_line, cmd_line_size; + unsigned long unsafe, unsafe_len; + char *ptr; + + /* + * Avoid the region that is unsafe to overlap during + * decompression (see calculations at top of misc.c). + */ + unsafe_len = (output_size >> 12) + 32768 + 18; + unsafe = (unsigned long)input + input_size - unsafe_len; + mem_avoid[0].start = unsafe; + mem_avoid[0].size = unsafe_len; + + /* Avoid initrd. */ + initrd_start = (u64)real_mode->ext_ramdisk_image << 32; + initrd_start |= real_mode->hdr.ramdisk_image; + initrd_size = (u64)real_mode->ext_ramdisk_size << 32; + initrd_size |= real_mode->hdr.ramdisk_size; + mem_avoid[1].start = initrd_start; + mem_avoid[1].size = initrd_size; + + /* Avoid kernel command line. */ + cmd_line = (u64)real_mode->ext_cmd_line_ptr << 32; + cmd_line |= real_mode->hdr.cmd_line_ptr; + /* Calculate size of cmd_line. */ + ptr = (char *)(unsigned long)cmd_line; + for (cmd_line_size = 0; ptr[cmd_line_size++]; ) + ; + mem_avoid[2].start = cmd_line; + mem_avoid[2].size = cmd_line_size; + + /* Avoid heap memory. */ + mem_avoid[3].start = (unsigned long)free_mem_ptr; + mem_avoid[3].size = BOOT_HEAP_SIZE; + + /* Avoid stack memory. */ + mem_avoid[4].start = (unsigned long)free_mem_end_ptr; + mem_avoid[4].size = BOOT_STACK_SIZE; +} + +/* Does this memory vector overlap a known avoided area? */ +bool mem_avoid_overlap(struct mem_vector *img) +{ + int i; + + for (i = 0; i < MEM_AVOID_MAX; i++) { + if (mem_overlaps(img, &mem_avoid[i])) + return true; + } + + return false; +} + +unsigned long slots[CONFIG_RANDOMIZE_BASE_MAX_OFFSET / CONFIG_PHYSICAL_ALIGN]; +unsigned long slot_max = 0; + +static void slots_append(unsigned long addr) +{ + /* Overflowing the slots list should be impossible. */ + if (slot_max >= CONFIG_RANDOMIZE_BASE_MAX_OFFSET / + CONFIG_PHYSICAL_ALIGN) + return; + + slots[slot_max++] = addr; +} + +static unsigned long slots_fetch_random(void) +{ + /* Handle case of no slots stored. */ + if (slot_max == 0) + return 0; + + return slots[get_random_long() % slot_max]; +} + +static void process_e820_entry(struct e820entry *entry, + unsigned long minimum, + unsigned long image_size) +{ + struct mem_vector region, img; + + /* Skip non-RAM entries. */ + if (entry->type != E820_RAM) + return; + + /* Ignore entries entirely above our maximum. */ + if (entry->addr >= CONFIG_RANDOMIZE_BASE_MAX_OFFSET) + return; + + /* Ignore entries entirely below our minimum. */ + if (entry->addr + entry->size < minimum) + return; + + region.start = entry->addr; + region.size = entry->size; + + /* Potentially raise address to minimum location. */ + if (region.start < minimum) + region.start = minimum; + + /* Potentially raise address to meet alignment requirements. */ + region.start = ALIGN(region.start, CONFIG_PHYSICAL_ALIGN); + + /* Did we raise the address above the bounds of this e820 region? */ + if (region.start > entry->addr + entry->size) + return; + + /* Reduce size by any delta from the original address. */ + region.size -= region.start - entry->addr; + + /* Reduce maximum size to fit end of image within maximum limit. */ + if (region.start + region.size > CONFIG_RANDOMIZE_BASE_MAX_OFFSET) + region.size = CONFIG_RANDOMIZE_BASE_MAX_OFFSET - region.start; + + /* Walk each aligned slot and check for avoided areas. */ + for (img.start = region.start, img.size = image_size ; + mem_contains(®ion, &img) ; + img.start += CONFIG_PHYSICAL_ALIGN) { + if (mem_avoid_overlap(&img)) + continue; + slots_append(img.start); + } +} + +static unsigned long find_random_addr(unsigned long minimum, + unsigned long size) +{ + int i; + unsigned long addr; + + /* Make sure minimum is aligned. */ + minimum = ALIGN(minimum, CONFIG_PHYSICAL_ALIGN); + + /* Verify potential e820 positions, appending to slots list. */ + for (i = 0; i < real_mode->e820_entries; i++) { + process_e820_entry(&real_mode->e820_map[i], minimum, size); + } + + return slots_fetch_random(); +} + unsigned char *choose_kernel_location(unsigned char *input, unsigned long input_size, unsigned char *output, unsigned long output_size) { unsigned long choice = (unsigned long)output; + unsigned long random; if (cmdline_find_option_bool("nokaslr")) { debug_putstr("KASLR disabled...\n"); goto out; } - /* XXX: choose random location. */ + /* Record the various known unsafe memory ranges. */ + mem_avoid_init((unsigned long)input, input_size, + (unsigned long)output, output_size); + /* Walk e820 and find a random address. */ + random = find_random_addr(choice, output_size); + if (!random) { + debug_putstr("KASLR could not find suitable E820 region...\n"); + goto out; + } + + /* Always enforce the minimum. */ + if (random < choice) + goto out; + + choice = random; out: return (unsigned char *)choice; } diff --git a/arch/x86/boot/compressed/misc.c b/arch/x86/boot/compressed/misc.c index 71387685dc16..196eaf373a06 100644 --- a/arch/x86/boot/compressed/misc.c +++ b/arch/x86/boot/compressed/misc.c @@ -112,14 +112,8 @@ struct boot_params *real_mode; /* Pointer to real-mode data */ void *memset(void *s, int c, size_t n); void *memcpy(void *dest, const void *src, size_t n); -#ifdef CONFIG_X86_64 -#define memptr long -#else -#define memptr unsigned -#endif - -static memptr free_mem_ptr; -static memptr free_mem_end_ptr; +memptr free_mem_ptr; +memptr free_mem_end_ptr; static char *vidmem; static int vidport; diff --git a/arch/x86/boot/compressed/misc.h b/arch/x86/boot/compressed/misc.h index 0782eb0b6e30..24e3e569a13c 100644 --- a/arch/x86/boot/compressed/misc.h +++ b/arch/x86/boot/compressed/misc.h @@ -23,7 +23,15 @@ #define BOOT_BOOT_H #include "../ctype.h" +#ifdef CONFIG_X86_64 +#define memptr long +#else +#define memptr unsigned +#endif + /* misc.c */ +extern memptr free_mem_ptr; +extern memptr free_mem_end_ptr; extern struct boot_params *real_mode; /* Pointer to real-mode data */ void __putstr(const char *s); #define error_putstr(__x) __putstr(__x)