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-rw-r--r--arch/x86/boot/compressed/kaslr.c877
1 files changed, 877 insertions, 0 deletions
diff --git a/arch/x86/boot/compressed/kaslr.c b/arch/x86/boot/compressed/kaslr.c
new file mode 100644
index 000000000..b92fffbe7
--- /dev/null
+++ b/arch/x86/boot/compressed/kaslr.c
@@ -0,0 +1,877 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * kaslr.c
+ *
+ * This contains the routines needed to generate a reasonable level of
+ * entropy to choose a randomized kernel base address offset in support
+ * of Kernel Address Space Layout Randomization (KASLR). Additionally
+ * handles walking the physical memory maps (and tracking memory regions
+ * to avoid) in order to select a physical memory location that can
+ * contain the entire properly aligned running kernel image.
+ *
+ */
+
+/*
+ * isspace() in linux/ctype.h is expected by next_args() to filter
+ * out "space/lf/tab". While boot/ctype.h conflicts with linux/ctype.h,
+ * since isdigit() is implemented in both of them. Hence disable it
+ * here.
+ */
+#define BOOT_CTYPE_H
+
+#include "misc.h"
+#include "error.h"
+#include "../string.h"
+
+#include <generated/compile.h>
+#include <linux/module.h>
+#include <linux/uts.h>
+#include <linux/utsname.h>
+#include <linux/ctype.h>
+#include <linux/efi.h>
+#include <generated/utsrelease.h>
+#include <asm/efi.h>
+
+/* Macros used by the included decompressor code below. */
+#define STATIC
+#include <linux/decompress/mm.h>
+
+#define _SETUP
+#include <asm/setup.h> /* For COMMAND_LINE_SIZE */
+#undef _SETUP
+
+extern unsigned long get_cmd_line_ptr(void);
+
+/* Simplified build-specific string for starting entropy. */
+static const char build_str[] = UTS_RELEASE " (" LINUX_COMPILE_BY "@"
+ LINUX_COMPILE_HOST ") (" LINUX_COMPILER ") " UTS_VERSION;
+
+static unsigned long rotate_xor(unsigned long hash, const void *area,
+ size_t size)
+{
+ size_t i;
+ unsigned long *ptr = (unsigned long *)area;
+
+ for (i = 0; i < size / sizeof(hash); i++) {
+ /* Rotate by odd number of bits and XOR. */
+ hash = (hash << ((sizeof(hash) * 8) - 7)) | (hash >> 7);
+ hash ^= ptr[i];
+ }
+
+ return hash;
+}
+
+/* Attempt to create a simple but unpredictable starting entropy. */
+static unsigned long get_boot_seed(void)
+{
+ unsigned long hash = 0;
+
+ hash = rotate_xor(hash, build_str, sizeof(build_str));
+ hash = rotate_xor(hash, boot_params, sizeof(*boot_params));
+
+ return hash;
+}
+
+#define KASLR_COMPRESSED_BOOT
+#include "../../lib/kaslr.c"
+
+
+/* Only supporting at most 4 unusable memmap regions with kaslr */
+#define MAX_MEMMAP_REGIONS 4
+
+static bool memmap_too_large;
+
+
+/*
+ * Store memory limit: MAXMEM on 64-bit and KERNEL_IMAGE_SIZE on 32-bit.
+ * It may be reduced by "mem=nn[KMG]" or "memmap=nn[KMG]" command line options.
+ */
+static u64 mem_limit;
+
+/* Number of immovable memory regions */
+static int num_immovable_mem;
+
+enum mem_avoid_index {
+ MEM_AVOID_ZO_RANGE = 0,
+ MEM_AVOID_INITRD,
+ MEM_AVOID_CMDLINE,
+ MEM_AVOID_BOOTPARAMS,
+ MEM_AVOID_MEMMAP_BEGIN,
+ MEM_AVOID_MEMMAP_END = MEM_AVOID_MEMMAP_BEGIN + MAX_MEMMAP_REGIONS - 1,
+ MEM_AVOID_MAX,
+};
+
+static struct mem_vector mem_avoid[MEM_AVOID_MAX];
+
+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;
+}
+
+char *skip_spaces(const char *str)
+{
+ while (isspace(*str))
+ ++str;
+ return (char *)str;
+}
+#include "../../../../lib/ctype.c"
+#include "../../../../lib/cmdline.c"
+
+enum parse_mode {
+ PARSE_MEMMAP,
+ PARSE_EFI,
+};
+
+static int
+parse_memmap(char *p, u64 *start, u64 *size, enum parse_mode mode)
+{
+ char *oldp;
+
+ if (!p)
+ return -EINVAL;
+
+ /* We don't care about this option here */
+ if (!strncmp(p, "exactmap", 8))
+ return -EINVAL;
+
+ oldp = p;
+ *size = memparse(p, &p);
+ if (p == oldp)
+ return -EINVAL;
+
+ switch (*p) {
+ case '#':
+ case '$':
+ case '!':
+ *start = memparse(p + 1, &p);
+ return 0;
+ case '@':
+ if (mode == PARSE_MEMMAP) {
+ /*
+ * memmap=nn@ss specifies usable region, should
+ * be skipped
+ */
+ *size = 0;
+ } else {
+ u64 flags;
+
+ /*
+ * efi_fake_mem=nn@ss:attr the attr specifies
+ * flags that might imply a soft-reservation.
+ */
+ *start = memparse(p + 1, &p);
+ if (p && *p == ':') {
+ p++;
+ if (kstrtoull(p, 0, &flags) < 0)
+ *size = 0;
+ else if (flags & EFI_MEMORY_SP)
+ return 0;
+ }
+ *size = 0;
+ }
+ fallthrough;
+ default:
+ /*
+ * If w/o offset, only size specified, memmap=nn[KMG] has the
+ * same behaviour as mem=nn[KMG]. It limits the max address
+ * system can use. Region above the limit should be avoided.
+ */
+ *start = 0;
+ return 0;
+ }
+
+ return -EINVAL;
+}
+
+static void mem_avoid_memmap(enum parse_mode mode, char *str)
+{
+ static int i;
+
+ if (i >= MAX_MEMMAP_REGIONS)
+ return;
+
+ while (str && (i < MAX_MEMMAP_REGIONS)) {
+ int rc;
+ u64 start, size;
+ char *k = strchr(str, ',');
+
+ if (k)
+ *k++ = 0;
+
+ rc = parse_memmap(str, &start, &size, mode);
+ if (rc < 0)
+ break;
+ str = k;
+
+ if (start == 0) {
+ /* Store the specified memory limit if size > 0 */
+ if (size > 0 && size < mem_limit)
+ mem_limit = size;
+
+ continue;
+ }
+
+ mem_avoid[MEM_AVOID_MEMMAP_BEGIN + i].start = start;
+ mem_avoid[MEM_AVOID_MEMMAP_BEGIN + i].size = size;
+ i++;
+ }
+
+ /* More than 4 memmaps, fail kaslr */
+ if ((i >= MAX_MEMMAP_REGIONS) && str)
+ memmap_too_large = true;
+}
+
+/* Store the number of 1GB huge pages which users specified: */
+static unsigned long max_gb_huge_pages;
+
+static void parse_gb_huge_pages(char *param, char *val)
+{
+ static bool gbpage_sz;
+ char *p;
+
+ if (!strcmp(param, "hugepagesz")) {
+ p = val;
+ if (memparse(p, &p) != PUD_SIZE) {
+ gbpage_sz = false;
+ return;
+ }
+
+ if (gbpage_sz)
+ warn("Repeatedly set hugeTLB page size of 1G!\n");
+ gbpage_sz = true;
+ return;
+ }
+
+ if (!strcmp(param, "hugepages") && gbpage_sz) {
+ p = val;
+ max_gb_huge_pages = simple_strtoull(p, &p, 0);
+ return;
+ }
+}
+
+static void handle_mem_options(void)
+{
+ char *args = (char *)get_cmd_line_ptr();
+ size_t len;
+ char *tmp_cmdline;
+ char *param, *val;
+ u64 mem_size;
+
+ if (!args)
+ return;
+
+ len = strnlen(args, COMMAND_LINE_SIZE-1);
+ tmp_cmdline = malloc(len + 1);
+ if (!tmp_cmdline)
+ error("Failed to allocate space for tmp_cmdline");
+
+ memcpy(tmp_cmdline, args, len);
+ tmp_cmdline[len] = 0;
+ args = tmp_cmdline;
+
+ /* Chew leading spaces */
+ args = skip_spaces(args);
+
+ while (*args) {
+ args = next_arg(args, &param, &val);
+ /* Stop at -- */
+ if (!val && strcmp(param, "--") == 0)
+ break;
+
+ if (!strcmp(param, "memmap")) {
+ mem_avoid_memmap(PARSE_MEMMAP, val);
+ } else if (IS_ENABLED(CONFIG_X86_64) && strstr(param, "hugepages")) {
+ parse_gb_huge_pages(param, val);
+ } else if (!strcmp(param, "mem")) {
+ char *p = val;
+
+ if (!strcmp(p, "nopentium"))
+ continue;
+ mem_size = memparse(p, &p);
+ if (mem_size == 0)
+ break;
+
+ if (mem_size < mem_limit)
+ mem_limit = mem_size;
+ } else if (!strcmp(param, "efi_fake_mem")) {
+ mem_avoid_memmap(PARSE_EFI, val);
+ }
+ }
+
+ free(tmp_cmdline);
+ return;
+}
+
+/*
+ * In theory, KASLR can put the kernel anywhere in the range of [16M, MAXMEM)
+ * on 64-bit, and [16M, KERNEL_IMAGE_SIZE) on 32-bit.
+ *
+ * The mem_avoid array is used to store the ranges that need to be avoided
+ * when KASLR searches for an appropriate random address. We must avoid any
+ * regions that are unsafe to overlap with during decompression, and other
+ * things like the initrd, cmdline and boot_params. This comment seeks to
+ * explain mem_avoid as clearly as possible since incorrect mem_avoid
+ * memory ranges lead to really hard to debug boot failures.
+ *
+ * The initrd, cmdline, and boot_params are trivial to identify for
+ * avoiding. They are MEM_AVOID_INITRD, MEM_AVOID_CMDLINE, and
+ * MEM_AVOID_BOOTPARAMS respectively below.
+ *
+ * What is not obvious how to avoid is the range of memory that is used
+ * during decompression (MEM_AVOID_ZO_RANGE below). This range must cover
+ * the compressed kernel (ZO) and its run space, which is used to extract
+ * the uncompressed kernel (VO) and relocs.
+ *
+ * ZO's full run size sits against the end of the decompression buffer, so
+ * we can calculate where text, data, bss, etc of ZO are positioned more
+ * easily.
+ *
+ * For additional background, the decompression calculations can be found
+ * in header.S, and the memory diagram is based on the one found in misc.c.
+ *
+ * The following conditions are already enforced by the image layouts and
+ * associated code:
+ * - input + input_size >= output + output_size
+ * - kernel_total_size <= init_size
+ * - kernel_total_size <= output_size (see Note below)
+ * - output + init_size >= output + output_size
+ *
+ * (Note that kernel_total_size and output_size have no fundamental
+ * relationship, but output_size is passed to choose_random_location
+ * as a maximum of the two. The diagram is showing a case where
+ * kernel_total_size is larger than output_size, but this case is
+ * handled by bumping output_size.)
+ *
+ * The above conditions can be illustrated by a diagram:
+ *
+ * 0 output input input+input_size output+init_size
+ * | | | | |
+ * | | | | |
+ * |-----|--------|--------|--------------|-----------|--|-------------|
+ * | | |
+ * | | |
+ * output+init_size-ZO_INIT_SIZE output+output_size output+kernel_total_size
+ *
+ * [output, output+init_size) is the entire memory range used for
+ * extracting the compressed image.
+ *
+ * [output, output+kernel_total_size) is the range needed for the
+ * uncompressed kernel (VO) and its run size (bss, brk, etc).
+ *
+ * [output, output+output_size) is VO plus relocs (i.e. the entire
+ * uncompressed payload contained by ZO). This is the area of the buffer
+ * written to during decompression.
+ *
+ * [output+init_size-ZO_INIT_SIZE, output+init_size) is the worst-case
+ * range of the copied ZO and decompression code. (i.e. the range
+ * covered backwards of size ZO_INIT_SIZE, starting from output+init_size.)
+ *
+ * [input, input+input_size) is the original copied compressed image (ZO)
+ * (i.e. it does not include its run size). This range must be avoided
+ * because it contains the data used for decompression.
+ *
+ * [input+input_size, output+init_size) is [_text, _end) for ZO. This
+ * range includes ZO's heap and stack, and must be avoided since it
+ * performs the decompression.
+ *
+ * Since the above two ranges need to be avoided and they are adjacent,
+ * they can be merged, resulting in: [input, output+init_size) which
+ * becomes the MEM_AVOID_ZO_RANGE below.
+ */
+static void mem_avoid_init(unsigned long input, unsigned long input_size,
+ unsigned long output)
+{
+ unsigned long init_size = boot_params->hdr.init_size;
+ u64 initrd_start, initrd_size;
+ unsigned long cmd_line, cmd_line_size;
+
+ /*
+ * Avoid the region that is unsafe to overlap during
+ * decompression.
+ */
+ mem_avoid[MEM_AVOID_ZO_RANGE].start = input;
+ mem_avoid[MEM_AVOID_ZO_RANGE].size = (output + init_size) - input;
+
+ /* Avoid initrd. */
+ initrd_start = (u64)boot_params->ext_ramdisk_image << 32;
+ initrd_start |= boot_params->hdr.ramdisk_image;
+ initrd_size = (u64)boot_params->ext_ramdisk_size << 32;
+ initrd_size |= boot_params->hdr.ramdisk_size;
+ mem_avoid[MEM_AVOID_INITRD].start = initrd_start;
+ mem_avoid[MEM_AVOID_INITRD].size = initrd_size;
+ /* No need to set mapping for initrd, it will be handled in VO. */
+
+ /* Avoid kernel command line. */
+ cmd_line = get_cmd_line_ptr();
+ /* Calculate size of cmd_line. */
+ if (cmd_line) {
+ cmd_line_size = strnlen((char *)cmd_line, COMMAND_LINE_SIZE-1) + 1;
+ mem_avoid[MEM_AVOID_CMDLINE].start = cmd_line;
+ mem_avoid[MEM_AVOID_CMDLINE].size = cmd_line_size;
+ }
+
+ /* Avoid boot parameters. */
+ mem_avoid[MEM_AVOID_BOOTPARAMS].start = (unsigned long)boot_params;
+ mem_avoid[MEM_AVOID_BOOTPARAMS].size = sizeof(*boot_params);
+
+ /* We don't need to set a mapping for setup_data. */
+
+ /* Mark the memmap regions we need to avoid */
+ handle_mem_options();
+
+ /* Enumerate the immovable memory regions */
+ num_immovable_mem = count_immovable_mem_regions();
+}
+
+/*
+ * Does this memory vector overlap a known avoided area? If so, record the
+ * overlap region with the lowest address.
+ */
+static bool mem_avoid_overlap(struct mem_vector *img,
+ struct mem_vector *overlap)
+{
+ int i;
+ struct setup_data *ptr;
+ u64 earliest = img->start + img->size;
+ bool is_overlapping = false;
+
+ for (i = 0; i < MEM_AVOID_MAX; i++) {
+ if (mem_overlaps(img, &mem_avoid[i]) &&
+ mem_avoid[i].start < earliest) {
+ *overlap = mem_avoid[i];
+ earliest = overlap->start;
+ is_overlapping = true;
+ }
+ }
+
+ /* Avoid all entries in the setup_data linked list. */
+ ptr = (struct setup_data *)(unsigned long)boot_params->hdr.setup_data;
+ while (ptr) {
+ struct mem_vector avoid;
+
+ avoid.start = (unsigned long)ptr;
+ avoid.size = sizeof(*ptr) + ptr->len;
+
+ if (mem_overlaps(img, &avoid) && (avoid.start < earliest)) {
+ *overlap = avoid;
+ earliest = overlap->start;
+ is_overlapping = true;
+ }
+
+ if (ptr->type == SETUP_INDIRECT &&
+ ((struct setup_indirect *)ptr->data)->type != SETUP_INDIRECT) {
+ avoid.start = ((struct setup_indirect *)ptr->data)->addr;
+ avoid.size = ((struct setup_indirect *)ptr->data)->len;
+
+ if (mem_overlaps(img, &avoid) && (avoid.start < earliest)) {
+ *overlap = avoid;
+ earliest = overlap->start;
+ is_overlapping = true;
+ }
+ }
+
+ ptr = (struct setup_data *)(unsigned long)ptr->next;
+ }
+
+ return is_overlapping;
+}
+
+struct slot_area {
+ u64 addr;
+ unsigned long num;
+};
+
+#define MAX_SLOT_AREA 100
+
+static struct slot_area slot_areas[MAX_SLOT_AREA];
+static unsigned int slot_area_index;
+static unsigned long slot_max;
+
+static void store_slot_info(struct mem_vector *region, unsigned long image_size)
+{
+ struct slot_area slot_area;
+
+ if (slot_area_index == MAX_SLOT_AREA)
+ return;
+
+ slot_area.addr = region->start;
+ slot_area.num = 1 + (region->size - image_size) / CONFIG_PHYSICAL_ALIGN;
+
+ slot_areas[slot_area_index++] = slot_area;
+ slot_max += slot_area.num;
+}
+
+/*
+ * Skip as many 1GB huge pages as possible in the passed region
+ * according to the number which users specified:
+ */
+static void
+process_gb_huge_pages(struct mem_vector *region, unsigned long image_size)
+{
+ u64 pud_start, pud_end;
+ unsigned long gb_huge_pages;
+ struct mem_vector tmp;
+
+ if (!IS_ENABLED(CONFIG_X86_64) || !max_gb_huge_pages) {
+ store_slot_info(region, image_size);
+ return;
+ }
+
+ /* Are there any 1GB pages in the region? */
+ pud_start = ALIGN(region->start, PUD_SIZE);
+ pud_end = ALIGN_DOWN(region->start + region->size, PUD_SIZE);
+
+ /* No good 1GB huge pages found: */
+ if (pud_start >= pud_end) {
+ store_slot_info(region, image_size);
+ return;
+ }
+
+ /* Check if the head part of the region is usable. */
+ if (pud_start >= region->start + image_size) {
+ tmp.start = region->start;
+ tmp.size = pud_start - region->start;
+ store_slot_info(&tmp, image_size);
+ }
+
+ /* Skip the good 1GB pages. */
+ gb_huge_pages = (pud_end - pud_start) >> PUD_SHIFT;
+ if (gb_huge_pages > max_gb_huge_pages) {
+ pud_end = pud_start + (max_gb_huge_pages << PUD_SHIFT);
+ max_gb_huge_pages = 0;
+ } else {
+ max_gb_huge_pages -= gb_huge_pages;
+ }
+
+ /* Check if the tail part of the region is usable. */
+ if (region->start + region->size >= pud_end + image_size) {
+ tmp.start = pud_end;
+ tmp.size = region->start + region->size - pud_end;
+ store_slot_info(&tmp, image_size);
+ }
+}
+
+static u64 slots_fetch_random(void)
+{
+ unsigned long slot;
+ unsigned int i;
+
+ /* Handle case of no slots stored. */
+ if (slot_max == 0)
+ return 0;
+
+ slot = kaslr_get_random_long("Physical") % slot_max;
+
+ for (i = 0; i < slot_area_index; i++) {
+ if (slot >= slot_areas[i].num) {
+ slot -= slot_areas[i].num;
+ continue;
+ }
+ return slot_areas[i].addr + ((u64)slot * CONFIG_PHYSICAL_ALIGN);
+ }
+
+ if (i == slot_area_index)
+ debug_putstr("slots_fetch_random() failed!?\n");
+ return 0;
+}
+
+static void __process_mem_region(struct mem_vector *entry,
+ unsigned long minimum,
+ unsigned long image_size)
+{
+ struct mem_vector region, overlap;
+ u64 region_end;
+
+ /* Enforce minimum and memory limit. */
+ region.start = max_t(u64, entry->start, minimum);
+ region_end = min(entry->start + entry->size, mem_limit);
+
+ /* Give up if slot area array is full. */
+ while (slot_area_index < MAX_SLOT_AREA) {
+ /* Potentially raise address to meet alignment needs. */
+ region.start = ALIGN(region.start, CONFIG_PHYSICAL_ALIGN);
+
+ /* Did we raise the address above the passed in memory entry? */
+ if (region.start > region_end)
+ return;
+
+ /* Reduce size by any delta from the original address. */
+ region.size = region_end - region.start;
+
+ /* Return if region can't contain decompressed kernel */
+ if (region.size < image_size)
+ return;
+
+ /* If nothing overlaps, store the region and return. */
+ if (!mem_avoid_overlap(&region, &overlap)) {
+ process_gb_huge_pages(&region, image_size);
+ return;
+ }
+
+ /* Store beginning of region if holds at least image_size. */
+ if (overlap.start >= region.start + image_size) {
+ region.size = overlap.start - region.start;
+ process_gb_huge_pages(&region, image_size);
+ }
+
+ /* Clip off the overlapping region and start over. */
+ region.start = overlap.start + overlap.size;
+ }
+}
+
+static bool process_mem_region(struct mem_vector *region,
+ unsigned long minimum,
+ unsigned long image_size)
+{
+ int i;
+ /*
+ * If no immovable memory found, or MEMORY_HOTREMOVE disabled,
+ * use @region directly.
+ */
+ if (!num_immovable_mem) {
+ __process_mem_region(region, minimum, image_size);
+
+ if (slot_area_index == MAX_SLOT_AREA) {
+ debug_putstr("Aborted e820/efi memmap scan (slot_areas full)!\n");
+ return 1;
+ }
+ return 0;
+ }
+
+#if defined(CONFIG_MEMORY_HOTREMOVE) && defined(CONFIG_ACPI)
+ /*
+ * If immovable memory found, filter the intersection between
+ * immovable memory and @region.
+ */
+ for (i = 0; i < num_immovable_mem; i++) {
+ u64 start, end, entry_end, region_end;
+ struct mem_vector entry;
+
+ if (!mem_overlaps(region, &immovable_mem[i]))
+ continue;
+
+ start = immovable_mem[i].start;
+ end = start + immovable_mem[i].size;
+ region_end = region->start + region->size;
+
+ entry.start = clamp(region->start, start, end);
+ entry_end = clamp(region_end, start, end);
+ entry.size = entry_end - entry.start;
+
+ __process_mem_region(&entry, minimum, image_size);
+
+ if (slot_area_index == MAX_SLOT_AREA) {
+ debug_putstr("Aborted e820/efi memmap scan when walking immovable regions(slot_areas full)!\n");
+ return 1;
+ }
+ }
+#endif
+ return 0;
+}
+
+#ifdef CONFIG_EFI
+/*
+ * Returns true if we processed the EFI memmap, which we prefer over the E820
+ * table if it is available.
+ */
+static bool
+process_efi_entries(unsigned long minimum, unsigned long image_size)
+{
+ struct efi_info *e = &boot_params->efi_info;
+ bool efi_mirror_found = false;
+ struct mem_vector region;
+ efi_memory_desc_t *md;
+ unsigned long pmap;
+ char *signature;
+ u32 nr_desc;
+ int i;
+
+ signature = (char *)&e->efi_loader_signature;
+ if (strncmp(signature, EFI32_LOADER_SIGNATURE, 4) &&
+ strncmp(signature, EFI64_LOADER_SIGNATURE, 4))
+ return false;
+
+#ifdef CONFIG_X86_32
+ /* Can't handle data above 4GB at this time */
+ if (e->efi_memmap_hi) {
+ warn("EFI memmap is above 4GB, can't be handled now on x86_32. EFI should be disabled.\n");
+ return false;
+ }
+ pmap = e->efi_memmap;
+#else
+ pmap = (e->efi_memmap | ((__u64)e->efi_memmap_hi << 32));
+#endif
+
+ nr_desc = e->efi_memmap_size / e->efi_memdesc_size;
+ for (i = 0; i < nr_desc; i++) {
+ md = efi_early_memdesc_ptr(pmap, e->efi_memdesc_size, i);
+ if (md->attribute & EFI_MEMORY_MORE_RELIABLE) {
+ efi_mirror_found = true;
+ break;
+ }
+ }
+
+ for (i = 0; i < nr_desc; i++) {
+ md = efi_early_memdesc_ptr(pmap, e->efi_memdesc_size, i);
+
+ /*
+ * Here we are more conservative in picking free memory than
+ * the EFI spec allows:
+ *
+ * According to the spec, EFI_BOOT_SERVICES_{CODE|DATA} are also
+ * free memory and thus available to place the kernel image into,
+ * but in practice there's firmware where using that memory leads
+ * to crashes.
+ *
+ * Only EFI_CONVENTIONAL_MEMORY is guaranteed to be free.
+ */
+ if (md->type != EFI_CONVENTIONAL_MEMORY)
+ continue;
+
+ if (efi_soft_reserve_enabled() &&
+ (md->attribute & EFI_MEMORY_SP))
+ continue;
+
+ if (efi_mirror_found &&
+ !(md->attribute & EFI_MEMORY_MORE_RELIABLE))
+ continue;
+
+ region.start = md->phys_addr;
+ region.size = md->num_pages << EFI_PAGE_SHIFT;
+ if (process_mem_region(&region, minimum, image_size))
+ break;
+ }
+ return true;
+}
+#else
+static inline bool
+process_efi_entries(unsigned long minimum, unsigned long image_size)
+{
+ return false;
+}
+#endif
+
+static void process_e820_entries(unsigned long minimum,
+ unsigned long image_size)
+{
+ int i;
+ struct mem_vector region;
+ struct boot_e820_entry *entry;
+
+ /* Verify potential e820 positions, appending to slots list. */
+ for (i = 0; i < boot_params->e820_entries; i++) {
+ entry = &boot_params->e820_table[i];
+ /* Skip non-RAM entries. */
+ if (entry->type != E820_TYPE_RAM)
+ continue;
+ region.start = entry->addr;
+ region.size = entry->size;
+ if (process_mem_region(&region, minimum, image_size))
+ break;
+ }
+}
+
+static unsigned long find_random_phys_addr(unsigned long minimum,
+ unsigned long image_size)
+{
+ u64 phys_addr;
+
+ /* Bail out early if it's impossible to succeed. */
+ if (minimum + image_size > mem_limit)
+ return 0;
+
+ /* Check if we had too many memmaps. */
+ if (memmap_too_large) {
+ debug_putstr("Aborted memory entries scan (more than 4 memmap= args)!\n");
+ return 0;
+ }
+
+ if (!process_efi_entries(minimum, image_size))
+ process_e820_entries(minimum, image_size);
+
+ phys_addr = slots_fetch_random();
+
+ /* Perform a final check to make sure the address is in range. */
+ if (phys_addr < minimum || phys_addr + image_size > mem_limit) {
+ warn("Invalid physical address chosen!\n");
+ return 0;
+ }
+
+ return (unsigned long)phys_addr;
+}
+
+static unsigned long find_random_virt_addr(unsigned long minimum,
+ unsigned long image_size)
+{
+ unsigned long slots, random_addr;
+
+ /*
+ * There are how many CONFIG_PHYSICAL_ALIGN-sized slots
+ * that can hold image_size within the range of minimum to
+ * KERNEL_IMAGE_SIZE?
+ */
+ slots = 1 + (KERNEL_IMAGE_SIZE - minimum - image_size) / CONFIG_PHYSICAL_ALIGN;
+
+ random_addr = kaslr_get_random_long("Virtual") % slots;
+
+ return random_addr * CONFIG_PHYSICAL_ALIGN + minimum;
+}
+
+/*
+ * Since this function examines addresses much more numerically,
+ * it takes the input and output pointers as 'unsigned long'.
+ */
+void choose_random_location(unsigned long input,
+ unsigned long input_size,
+ unsigned long *output,
+ unsigned long output_size,
+ unsigned long *virt_addr)
+{
+ unsigned long random_addr, min_addr;
+
+ if (cmdline_find_option_bool("nokaslr")) {
+ warn("KASLR disabled: 'nokaslr' on cmdline.");
+ return;
+ }
+
+ boot_params->hdr.loadflags |= KASLR_FLAG;
+
+ if (IS_ENABLED(CONFIG_X86_32))
+ mem_limit = KERNEL_IMAGE_SIZE;
+ else
+ mem_limit = MAXMEM;
+
+ /* Record the various known unsafe memory ranges. */
+ mem_avoid_init(input, input_size, *output);
+
+ /*
+ * Low end of the randomization range should be the
+ * smaller of 512M or the initial kernel image
+ * location:
+ */
+ min_addr = min(*output, 512UL << 20);
+ /* Make sure minimum is aligned. */
+ min_addr = ALIGN(min_addr, CONFIG_PHYSICAL_ALIGN);
+
+ /* Walk available memory entries to find a random address. */
+ random_addr = find_random_phys_addr(min_addr, output_size);
+ if (!random_addr) {
+ warn("Physical KASLR disabled: no suitable memory region!");
+ } else {
+ /* Update the new physical address location. */
+ if (*output != random_addr)
+ *output = random_addr;
+ }
+
+
+ /* Pick random virtual address starting from LOAD_PHYSICAL_ADDR. */
+ if (IS_ENABLED(CONFIG_X86_64))
+ random_addr = find_random_virt_addr(LOAD_PHYSICAL_ADDR, output_size);
+ *virt_addr = random_addr;
+}
generated by cgit v1.2.3 (git 2.39.1) at 2024-11-27 01:20:02 +0000