new file mode 100644
@@ -0,0 +1,151 @@
+=====================================================================
+Function Granular Kernel Address Space Layout Randomization (fgkaslr)
+=====================================================================
+
+:Date: 6 April 2020
+:Author: Kristen Accardi
+
+Kernel Address Space Layout Randomization (KASLR) was merged into the kernel
+with the objective of increasing the difficulty of code reuse attacks. Code
+reuse attacks reused existing code snippets to get around existing memory
+protections. They exploit software bugs which expose addresses of useful code
+snippets to control the flow of execution for their own nefarious purposes.
+KASLR as it was originally implemented moves the entire kernel code text as a
+unit at boot time in order to make addresses less predictable. The order of the
+code within the segment is unchanged - only the base address is shifted. There
+are a few shortcomings to this algorithm.
+
+1. Low Entropy - there are only so many locations the kernel can fit in. This
+ means an attacker could guess without too much trouble.
+2. Knowledge of a single address can reveal the offset of the base address,
+ exposing all other locations for a published/known kernel image.
+3. Info leaks abound.
+
+Finer grained ASLR has been proposed as a way to make ASLR more resistant
+to info leaks. It is not a new concept at all, and there are many variations
+possible. Function reordering is an implementation of finer grained ASLR
+which randomizes the layout of an address space on a function level
+granularity. We use the term "fgkaslr" in this document to refer to the
+technique of function reordering when used with KASLR, as well as finer grained
+KASLR in general.
+
+Implementation Details
+======================
+
+The over-arching objective of the fgkaslr implementation is incremental
+improvement over what we already have, as well as something that can be
+merged and deployed with as little disruption to our existing kernel/ecosystem
+as possible. It is designed to work with the existing solution, and there are
+two main area where code changes occur: Build time, and Load time.
+
+Build time
+----------
+
+GCC has an option to place functions into individual .text sections. We can
+use this option to implement function reordering at load time. The final
+compiled vmlinux retains all the section headers, which can be used to help
+us find the address ranges of each function. Using this information and
+an expanded table of relocation addresses, we can shuffle the individual
+text sections immediately after decompression. You are probably asking
+yourself how this could possibly work given the number of tables of
+addresses that exist inside the kernel today for features such as exception
+handling and kprobes. Most of these tables generate relocations and
+require a simple update, and some tables that have assumptions about order
+require sorting after the update. In order to modify these tables, we
+preserve a few key symbols from the objcopy symbol stripping process for use
+after shuffling the text segments.
+
+Load time
+---------
+
+The boot kernel was modified to parse the vmlinux elf file after
+decompression to check for our interesting symbols that we kept, and to
+look for any .text.* sections to randomize. We then shuffle the sections
+and update any tables that need to be updated or resorted. The existing
+code which updated relocation addresses was modified to account for not
+just a fixed delta from the load address, but the offset that the function
+section was moved to. This requires inspection of each address to see if
+it was impacted by a randomization. In order to hide our new layout,
+symbols reported through /proc/kallsyms will be sorted by name alphabetically
+rather than by address.
+
+Security Considerations
+=======================
+
+The objective of this patch set is to improve a technology that is already
+merged into the kernel (KASLR). Obviously, this code is not a one stop
+shopping place for blocking code reuse attacks, but should instead be
+considered as one of several tools that can be used. In particular, this
+code is meant to make KASLR more effective in the presence of info leaks.
+A key point to note is that we are basically accepting that there are
+many and various ways to leak address today and in the future, and rather
+than assume that we can stop them all, we should find a method which makes
+individual info leaks less important. How much entropy we are adding to
+the existing entropy of standard KASLR will depend on a few variables.
+Firstly and most obviously, the number of functions you randomize matters.
+This implementation keeps the existing .text section for code that cannot be
+randomized - for example, because it was assembly code, or we opted out of
+randomization for performance reasons. The less sections to randomize, the
+less entropy. In addition, due to alignment (16 bytes for x86_64), the number
+of bits in a address that the attacker needs to guess is reduced, as the lower
+bits are identical.
+
+Performance Impact
+==================
+
+There are two areas where function reordering can impact performance: boot
+time latency, and run time performance.
+
+Boot time latency
+-----------------
+
+This implementation of finer grained KASLR impacts the boot time of the kernel
+in several places. It requires additional parsing of the kernel ELF file to
+obtain the section headers of the sections to be randomized. It calls the
+random number generator for each section to be randomized to determine that
+section's new memory location. It copies the decompressed kernel into a new
+area of memory to avoid corruption when laying out the newly randomized
+sections. It increases the number of relocations the kernel has to perform at
+boot time vs. standard KASLR, and it also requires a lookup on each address
+that needs to be relocated to see if it was in a randomized section and needs
+to be adjusted by a new offset. Finally, it re-sorts a few data tables that
+are required to be sorted by address.
+
+Booting a test VM on a modern, well appointed system showed an increase in
+latency of approximately 1 second.
+
+Run time
+--------
+
+The performance impact at run-time of function reordering varies by workload.
+Randomly reordering the functions will cause an increase in cache misses
+for some workloads. You should expect to see some workloads perform
+significantly worse under FGKASLR, while others stay the same or even
+mysteriously improve. In general, it will depend on the code flow whether or
+not finer grained KASLR will impact your workload, and how the underlying code
+was designed.
+
+Image Size
+==========
+
+fgkaslr increases the size of the kernel binary due to the extra section
+headers that are included, as well as the extra relocations that need to
+be added. You can expect fgkaslr to increase the size of the resulting
+vmlinux by about 3%, and the compressed image (bzImage) by 15%.
+
+Building
+========
+
+To enable fine grained KASLR, you need to have the following config options
+set (including all the ones you would use to build normal KASLR)
+
+``CONFIG_FG_KASLR=y``
+
+In addition, fgkaslr is only supported for the X86_64 architecture.
+
+Modules
+=======
+
+Modules are randomized similarly to the rest of the kernel by shuffling
+the sections at load time prior to moving them into memory. The module must
+also have been build with the -ffunction-sections compiler option.
@@ -7,6 +7,7 @@ Security Documentation
credentials
IMA-templates
+ fgkaslr
keys/index
lsm
lsm-development
@@ -80,10 +80,12 @@ vmlinux-objs-y := $(obj)/vmlinux.lds $(obj)/kernel_info.o $(obj)/head_$(BITS).o
vmlinux-objs-$(CONFIG_EARLY_PRINTK) += $(obj)/early_serial_console.o
vmlinux-objs-$(CONFIG_RANDOMIZE_BASE) += $(obj)/kaslr.o
+vmlinux-objs-$(CONFIG_FG_KASLR) += $(obj)/utils.o
ifdef CONFIG_X86_64
vmlinux-objs-$(CONFIG_RANDOMIZE_BASE) += $(obj)/kaslr_64.o
vmlinux-objs-y += $(obj)/mem_encrypt.o
vmlinux-objs-y += $(obj)/pgtable_64.o
+ vmlinux-objs-$(CONFIG_FG_KASLR) += $(obj)/fgkaslr.o
endif
vmlinux-objs-$(CONFIG_ACPI) += $(obj)/acpi.o
@@ -120,6 +122,7 @@ OBJCOPYFLAGS_vmlinux.bin := -R .comment -S
ifdef CONFIG_FG_KASLR
RELOCS_ARGS += --fg-kaslr
+ OBJCOPYFLAGS += --keep-symbols=$(srctree)/$(src)/vmlinux.symbols
endif
$(obj)/vmlinux.bin: vmlinux FORCE
new file mode 100644
@@ -0,0 +1,809 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * fgkaslr.c
+ *
+ * This contains the routines needed to reorder the kernel text section
+ * at boot time.
+ */
+#include "misc.h"
+#include "error.h"
+#include "pgtable.h"
+#include "../string.h"
+#include "../voffset.h"
+#include <linux/sort.h>
+#include <linux/bsearch.h>
+#include "../../include/asm/extable.h"
+#include "../../include/asm/orc_types.h"
+
+/*
+ * Longest parameter of 'fgkaslr=' is 'off' right now, plus an extra '\0'
+ * for termination.
+ */
+#define MAX_FGKASLR_ARG_LENGTH 4
+int nofgkaslr;
+
+/*
+ * Use normal definitions of mem*() from string.c. There are already
+ * included header files which expect a definition of memset() and by
+ * the time we define memset macro, it is too late.
+ */
+#undef memcpy
+#undef memset
+#define memzero(s, n) memset((s), 0, (n))
+#define memmove memmove
+
+void *memmove(void *dest, const void *src, size_t n);
+
+static unsigned long percpu_start;
+static unsigned long percpu_end;
+
+static long kallsyms_names;
+static long kallsyms_offsets;
+static long kallsyms_num_syms;
+static long kallsyms_relative_base;
+static long kallsyms_markers;
+static long __start___ex_table_addr;
+static long __stop___ex_table_addr;
+static long _stext;
+static long _etext;
+static long _sinittext;
+static long _einittext;
+static long __start_orc_unwind_ip;
+static long __stop_orc_unwind_ip;
+static long __start_orc_unwind;
+static long __stop_orc_unwind;
+
+/* addresses in mapped address space */
+static int *base;
+static u8 *names;
+static unsigned long relative_base;
+static unsigned int *markers_addr;
+
+struct kallsyms_name {
+ u8 len;
+ u8 indecis[256];
+};
+struct kallsyms_name *names_table;
+
+struct orc_entry *cur_orc_table;
+int *cur_orc_ip_table;
+
+/*
+ * This is an array of pointers to sections headers for randomized sections
+ */
+Elf64_Shdr **sections;
+
+/*
+ * This is an array of all section headers, randomized or otherwise.
+ */
+Elf64_Shdr *sechdrs;
+
+/*
+ * The number of elements in the randomized section header array (sections)
+ */
+int sections_size;
+
+static bool is_text(long addr)
+{
+ if ((addr >= _stext && addr < _etext) ||
+ (addr >= _sinittext && addr < _einittext))
+ return true;
+ return false;
+}
+
+bool is_percpu_addr(long pc, long offset)
+{
+ unsigned long ptr;
+ long address;
+
+ address = pc + offset + 4;
+
+ ptr = (unsigned long) address;
+
+ if (ptr >= percpu_start && ptr < percpu_end)
+ return true;
+
+ return false;
+}
+
+static int cmp_section_addr(const void *a, const void *b)
+{
+ unsigned long ptr = (unsigned long)a;
+ Elf64_Shdr *s = *(Elf64_Shdr **)b;
+ unsigned long end = s->sh_addr + s->sh_size;
+
+ if (ptr >= s->sh_addr && ptr < end)
+ return 0;
+
+ if (ptr < s->sh_addr)
+ return -1;
+
+ return 1;
+}
+
+/*
+ * Discover if the address is in a randomized section and if so, adjust
+ * by the saved offset.
+ */
+Elf64_Shdr *adjust_address(long *address)
+{
+ Elf64_Shdr **s;
+ Elf64_Shdr *shdr;
+
+ if (nofgkaslr)
+ return NULL;
+
+ s = bsearch((const void *)*address, sections, sections_size, sizeof(*s),
+ cmp_section_addr);
+ if (s != NULL) {
+ shdr = *s;
+ *address += shdr->sh_offset;
+ return shdr;
+ }
+
+ return NULL;
+}
+
+void adjust_relative_offset(long pc, long *value, Elf64_Shdr *section)
+{
+ Elf64_Shdr *s;
+ long address;
+
+ if (nofgkaslr)
+ return;
+
+ /*
+ * sometimes we are updating a relative offset that would
+ * normally be relative to the next instruction (such as a call).
+ * In this case to calculate the target, you need to add 32bits to
+ * the pc to get the next instruction value. However, sometimes
+ * targets are just data that was stored in a table such as ksymtab
+ * or cpu alternatives. In this case our target is not relative to
+ * the next instruction.
+ */
+
+ /*
+ * Calculate the address that this offset would call.
+ */
+ if (!is_text(pc))
+ address = pc + *value;
+ else
+ address = pc + *value + 4;
+
+ /*
+ * if the address is in section that was randomized,
+ * we need to adjust the offset.
+ */
+ s = adjust_address(&address);
+ if (s != NULL)
+ *value += s->sh_offset;
+
+ /*
+ * If the PC that this offset was calculated for was in a section
+ * that has been randomized, the value needs to be adjusted by the
+ * same amount as the randomized section was adjusted from it's original
+ * location.
+ */
+ if (section != NULL)
+ *value -= section->sh_offset;
+
+}
+
+static void kallsyms_swp(void *a, void *b, int size)
+{
+ int idx1, idx2;
+ int temp;
+ struct kallsyms_name name_a;
+
+ /* determine our index into the array */
+ idx1 = (int *)a - base;
+ idx2 = (int *)b - base;
+ temp = base[idx1];
+ base[idx1] = base[idx2];
+ base[idx2] = temp;
+
+ /* also swap the names table */
+ memcpy(&name_a, &names_table[idx1], sizeof(name_a));
+ memcpy(&names_table[idx1], &names_table[idx2],
+ sizeof(struct kallsyms_name));
+ memcpy(&names_table[idx2], &name_a, sizeof(struct kallsyms_name));
+}
+
+static int kallsyms_cmp(const void *a, const void *b)
+{
+ int addr_a, addr_b;
+ unsigned long uaddr_a, uaddr_b;
+
+ addr_a = *(int *)a;
+ addr_b = *(int *)b;
+
+ if (addr_a >= 0)
+ uaddr_a = addr_a;
+ if (addr_b >= 0)
+ uaddr_b = addr_b;
+
+ if (addr_a < 0)
+ uaddr_a = relative_base - 1 - addr_a;
+ if (addr_b < 0)
+ uaddr_b = relative_base - 1 - addr_b;
+
+ if (uaddr_b > uaddr_a)
+ return -1;
+
+ return 0;
+}
+
+static void deal_with_names(int num_syms)
+{
+ int num_bytes;
+ int i, j;
+ int offset;
+
+
+ /* we should have num_syms kallsyms_name entries */
+ num_bytes = num_syms * sizeof(*names_table);
+ names_table = malloc(num_syms * sizeof(*names_table));
+ if (names_table == NULL) {
+ debug_putstr("\nbytes requested: ");
+ debug_puthex(num_bytes);
+ error("\nunable to allocate space for names table\n");
+ }
+
+ /* read all the names entries */
+ offset = 0;
+ for (i = 0; i < num_syms; i++) {
+ names_table[i].len = names[offset];
+ offset++;
+ for (j = 0; j < names_table[i].len; j++) {
+ names_table[i].indecis[j] = names[offset];
+ offset++;
+ }
+ }
+}
+
+static void write_sorted_names(int num_syms)
+{
+ int i, j;
+ int offset = 0;
+ unsigned int *markers;
+
+ /*
+ * we are going to need to regenerate the markers table, which is a
+ * table of offsets into the compressed stream every 256 symbols.
+ * this code copied almost directly from scripts/kallsyms.c
+ */
+ markers = malloc(sizeof(unsigned int) * ((num_syms + 255) / 256));
+ if (!markers) {
+ debug_putstr("\nfailed to allocate heap space of ");
+ debug_puthex(((num_syms + 255) / 256));
+ debug_putstr(" bytes\n");
+ error("Unable to allocate space for markers table");
+ }
+
+ for (i = 0; i < num_syms; i++) {
+ if ((i & 0xFF) == 0)
+ markers[i >> 8] = offset;
+
+ names[offset] = (u8) names_table[i].len;
+ offset++;
+ for (j = 0; j < names_table[i].len; j++) {
+ names[offset] = (u8) names_table[i].indecis[j];
+ offset++;
+ }
+ }
+
+ /* write new markers table over old one */
+ for (i = 0; i < ((num_syms + 255) >> 8); i++)
+ markers_addr[i] = markers[i];
+
+ free(markers);
+ free(names_table);
+}
+
+static void sort_kallsyms(unsigned long map)
+{
+ int num_syms;
+ int i;
+
+ debug_putstr("\nRe-sorting kallsyms ...");
+
+ num_syms = *(int *)(kallsyms_num_syms + map);
+ base = (int *)(kallsyms_offsets + map);
+ relative_base = *(unsigned long *)(kallsyms_relative_base + map);
+ markers_addr = (unsigned int *)(kallsyms_markers + map);
+ names = (u8 *)(kallsyms_names + map);
+
+ /*
+ * the kallsyms table was generated prior to any randomization.
+ * it is a bunch of offsets from "relative base". In order for
+ * us to check if a symbol has an address that was in a randomized
+ * section, we need to reconstruct the address to it's original
+ * value prior to handle_relocations.
+ */
+ for (i = 0; i < num_syms; i++) {
+ unsigned long addr;
+ int new_base;
+
+ /*
+ * according to kernel/kallsyms.c, positive offsets are absolute
+ * values and negative offsets are relative to the base.
+ */
+ if (base[i] >= 0)
+ addr = base[i];
+ else
+ addr = relative_base - 1 - base[i];
+
+ if (adjust_address(&addr)) {
+ /* here we need to recalcuate the offset */
+ new_base = relative_base - 1 - addr;
+ base[i] = new_base;
+ }
+ }
+
+ /*
+ * here we need to read in all the kallsyms_names info
+ * so that we can regenerate it.
+ */
+ deal_with_names(num_syms);
+
+ sort(base, num_syms, sizeof(int), kallsyms_cmp, kallsyms_swp);
+
+ /* write the newly sorted names table over the old one */
+ write_sorted_names(num_syms);
+}
+
+#define ARCH_HAS_SEARCH_EXTABLE
+#include "../../../../lib/extable.c"
+
+static inline unsigned long
+ex_fixup_handler(const struct exception_table_entry *x)
+{
+ return ((unsigned long)&x->handler + x->handler);
+}
+
+static inline unsigned long
+ex_fixup_addr(const struct exception_table_entry *x)
+{
+ return ((unsigned long)&x->fixup + x->fixup);
+}
+
+static void update_ex_table(unsigned long map)
+{
+ struct exception_table_entry *start_ex_table = (struct exception_table_entry *) (__start___ex_table_addr + map);
+ struct exception_table_entry *stop_ex_table = (struct exception_table_entry *) (__stop___ex_table_addr + map);
+ int num_entries = (__stop___ex_table_addr - __start___ex_table_addr) / sizeof(struct exception_table_entry);
+ int i;
+
+ debug_putstr("\nUpdating exception table...\n");
+ for (i = 0; i < num_entries; i++) {
+ unsigned long insn = ex_to_insn(&start_ex_table[i]);
+ unsigned long fixup = ex_fixup_addr(&start_ex_table[i]);
+ unsigned long handler = ex_fixup_handler(&start_ex_table[i]);
+ unsigned long addr;
+ Elf64_Shdr *s;
+
+ /* check each address to see if it needs adjusting */
+ addr = insn - map;
+ s = adjust_address(&addr);
+ if (s != NULL)
+ start_ex_table[i].insn += s->sh_offset;
+
+ addr = fixup - map;
+ s = adjust_address(&addr);
+ if (s != NULL)
+ start_ex_table[i].fixup += s->sh_offset;
+
+ addr = handler - map;
+ s = adjust_address(&addr);
+ if (s != NULL)
+ start_ex_table[i].handler += s->sh_offset;
+ }
+}
+
+static void sort_ex_table(unsigned long map)
+{
+ struct exception_table_entry *start_ex_table = (struct exception_table_entry *) (__start___ex_table_addr + map);
+ struct exception_table_entry *stop_ex_table = (struct exception_table_entry *) (__stop___ex_table_addr + map);
+
+ debug_putstr("\nRe-sorting exception table...\n");
+
+ sort_extable(start_ex_table, stop_ex_table);
+}
+
+static inline unsigned long orc_ip(const int *ip)
+{
+ return (unsigned long)ip + *ip;
+}
+
+static void orc_sort_swap(void *_a, void *_b, int size)
+{
+ struct orc_entry *orc_a, *orc_b;
+ struct orc_entry orc_tmp;
+ int *a = _a, *b = _b, tmp;
+ int delta = _b - _a;
+
+ /* Swap the .orc_unwind_ip entries: */
+ tmp = *a;
+ *a = *b + delta;
+ *b = tmp - delta;
+
+ /* Swap the corresponding .orc_unwind entries: */
+ orc_a = cur_orc_table + (a - cur_orc_ip_table);
+ orc_b = cur_orc_table + (b - cur_orc_ip_table);
+ orc_tmp = *orc_a;
+ *orc_a = *orc_b;
+ *orc_b = orc_tmp;
+}
+
+static int orc_sort_cmp(const void *_a, const void *_b)
+{
+ struct orc_entry *orc_a;
+ const int *a = _a, *b = _b;
+ unsigned long a_val = orc_ip(a);
+ unsigned long b_val = orc_ip(b);
+
+ if (a_val > b_val)
+ return 1;
+ if (a_val < b_val)
+ return -1;
+
+ /*
+ * The "weak" section terminator entries need to always be on the left
+ * to ensure the lookup code skips them in favor of real entries.
+ * These terminator entries exist to handle any gaps created by
+ * whitelisted .o files which didn't get objtool generation.
+ */
+ orc_a = cur_orc_table + (a - cur_orc_ip_table);
+ return orc_a->sp_reg == ORC_REG_UNDEFINED && !orc_a->end ? -1 : 1;
+}
+
+static void sort_orc_table(unsigned long map)
+{
+ int num_entries = (__stop_orc_unwind_ip - __start_orc_unwind_ip) / sizeof(int);
+
+ cur_orc_ip_table = (int *)(__start_orc_unwind_ip + map);
+ cur_orc_table = (struct orc_entry *)(__start_orc_unwind + map);
+
+ debug_putstr("\nRe-sorting orc tables...\n");
+ sort(cur_orc_ip_table, num_entries, sizeof(int),
+ orc_sort_cmp, orc_sort_swap);
+}
+
+void post_relocations_cleanup(unsigned long map)
+{
+ if (!nofgkaslr) {
+ update_ex_table(map);
+ sort_ex_table(map);
+ sort_orc_table(map);
+ }
+
+ /*
+ * maybe one day free will do something. So, we "free" this memory
+ * in either case
+ */
+ free(sections);
+ free(sechdrs);
+}
+
+void pre_relocations_cleanup(unsigned long map)
+{
+ if (nofgkaslr)
+ return;
+
+ sort_kallsyms(map);
+}
+
+static void shuffle_sections(int *list, int size)
+{
+ int i;
+ unsigned long j;
+ int temp;
+
+ for (i = size - 1; i > 0; i--) {
+ j = kaslr_get_random_long(NULL) % (i + 1);
+
+ temp = list[i];
+ list[i] = list[j];
+ list[j] = temp;
+ }
+}
+
+static void move_text(int num_sections, char *secstrings, Elf64_Shdr *text,
+ void *source, void *dest, Elf64_Phdr *phdr)
+{
+ unsigned long adjusted_addr;
+ int copy_bytes;
+ void *stash;
+ Elf64_Shdr **sorted_sections;
+ int *index_list;
+
+ memmove(dest, source + text->sh_offset, text->sh_size);
+ copy_bytes = text->sh_size;
+ dest += text->sh_size;
+ adjusted_addr = text->sh_addr + text->sh_size;
+
+ /*
+ * we leave the sections sorted in their original order
+ * by s->sh_addr, but shuffle the indexes in a random
+ * order for copying.
+ */
+ index_list = malloc(sizeof(int) * num_sections);
+ if (!index_list)
+ error("Failed to allocate space for index list");
+
+ for (int i = 0; i < num_sections; i++)
+ index_list[i] = i;
+
+ shuffle_sections(index_list, num_sections);
+
+ /*
+ * to avoid overwriting earlier sections before they can get
+ * copied to dest, stash everything into a buffer first.
+ * this will cause our source address to be off by
+ * phdr->p_offset though, so we'll adjust s->sh_offset below.
+ *
+ * TBD: ideally we'd simply decompress higher up so that our
+ * copy wasn't in danger of overwriting anything important.
+ */
+ stash = malloc(phdr->p_filesz);
+ if (!stash)
+ error("Failed to allocate space for text stash");
+
+ memcpy(stash, source + phdr->p_offset, phdr->p_filesz);
+
+ /* now we'd walk through the sections. */
+ for (int j = 0; j < num_sections; j++) {
+ unsigned long aligned_addr;
+ Elf64_Shdr *s;
+ const char *sname;
+ void *src;
+ int pad_bytes;
+
+ s = sections[index_list[j]];
+
+ sname = secstrings + s->sh_name;
+
+ /* align addr for this section */
+ aligned_addr = ALIGN(adjusted_addr, s->sh_addralign);
+
+ /*
+ * copy out of stash, so adjust offset
+ */
+ src = stash + s->sh_offset - phdr->p_offset;
+
+ /*
+ * Fill any space between sections with int3
+ */
+ pad_bytes = aligned_addr - adjusted_addr;
+ for (int i = 0; i < pad_bytes; i++)
+ ((u8 *)dest)[i] = 0xcc;
+
+ dest = (void *) ALIGN((unsigned long)dest, s->sh_addralign);
+
+ memmove(dest, src, s->sh_size);
+
+ dest += s->sh_size;
+ copy_bytes += s->sh_size + pad_bytes;
+ adjusted_addr = aligned_addr + s->sh_size;
+
+ /* we can blow away sh_offset for our own uses */
+ s->sh_offset = aligned_addr - s->sh_addr;
+ }
+
+ free(index_list);
+
+ /*
+ * move remainder of text segment. Ok to just use original source
+ * here since this area is untouched.
+ */
+ memmove(dest, source + text->sh_offset + copy_bytes,
+ phdr->p_filesz - copy_bytes);
+ free(stash);
+}
+
+#define GET_SYM(name) \
+ do { \
+ if (strcmp(#name, strtab + sym->st_name) == 0) {\
+ name = sym->st_value; \
+ continue; \
+ } \
+ } while (0)
+
+static void parse_symtab(Elf64_Sym *symtab, char *strtab, long num_syms)
+{
+ Elf64_Sym *sym;
+
+ if (symtab == NULL || strtab == NULL)
+ return;
+
+ debug_putstr("\nLooking for symbols... ");
+
+ /*
+ * walk through the symbol table looking for the symbols
+ * that we care about.
+ */
+ for (sym = symtab; --num_syms >= 0; sym++) {
+ if (!sym->st_name)
+ continue;
+
+ GET_SYM(kallsyms_num_syms);
+ GET_SYM(kallsyms_offsets);
+ GET_SYM(kallsyms_relative_base);
+ GET_SYM(kallsyms_names);
+ GET_SYM(kallsyms_markers);
+ GET_SYM(_stext);
+ GET_SYM(_etext);
+ GET_SYM(_sinittext);
+ GET_SYM(_einittext);
+ GET_SYM(__start_orc_unwind_ip);
+ GET_SYM(__stop_orc_unwind_ip);
+ GET_SYM(__start_orc_unwind);
+ GET_SYM(__stop_orc_unwind);
+
+ /* these have to be renamed */
+ if (strcmp("__start___ex_table", strtab + sym->st_name) == 0) {
+ __start___ex_table_addr = sym->st_value;
+ continue;
+ }
+
+ if (strcmp("__stop___ex_table", strtab + sym->st_name) == 0) {
+ __stop___ex_table_addr = sym->st_value;
+ continue;
+ }
+ }
+}
+
+void parse_sections_headers(void *output, Elf64_Ehdr *ehdr, Elf64_Phdr *phdrs)
+{
+ Elf64_Phdr *phdr;
+ Elf64_Shdr *s;
+ Elf64_Shdr *text = NULL;
+ Elf64_Shdr *percpu = NULL;
+ char *secstrings;
+ const char *sname;
+ int num_sections = 0;
+ Elf64_Sym *symtab = NULL;
+ char *strtab = NULL;
+ long num_syms = 0;
+ void *dest;
+ int i;
+ char arg[MAX_FGKASLR_ARG_LENGTH];
+ Elf64_Shdr shdr;
+ unsigned long shnum;
+ unsigned int shstrndx;
+
+ debug_putstr("\nParsing ELF section headers... ");
+
+ /*
+ * Even though fgkaslr may have been disabled, we still
+ * need to parse through the section headers to get the
+ * start and end of the percpu section. This is because
+ * if we were built with CONFIG_FG_KASLR, there are more
+ * relative relocations present in vmlinux.relocs than
+ * just the percpu, and only the percpu relocs need to be
+ * adjusted when using just normal base address kaslr.
+ */
+ if (cmdline_find_option("fgkaslr", arg, sizeof(arg)) == 3 &&
+ !strncmp(arg, "off", 3)) {
+ warn("FG_KASLR disabled on cmdline.");
+ nofgkaslr = 1;
+ }
+
+ /* read the first section header */
+ shnum = ehdr->e_shnum;
+ shstrndx = ehdr->e_shstrndx;
+ if (shnum == SHN_UNDEF || shstrndx == SHN_XINDEX) {
+ memcpy(&shdr, output + ehdr->e_shoff, sizeof(shdr));
+ if (shnum == SHN_UNDEF)
+ shnum = shdr.sh_size;
+ if (shstrndx == SHN_XINDEX)
+ shstrndx = shdr.sh_link;
+ }
+
+ /* we are going to need to allocate space for the section headers */
+ sechdrs = malloc(sizeof(*sechdrs) * shnum);
+ if (!sechdrs)
+ error("Failed to allocate space for shdrs");
+
+ sections = malloc(sizeof(*sections) * shnum);
+ if (!sections)
+ error("Failed to allocate space for section pointers");
+
+ memcpy(sechdrs, output + ehdr->e_shoff,
+ sizeof(*sechdrs) * shnum);
+
+ /* we need to allocate space for the section string table */
+ s = &sechdrs[shstrndx];
+
+ secstrings = malloc(s->sh_size);
+ if (!secstrings)
+ error("Failed to allocate space for shstr");
+
+ memcpy(secstrings, output + s->sh_offset, s->sh_size);
+
+ /*
+ * now we need to walk through the section headers and collect the
+ * sizes of the .text sections to be randomized.
+ */
+ for (i = 0; i < shnum; i++) {
+ s = &sechdrs[i];
+ sname = secstrings + s->sh_name;
+
+ if (s->sh_type == SHT_SYMTAB) {
+ /* only one symtab per image */
+ symtab = malloc(s->sh_size);
+ if (!symtab)
+ error("Failed to allocate space for symtab");
+
+ memcpy(symtab, output + s->sh_offset, s->sh_size);
+ num_syms = s->sh_size/sizeof(*symtab);
+ continue;
+ }
+
+ if (s->sh_type == SHT_STRTAB && (i != ehdr->e_shstrndx)) {
+ strtab = malloc(s->sh_size);
+ if (!strtab)
+ error("Failed to allocate space for strtab");
+
+ memcpy(strtab, output + s->sh_offset, s->sh_size);
+ }
+
+ if (!strcmp(sname, ".text")) {
+ text = s;
+ continue;
+ }
+
+ if (!strcmp(sname, ".data..percpu")) {
+ /* get start addr for later */
+ percpu = s;
+ }
+
+ if (!(s->sh_flags & SHF_ALLOC) ||
+ !(s->sh_flags & SHF_EXECINSTR) ||
+ !(strstarts(sname, ".text")))
+ continue;
+
+ sections[num_sections] = s;
+
+ num_sections++;
+ }
+ sections[num_sections] = NULL;
+ sections_size = num_sections;
+
+ parse_symtab(symtab, strtab, num_syms);
+
+ for (i = 0; i < ehdr->e_phnum; i++) {
+ phdr = &phdrs[i];
+
+ switch (phdr->p_type) {
+ case PT_LOAD:
+ if ((phdr->p_align % 0x200000) != 0)
+ error("Alignment of LOAD segment isn't multiple of 2MB");
+ dest = output;
+ dest += (phdr->p_paddr - LOAD_PHYSICAL_ADDR);
+ if (!nofgkaslr &&
+ (text && (phdr->p_offset == text->sh_offset))) {
+ move_text(num_sections, secstrings, text,
+ output, dest, phdr);
+ } else {
+ if (percpu &&
+ (phdr->p_offset == percpu->sh_offset)) {
+ percpu_start = percpu->sh_addr;
+ percpu_end = percpu_start +
+ phdr->p_filesz;
+ }
+ memmove(dest, output + phdr->p_offset,
+ phdr->p_filesz);
+ }
+ break;
+ default: /* Ignore other PT_* */
+ break;
+ }
+ }
+
+ /* we need to keep the section info to redo relocs */
+ free(secstrings);
+
+ free(phdrs);
+}
+
@@ -39,10 +39,6 @@
#include <generated/utsrelease.h>
#include <asm/efi.h>
-/* Macros used by the included decompressor code below. */
-#define STATIC
-#include <linux/decompress/mm.h>
-
#ifdef CONFIG_X86_5LEVEL
unsigned int __pgtable_l5_enabled;
unsigned int pgdir_shift __ro_after_init = 39;
@@ -897,7 +893,8 @@ void choose_random_location(unsigned long input,
{
unsigned long random_addr, min_addr;
- if (cmdline_find_option_bool("nokaslr")) {
+ nokaslr = cmdline_find_option_bool("nokaslr");
+ if (nokaslr) {
warn("KASLR disabled: 'nokaslr' on cmdline.");
return;
}
@@ -26,9 +26,6 @@
* it is not safe to place pointers in static structures.
*/
-/* Macros used by the included decompressor code below. */
-#define STATIC static
-
/*
* Use normal definitions of mem*() from string.c. There are already
* included header files which expect a definition of memset() and by
@@ -49,6 +46,8 @@ struct boot_params *boot_params;
memptr free_mem_ptr;
memptr free_mem_end_ptr;
+unsigned long malloc_ptr;
+int malloc_count;
static char *vidmem;
static int vidport;
@@ -203,10 +202,20 @@ static void handle_relocations(void *output, unsigned long output_len,
if (IS_ENABLED(CONFIG_X86_64))
delta = virt_addr - LOAD_PHYSICAL_ADDR;
- if (!delta) {
- debug_putstr("No relocation needed... ");
- return;
+ /*
+ * it is possible to have delta be zero and
+ * still have enabled fg kaslr. We need to perform relocations
+ * for fgkaslr regardless of whether the base address has moved.
+ */
+ if (!IS_ENABLED(CONFIG_FG_KASLR) || nokaslr) {
+ if (!delta) {
+ debug_putstr("No relocation needed... ");
+ return;
+ }
}
+
+ pre_relocations_cleanup(map);
+
debug_putstr("Performing relocations... ");
/*
@@ -230,35 +239,106 @@ static void handle_relocations(void *output, unsigned long output_len,
*/
for (reloc = output + output_len - sizeof(*reloc); *reloc; reloc--) {
long extended = *reloc;
+ long value;
+
+ /*
+ * if using fgkaslr, we might have moved the address
+ * of the relocation. Check it to see if it needs adjusting
+ * from the original address.
+ */
+ (void) adjust_address(&extended);
+
extended += map;
ptr = (unsigned long)extended;
if (ptr < min_addr || ptr > max_addr)
error("32-bit relocation outside of kernel!\n");
- *(uint32_t *)ptr += delta;
+ value = *(int32_t *)ptr;
+
+ /*
+ * If using fgkaslr, the value of the relocation
+ * might need to be changed because it referred
+ * to an address that has moved.
+ */
+ adjust_address(&value);
+
+ value += delta;
+
+ *(uint32_t *)ptr = value;
}
#ifdef CONFIG_X86_64
while (*--reloc) {
long extended = *reloc;
+ long value;
+ long oldvalue;
+ Elf64_Shdr *s;
+
+ /*
+ * if using fgkaslr, we might have moved the address
+ * of the relocation. Check it to see if it needs adjusting
+ * from the original address.
+ */
+ s = adjust_address(&extended);
+
extended += map;
ptr = (unsigned long)extended;
if (ptr < min_addr || ptr > max_addr)
error("inverse 32-bit relocation outside of kernel!\n");
- *(int32_t *)ptr -= delta;
+ value = *(int32_t *)ptr;
+ oldvalue = value;
+
+ /*
+ * If using fgkaslr, these relocs will contain
+ * relative offsets which might need to be
+ * changed because it referred
+ * to an address that has moved.
+ */
+ adjust_relative_offset(*reloc, &value, s);
+
+ /*
+ * only percpu symbols need to have their values adjusted for
+ * base address kaslr since relative offsets within the .text
+ * and .text.* sections are ok wrt each other.
+ */
+ if (is_percpu_addr(*reloc, oldvalue))
+ value -= delta;
+
+ *(int32_t *)ptr = value;
}
for (reloc--; *reloc; reloc--) {
long extended = *reloc;
+ long value;
+
+ /*
+ * if using fgkaslr, we might have moved the address
+ * of the relocation. Check it to see if it needs adjusting
+ * from the original address.
+ */
+ (void) adjust_address(&extended);
+
extended += map;
ptr = (unsigned long)extended;
if (ptr < min_addr || ptr > max_addr)
error("64-bit relocation outside of kernel!\n");
- *(uint64_t *)ptr += delta;
+ value = *(int64_t *)ptr;
+
+ /*
+ * If using fgkaslr, the value of the relocation
+ * might need to be changed because it referred
+ * to an address that has moved.
+ */
+ (void) adjust_address(&value);
+
+ value += delta;
+
+ *(uint64_t *)ptr = value;
}
+ post_relocations_cleanup(map);
#endif
}
#else
@@ -296,6 +376,15 @@ static void parse_elf(void *output)
memcpy(phdrs, output + ehdr.e_phoff, sizeof(*phdrs) * ehdr.e_phnum);
+ if (IS_ENABLED(CONFIG_FG_KASLR)) {
+ if (!nokaslr) {
+ parse_sections_headers(output, &ehdr, phdrs);
+ return;
+ } else {
+ warn("FG_KASLR disabled: 'nokaslr' on cmdline.");
+ }
+ }
+
for (i = 0; i < ehdr.e_phnum; i++) {
phdr = &phdrs[i];
@@ -39,7 +39,12 @@
/* misc.c */
extern memptr free_mem_ptr;
extern memptr free_mem_end_ptr;
+#define STATIC
+#define STATIC_RW_DATA extern
+#include <linux/decompress/mm.h>
+
extern struct boot_params *boot_params;
+extern int nokaslr;
void __putstr(const char *s);
void __puthex(unsigned long value);
#define error_putstr(__x) __putstr(__x)
@@ -74,6 +79,32 @@ struct mem_vector {
unsigned long long size;
};
+#ifdef CONFIG_X86_64
+#define Elf_Ehdr Elf64_Ehdr
+#define Elf_Phdr Elf64_Phdr
+#define Elf_Shdr Elf64_Shdr
+#else
+#define Elf_Ehdr Elf32_Ehdr
+#define Elf_Phdr Elf32_Phdr
+#define Elf_Shdr Elf32_Shdr
+#endif
+
+#if CONFIG_FG_KASLR
+void parse_sections_headers(void *output, Elf_Ehdr *ehdr, Elf_Phdr *phdrs);
+void pre_relocations_cleanup(unsigned long map);
+void post_relocations_cleanup(unsigned long map);
+Elf_Shdr *adjust_address(long *address);
+void adjust_relative_offset(long pc, long *value, Elf_Shdr *section);
+bool is_percpu_addr(long pc, long offset);
+#else
+static inline void parse_sections_headers(void *output, Elf_Ehdr *ehdr, Elf_Phdr *phdrs) { }
+static inline void pre_relocations_cleanup(unsigned long map) { }
+static inline void post_relocations_cleanup(unsigned long map) { }
+static inline Elf_Shdr *adjust_address(long *address) { return NULL; }
+static inline void adjust_relative_offset(long pc, long *value, Elf_Shdr *section) { }
+static inline bool is_percpu_addr(long pc, long offset) { return true; }
+#endif /* CONFIG_FG_KASLR */
+
#if CONFIG_RANDOMIZE_BASE
/* kaslr.c */
void choose_random_location(unsigned long input,
new file mode 100644
@@ -0,0 +1,12 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * utils.c
+ *
+ * This contains various libraries that are needed for fgkaslr
+ */
+#define __DISABLE_EXPORTS
+#define _LINUX_KPROBES_H
+#define NOKPROBE_SYMBOL(fname)
+#include "../../../../lib/sort.c"
+#include "../../../../lib/bsearch.c"
+
new file mode 100644
@@ -0,0 +1,18 @@
+kallsyms_offsets
+kallsyms_addresses
+kallsyms_num_syms
+kallsyms_relative_base
+kallsyms_names
+kallsyms_token_table
+kallsyms_token_index
+kallsyms_markers
+__start___ex_table
+__stop___ex_table
+_sinittext
+_einittext
+_stext
+_etext
+__start_orc_unwind_ip
+__stop_orc_unwind_ip
+__stop_orc_unwind
+__start_orc_unwind
@@ -26,8 +26,19 @@
#ifdef CONFIG_KERNEL_BZIP2
# define BOOT_HEAP_SIZE 0x400000
-#else /* !CONFIG_KERNEL_BZIP2 */
-# define BOOT_HEAP_SIZE 0x10000
+#elif CONFIG_FG_KASLR
+/*
+ * We need extra boot heap when using fgkaslr because we make a copy
+ * of the original decompressed kernel to avoid issues with writing
+ * over ourselves when shuffling the sections. We also need extra
+ * space for resorting kallsyms after shuffling. This value could
+ * be decreased if free() would release memory properly, or if we
+ * could avoid the kernel copy. It would need to be increased if we
+ * find additional tables that need to be resorted.
+ */
+# define BOOT_HEAP_SIZE 0x4000000
+#else /* !CONFIG_KERNEL_BZIP2 && !CONFIG_FG_KASLR */
+# define BOOT_HEAP_SIZE 0x10000
#endif
#ifdef CONFIG_X86_64
@@ -298,6 +298,7 @@ typedef struct elf64_phdr {
#define SHN_LIVEPATCH 0xff20
#define SHN_ABS 0xfff1
#define SHN_COMMON 0xfff2
+#define SHN_XINDEX 0xffff
#define SHN_HIRESERVE 0xffff
typedef struct elf32_shdr {
At boot time, find all the function sections that have separate .text sections, shuffle them, and then copy them to new locations. Adjust any relocations accordingly. Signed-off-by: Kristen Carlson Accardi <kristen@linux.intel.com> --- Documentation/security/fgkaslr.rst | 151 +++++ Documentation/security/index.rst | 1 + arch/x86/boot/compressed/Makefile | 3 + arch/x86/boot/compressed/fgkaslr.c | 809 +++++++++++++++++++++++ arch/x86/boot/compressed/kaslr.c | 7 +- arch/x86/boot/compressed/misc.c | 107 ++- arch/x86/boot/compressed/misc.h | 31 + arch/x86/boot/compressed/utils.c | 12 + arch/x86/boot/compressed/vmlinux.symbols | 18 + arch/x86/include/asm/boot.h | 15 +- include/uapi/linux/elf.h | 1 + 11 files changed, 1139 insertions(+), 16 deletions(-) create mode 100644 Documentation/security/fgkaslr.rst create mode 100644 arch/x86/boot/compressed/fgkaslr.c create mode 100644 arch/x86/boot/compressed/utils.c create mode 100644 arch/x86/boot/compressed/vmlinux.symbols