[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Date: Tue, 23 Jun 2020 10:23:25 -0700
From: Kristen Carlson Accardi <kristen@...ux.intel.com>
To: keescook@...omium.org,
tglx@...utronix.de,
mingo@...hat.com,
bp@...en8.de,
Jonathan Corbet <corbet@....net>,
x86@...nel.org,
"H. Peter Anvin" <hpa@...or.com>
Cc: arjan@...ux.intel.com,
linux-kernel@...r.kernel.org,
kernel-hardening@...ts.openwall.com,
rick.p.edgecombe@...el.com,
Kristen Carlson Accardi <kristen@...ux.intel.com>,
Tony Luck <tony.luck@...el.com>,
linux-doc@...r.kernel.org
Subject: [PATCH v3 08/10] x86: Add support for function granular KASLR
This commit contains the changes required to re-layout the kernel text
sections generated by -ffunction-sections shortly after decompression.
Documentation of the feature is also added.
After decompression, the decompressed image's elf headers are parsed.
In order to manually update certain data structures that are built with
relative offsets during the kernel build process, certain symbols are
not stripped by objdump and their location is retained in the elf symbol
tables. These addresses are saved.
If the image was built with -ffunction-sections, there will be ELF section
headers present which contain information about the address range of each
section. Anything that is not broken out into function sections (i.e. is
consolidated into .text) is left in it's original location, but any other
executable section which begins with ".text." is located and shuffled
randomly within the remaining text segment address range.
After the sections have been copied to their new locations, but before
relocations have been applied, the kallsyms tables must be updated to
reflect the new symbol locations. Because it is expected that these tables
will be sorted by address, the kallsyms tables will need to be sorted
after the update.
When applying relocations, the address of the relocation needs to be
adjusted by the offset from the original location of the section that was
randomized to it's new location. In addition, if a value at that relocation
was a location in the text segment that was randomized, it's value will be
adjusted to a new location.
After relocations have been applied, the exception table must be updated
with with new symbol locations, and then re-sorted by the new address. The
orc table will have been updated as part of applying relocations, but since
it is expected to be sorted by address, it will need to be resorted.
Signed-off-by: Kristen Carlson Accardi <kristen@...ux.intel.com>
Reviewed-by: Tony Luck <tony.luck@...el.com>
Tested-by: Tony Luck <tony.luck@...el.com>
---
Documentation/security/fgkaslr.rst | 173 +++++
Documentation/security/index.rst | 1 +
arch/x86/boot/compressed/Makefile | 2 +
arch/x86/boot/compressed/fgkaslr.c | 812 +++++++++++++++++++++++
arch/x86/boot/compressed/misc.c | 154 ++++-
arch/x86/boot/compressed/misc.h | 28 +
arch/x86/boot/compressed/utils.c | 12 +
arch/x86/boot/compressed/vmlinux.symbols | 17 +
arch/x86/include/asm/boot.h | 15 +-
include/uapi/linux/elf.h | 1 +
10 files changed, 1187 insertions(+), 28 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
diff --git a/Documentation/security/fgkaslr.rst b/Documentation/security/fgkaslr.rst
new file mode 100644
index 000000000000..9478b1298ae8
--- /dev/null
+++ b/Documentation/security/fgkaslr.rst
@@ -0,0 +1,173 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+=====================================================================
+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. The term "fgkaslr" is used in this document to refer to the
+technique of function reordering when used with KASLR, as well as finer grained
+KASLR in general.
+
+The objective of this patch set is to improve a technology that is already
+merged into the kernel (KASLR). This code will not prevent all code reuse
+attacks, and should be considered as one of several tools that can be used.
+
+Implementation Details
+======================
+
+The over-arching objective of the fgkaslr implementation is incremental
+improvement over the existing KASLR algorithm. 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 had an option to place functions into individual .text sections
+for many years now (-ffunction-sections). This option is used to implement
+function reordering at load time. The final compiled vmlinux retains all the
+section headers, which can be used to help find the address ranges of each
+function. Using this information and an expanded table of relocation addresses,
+individual text sections can be shuffled immediately after decompression.
+Some data tables inside the kernel that have assumptions about order
+require sorting after the update. In order to modify these tables,
+a few key symbols from the objcopy symbol stripping process are preserved
+for use after shuffling the text segments. Any special input sections which are
+defined by the kernel build process and collected into the .text output
+segment are left unmodified and will still be present inside the .text segment,
+unrandomized other than normal base address randomization.
+
+Load time
+---------
+
+The boot kernel was modified to parse the vmlinux elf file after
+decompression to check for symbols for modifying data tables, and to
+look for any .text.* sections to randomize. The sections are then shuffled,
+and tables are 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 the new layout, symbols reported through /proc/kallsyms will
+be sorted by name alphabetically rather than by address.
+
+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. Some workloads perform significantly worse under FGKASLR,
+while others stay the same or even improve. In general, it will depend on the
+code flow whether or not finer grained KASLR will impact a workload, and how
+the underlying code was designed. Because the layout changes per boot, each
+time a system is rebooted the performance of a workload may change.
+
+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%.
+
+Memory Usage
+============
+
+fgkaslr increases the amount of heap that is required at boot time,
+although this extra memory is released when the kernel has finished
+decompression. As a result, it may not be appropriate to use this feature
+on systems without much memory.
+
+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``
+
+fgkaslr for the kernel 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.
+
+Although fgkaslr for the kernel is only supported for the X86_64 architecture,
+it is possible to use fgkaslr with modules on other architectures. To enable
+this feature, select the following config option:
+
+``CONFIG_MODULE_FG_KASLR``
+
+This option is selected automatically for X86_64 when CONFIG_FG_KASLR is set.
+
+Disabling
+=========
+
+Disabling normal kaslr using the nokaslr command line option also disables
+fgkaslr. In addtion, it is possible to disable fgkaslr separately by booting
+with fgkaslr=off on the commandline.
+
+Further Information
+===================
+
+There are a lot of academic papers which explore finer grained ASLR.
+This paper in particular contributed significantly to the implementation design.
+
+Selfrando: Securing the Tor Browser against De-anonymization Exploits,
+M. Conti, S. Crane, T. Frassetto, et al.
+
+For more information on how function layout impacts performance, see:
+
+Optimizing Function Placement for Large-Scale Data-Center Applications,
+G. Ottoni, B. Maher
+
diff --git a/Documentation/security/index.rst b/Documentation/security/index.rst
index 8129405eb2cc..19677beb33d4 100644
--- a/Documentation/security/index.rst
+++ b/Documentation/security/index.rst
@@ -7,6 +7,7 @@ Security Documentation
credentials
IMA-templates
+ fgkaslr
keys/index
lsm
lsm-development
diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile
index c17b1c8ec82c..1508995dc2ed 100644
--- a/arch/x86/boot/compressed/Makefile
+++ b/arch/x86/boot/compressed/Makefile
@@ -82,6 +82,7 @@ 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 $(obj)/fgkaslr.o
ifdef CONFIG_X86_64
vmlinux-objs-$(CONFIG_RANDOMIZE_BASE) += $(obj)/kaslr_64.o
vmlinux-objs-y += $(obj)/mem_encrypt.o
@@ -122,6 +123,7 @@ OBJCOPYFLAGS_vmlinux.bin := -R .comment -S
ifdef CONFIG_FG_KASLR
RELOCS_ARGS += --fg-kaslr
+ OBJCOPYFLAGS += --keep-symbols=$(srctree)/$(src)/vmlinux.symbols
endif
$(obj)/vmlinux.bin: vmlinux FORCE
diff --git a/arch/x86/boot/compressed/fgkaslr.c b/arch/x86/boot/compressed/fgkaslr.c
new file mode 100644
index 000000000000..e5f4503fafa3
--- /dev/null
+++ b/arch/x86/boot/compressed/fgkaslr.c
@@ -0,0 +1,812 @@
+// 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
+static 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 addr_kallsyms_names;
+static long addr_kallsyms_offsets;
+static long addr_kallsyms_num_syms;
+static long addr_kallsyms_relative_base;
+static long addr_kallsyms_markers;
+static long addr___start___ex_table;
+static long addr___stop___ex_table;
+static long addr__stext;
+static long addr__etext;
+static long addr__sinittext;
+static long addr__einittext;
+static long addr___start_orc_unwind_ip;
+static long addr___stop_orc_unwind_ip;
+static long addr___start_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];
+};
+
+static struct kallsyms_name *names_table;
+
+static struct orc_entry *cur_orc_table;
+static int *cur_orc_ip_table;
+
+/* Array of pointers to sections headers for randomized sections */
+Elf_Shdr **sections;
+
+/* Number of elements in the randomized section header array (sections) */
+static int sections_size;
+
+/* Array of all section headers, randomized or otherwise */
+static Elf_Shdr *sechdrs;
+
+static bool is_text(long addr)
+{
+ if ((addr >= addr__stext && addr < addr__etext) ||
+ (addr >= addr__sinittext && addr < 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;
+ Elf_Shdr *s = *(Elf_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.
+ */
+Elf_Shdr *adjust_address(long *address)
+{
+ Elf_Shdr **s;
+ Elf_Shdr *shdr;
+
+ if (nofgkaslr)
+ return NULL;
+
+ s = bsearch((const void *)*address, sections, sections_size, sizeof(*s),
+ cmp_section_addr);
+ if (s) {
+ shdr = *s;
+ *address += shdr->sh_offset;
+ return shdr;
+ }
+
+ return NULL;
+}
+
+void adjust_relative_offset(long pc, long *value, Elf_Shdr *section)
+{
+ Elf_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)
+ *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)
+ *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;
+
+ /* 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) {
+ 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...\n");
+
+ num_syms = *(int *)(addr_kallsyms_num_syms + map);
+ base = (int *)(addr_kallsyms_offsets + map);
+ relative_base = *(unsigned long *)(addr_kallsyms_relative_base + map);
+ markers_addr = (unsigned int *)(addr_kallsyms_markers + map);
+ names = (u8 *)(addr_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);
+}
+
+/*
+ * We need to include this file here rather than in utils.c because
+ * some of the helper functions in extable.c are used to update
+ * the extable below and are defined as "static" in extable.c
+ */
+#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 *)(addr___start___ex_table + map);
+ struct exception_table_entry *stop_ex_table =
+ (struct exception_table_entry *)(addr___stop___ex_table + map);
+ int num_entries =
+ (addr___stop___ex_table - addr___start___ex_table) /
+ sizeof(struct exception_table_entry);
+ int i;
+
+ debug_putstr("\nUpdating exception table...");
+ 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;
+ Elf_Shdr *s;
+
+ /* check each address to see if it needs adjusting */
+ addr = insn - map;
+ s = adjust_address(&addr);
+ if (s)
+ start_ex_table[i].insn += s->sh_offset;
+
+ addr = fixup - map;
+ s = adjust_address(&addr);
+ if (s)
+ start_ex_table[i].fixup += s->sh_offset;
+
+ addr = handler - map;
+ s = adjust_address(&addr);
+ if (s)
+ 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 *)(addr___start___ex_table + map);
+ struct exception_table_entry *stop_ex_table =
+ (struct exception_table_entry *)(addr___stop___ex_table + map);
+
+ debug_putstr("\nRe-sorting exception table...");
+
+ 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 =
+ (addr___stop_orc_unwind_ip - addr___start_orc_unwind_ip) / sizeof(int);
+
+ cur_orc_ip_table = (int *)(addr___start_orc_unwind_ip + map);
+ cur_orc_table = (struct orc_entry *)(addr___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, Elf_Shdr *text,
+ void *source, void *dest, Elf64_Phdr *phdr)
+{
+ unsigned long adjusted_addr;
+ int copy_bytes;
+ void *stash;
+ Elf_Shdr **sorted_sections;
+ int *index_list;
+ int i, j;
+
+ 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 (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 (j = 0; j < num_sections; j++) {
+ unsigned long aligned_addr;
+ Elf_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;
+ memset(dest, 0xcc, pad_bytes);
+
+ 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 (!addr_ ## name) { \
+ if (strcmp(#name, strtab + sym->st_name) == 0) {\
+ addr_ ## name = sym->st_value; \
+ continue; \
+ } \
+ } \
+ } while (0)
+
+static void parse_symtab(Elf64_Sym *symtab, char *strtab, long num_syms)
+{
+ Elf64_Sym *sym;
+
+ if (!symtab || !strtab)
+ 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(__start___ex_table);
+ GET_SYM(__stop___ex_table);
+ }
+}
+
+void layout_randomized_image(void *output, Elf64_Ehdr *ehdr, Elf64_Phdr *phdrs)
+{
+ Elf64_Phdr *phdr;
+ Elf_Shdr *s;
+ Elf_Shdr *text = NULL;
+ Elf_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];
+ Elf_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 */
+ if (symtab)
+ error("Unexpected duplicate symtab");
+
+ 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) {
+ if (strtab)
+ error("Unexpected duplicate strtab");
+
+ 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")) {
+ if (text)
+ error("Unexpected duplicate .text section");
+
+ text = s;
+ continue;
+ }
+
+ if (!strcmp(sname, ".data..percpu")) {
+ /* get start addr for later */
+ percpu = s;
+ continue;
+ }
+
+ 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);
+}
+
diff --git a/arch/x86/boot/compressed/misc.c b/arch/x86/boot/compressed/misc.c
index a55a4ec48422..7667415417dc 100644
--- a/arch/x86/boot/compressed/misc.c
+++ b/arch/x86/boot/compressed/misc.c
@@ -204,10 +204,21 @@ 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) ||
+ cmdline_find_option_bool("nokaslr")) {
+ if (!delta) {
+ debug_putstr("No relocation needed... ");
+ return;
+ }
}
+
+ pre_relocations_cleanup(map);
+
debug_putstr("Performing relocations... ");
/*
@@ -231,35 +242,106 @@ 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.
+ */
+ 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.
+ */
+ 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.
+ */
+ adjust_address(&value);
+
+ value += delta;
+
+ *(uint64_t *)ptr = value;
}
+ post_relocations_cleanup(map);
#endif
}
#else
@@ -268,6 +350,35 @@ static inline void handle_relocations(void *output, unsigned long output_len,
{ }
#endif
+static void layout_image(void *output, Elf_Ehdr *ehdr, Elf_Phdr *phdrs)
+{
+ int i;
+ void *dest;
+ Elf_Phdr *phdr;
+
+ for (i = 0; i < ehdr->e_phnum; i++) {
+ phdr = &phdrs[i];
+
+ switch (phdr->p_type) {
+ case PT_LOAD:
+#ifdef CONFIG_X86_64
+ if ((phdr->p_align % 0x200000) != 0)
+ error("Alignment of LOAD segment isn't multiple of 2MB");
+#endif
+#ifdef CONFIG_RELOCATABLE
+ dest = output;
+ dest += (phdr->p_paddr - LOAD_PHYSICAL_ADDR);
+#else
+ dest = (void *)(phdr->p_paddr);
+#endif
+ memmove(dest, output + phdr->p_offset, phdr->p_filesz);
+ break;
+ default: /* Ignore other PT_* */
+ break;
+ }
+ }
+}
+
static void parse_elf(void *output)
{
#ifdef CONFIG_X86_64
@@ -279,6 +390,7 @@ static void parse_elf(void *output)
#endif
void *dest;
int i;
+ int nokaslr;
memcpy(&ehdr, output, sizeof(ehdr));
if (ehdr.e_ident[EI_MAG0] != ELFMAG0 ||
@@ -289,6 +401,12 @@ static void parse_elf(void *output)
return;
}
+ if (IS_ENABLED(CONFIG_FG_KASLR)) {
+ nokaslr = cmdline_find_option_bool("nokaslr");
+ if (nokaslr)
+ warn("FG_KASLR disabled: 'nokaslr' on cmdline.");
+ }
+
debug_putstr("Parsing ELF... ");
phdrs = malloc(sizeof(*phdrs) * ehdr.e_phnum);
@@ -297,26 +415,10 @@ static void parse_elf(void *output)
memcpy(phdrs, output + ehdr.e_phoff, sizeof(*phdrs) * ehdr.e_phnum);
- for (i = 0; i < ehdr.e_phnum; i++) {
- phdr = &phdrs[i];
-
- switch (phdr->p_type) {
- case PT_LOAD:
-#ifdef CONFIG_X86_64
- if ((phdr->p_align % 0x200000) != 0)
- error("Alignment of LOAD segment isn't multiple of 2MB");
-#endif
-#ifdef CONFIG_RELOCATABLE
- dest = output;
- dest += (phdr->p_paddr - LOAD_PHYSICAL_ADDR);
-#else
- dest = (void *)(phdr->p_paddr);
-#endif
- memmove(dest, output + phdr->p_offset, phdr->p_filesz);
- break;
- default: /* Ignore other PT_* */ break;
- }
- }
+ if (IS_ENABLED(CONFIG_FG_KASLR) && !nokaslr)
+ layout_randomized_image(output, &ehdr, phdrs);
+ else
+ layout_image(output, &ehdr, phdrs);
free(phdrs);
}
diff --git a/arch/x86/boot/compressed/misc.h b/arch/x86/boot/compressed/misc.h
index d2ec7c745cfa..86a5f00b018f 100644
--- a/arch/x86/boot/compressed/misc.h
+++ b/arch/x86/boot/compressed/misc.h
@@ -80,6 +80,34 @@ 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 layout_randomized_image(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 layout_randomized_image(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,
diff --git a/arch/x86/boot/compressed/utils.c b/arch/x86/boot/compressed/utils.c
new file mode 100644
index 000000000000..ceefc58d7c71
--- /dev/null
+++ b/arch/x86/boot/compressed/utils.c
@@ -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"
+
diff --git a/arch/x86/boot/compressed/vmlinux.symbols b/arch/x86/boot/compressed/vmlinux.symbols
new file mode 100644
index 000000000000..cc86e79a2a3d
--- /dev/null
+++ b/arch/x86/boot/compressed/vmlinux.symbols
@@ -0,0 +1,17 @@
+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
+__start_orc_unwind
diff --git a/arch/x86/include/asm/boot.h b/arch/x86/include/asm/boot.h
index 680c320363db..6918d33eb5ef 100644
--- a/arch/x86/include/asm/boot.h
+++ b/arch/x86/include/asm/boot.h
@@ -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
diff --git a/include/uapi/linux/elf.h b/include/uapi/linux/elf.h
index c6dd0215482e..4ef6360bd18c 100644
--- a/include/uapi/linux/elf.h
+++ b/include/uapi/linux/elf.h
@@ -299,6 +299,7 @@ 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 {
--
2.20.1
Powered by blists - more mailing lists
Confused about mailing lists and their use?
Read about mailing lists on Wikipedia
and check out these
guidelines on proper formatting of your messages.
