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qemu-e2k/hw/i386/multiboot.c
Prasad J Pandit ed4f86e8b6 multiboot: validate multiboot header address values 
While loading kernel via multiboot-v1 image, (flags & 0x00010000)
indicates that multiboot header contains valid addresses to load
the kernel image. These addresses are used to compute kernel
size and kernel text offset in the OS image. Validate these
address values to avoid an OOB access issue.

This is CVE-2017-14167.

Reported-by: Thomas Garnier <thgarnie@google.com>
Signed-off-by: Prasad J Pandit <pjp@fedoraproject.org>
Message-Id: <20170907063256.7418-1-ppandit@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
2017-09-19 14:09:33 +02:00

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/*
* QEMU PC System Emulator
*
* Copyright (c) 2003-2004 Fabrice Bellard
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
* THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
* THE SOFTWARE.
*/
#include "qemu/osdep.h"
#include "qemu-common.h"
#include "cpu.h"
#include "hw/hw.h"
#include "hw/nvram/fw_cfg.h"
#include "multiboot.h"
#include "hw/loader.h"
#include "elf.h"
#include "sysemu/sysemu.h"
/* Show multiboot debug output */
//#define DEBUG_MULTIBOOT
#ifdef DEBUG_MULTIBOOT
#define mb_debug(a...) fprintf(stderr, ## a)
#else
#define mb_debug(a...)
#endif
#define MULTIBOOT_STRUCT_ADDR 0x9000
#if MULTIBOOT_STRUCT_ADDR > 0xf0000
#error multiboot struct needs to fit in 16 bit real mode
#endif
enum {
/* Multiboot info */
MBI_FLAGS = 0,
MBI_MEM_LOWER = 4,
MBI_MEM_UPPER = 8,
MBI_BOOT_DEVICE = 12,
MBI_CMDLINE = 16,
MBI_MODS_COUNT = 20,
MBI_MODS_ADDR = 24,
MBI_MMAP_ADDR = 48,
MBI_BOOTLOADER = 64,
MBI_SIZE = 88,
/* Multiboot modules */
MB_MOD_START = 0,
MB_MOD_END = 4,
MB_MOD_CMDLINE = 8,
MB_MOD_SIZE = 16,
/* Region offsets */
ADDR_E820_MAP = MULTIBOOT_STRUCT_ADDR + 0,
ADDR_MBI = ADDR_E820_MAP + 0x500,
/* Multiboot flags */
MULTIBOOT_FLAGS_MEMORY = 1 << 0,
MULTIBOOT_FLAGS_BOOT_DEVICE = 1 << 1,
MULTIBOOT_FLAGS_CMDLINE = 1 << 2,
MULTIBOOT_FLAGS_MODULES = 1 << 3,
MULTIBOOT_FLAGS_MMAP = 1 << 6,
MULTIBOOT_FLAGS_BOOTLOADER = 1 << 9,
};
typedef struct {
/* buffer holding kernel, cmdlines and mb_infos */
void *mb_buf;
/* address in target */
hwaddr mb_buf_phys;
/* size of mb_buf in bytes */
unsigned mb_buf_size;
/* offset of mb-info's in bytes */
hwaddr offset_mbinfo;
/* offset in buffer for cmdlines in bytes */
hwaddr offset_cmdlines;
/* offset in buffer for bootloader name in bytes */
hwaddr offset_bootloader;
/* offset of modules in bytes */
hwaddr offset_mods;
/* available slots for mb modules infos */
int mb_mods_avail;
/* currently used slots of mb modules */
int mb_mods_count;
} MultibootState;
const char *bootloader_name = "qemu";
static uint32_t mb_add_cmdline(MultibootState *s, const char *cmdline)
{
hwaddr p = s->offset_cmdlines;
char *b = (char *)s->mb_buf + p;
memcpy(b, cmdline, strlen(cmdline) + 1);
s->offset_cmdlines += strlen(b) + 1;
return s->mb_buf_phys + p;
}
static uint32_t mb_add_bootloader(MultibootState *s, const char *bootloader)
{
hwaddr p = s->offset_bootloader;
char *b = (char *)s->mb_buf + p;
memcpy(b, bootloader, strlen(bootloader) + 1);
s->offset_bootloader += strlen(b) + 1;
return s->mb_buf_phys + p;
}
static void mb_add_mod(MultibootState *s,
hwaddr start, hwaddr end,
hwaddr cmdline_phys)
{
char *p;
assert(s->mb_mods_count < s->mb_mods_avail);
p = (char *)s->mb_buf + s->offset_mbinfo + MB_MOD_SIZE * s->mb_mods_count;
stl_p(p + MB_MOD_START, start);
stl_p(p + MB_MOD_END, end);
stl_p(p + MB_MOD_CMDLINE, cmdline_phys);
mb_debug("mod%02d: "TARGET_FMT_plx" - "TARGET_FMT_plx"\n",
s->mb_mods_count, start, end);
s->mb_mods_count++;
}
int load_multiboot(FWCfgState *fw_cfg,
FILE *f,
const char *kernel_filename,
const char *initrd_filename,
const char *kernel_cmdline,
int kernel_file_size,
uint8_t *header)
{
int i, is_multiboot = 0;
uint32_t flags = 0;
uint32_t mh_entry_addr;
uint32_t mh_load_addr;
uint32_t mb_kernel_size;
MultibootState mbs;
uint8_t bootinfo[MBI_SIZE];
uint8_t *mb_bootinfo_data;
uint32_t cmdline_len;
/* Ok, let's see if it is a multiboot image.
The header is 12x32bit long, so the latest entry may be 8192 - 48. */
for (i = 0; i < (8192 - 48); i += 4) {
if (ldl_p(header+i) == 0x1BADB002) {
uint32_t checksum = ldl_p(header+i+8);
flags = ldl_p(header+i+4);
checksum += flags;
checksum += (uint32_t)0x1BADB002;
if (!checksum) {
is_multiboot = 1;
break;
}
}
}
if (!is_multiboot)
return 0; /* no multiboot */
mb_debug("qemu: I believe we found a multiboot image!\n");
memset(bootinfo, 0, sizeof(bootinfo));
memset(&mbs, 0, sizeof(mbs));
if (flags & 0x00000004) { /* MULTIBOOT_HEADER_HAS_VBE */
fprintf(stderr, "qemu: multiboot knows VBE. we don't.\n");
}
if (!(flags & 0x00010000)) { /* MULTIBOOT_HEADER_HAS_ADDR */
uint64_t elf_entry;
uint64_t elf_low, elf_high;
int kernel_size;
fclose(f);
if (((struct elf64_hdr*)header)->e_machine == EM_X86_64) {
fprintf(stderr, "Cannot load x86-64 image, give a 32bit one.\n");
exit(1);
}
kernel_size = load_elf(kernel_filename, NULL, NULL, &elf_entry,
&elf_low, &elf_high, 0, I386_ELF_MACHINE,
0, 0);
if (kernel_size < 0) {
fprintf(stderr, "Error while loading elf kernel\n");
exit(1);
}
mh_load_addr = elf_low;
mb_kernel_size = elf_high - elf_low;
mh_entry_addr = elf_entry;
mbs.mb_buf = g_malloc(mb_kernel_size);
if (rom_copy(mbs.mb_buf, mh_load_addr, mb_kernel_size) != mb_kernel_size) {
fprintf(stderr, "Error while fetching elf kernel from rom\n");
exit(1);
}
mb_debug("qemu: loading multiboot-elf kernel (%#x bytes) with entry %#zx\n",
mb_kernel_size, (size_t)mh_entry_addr);
} else {
/* Valid if mh_flags sets MULTIBOOT_HEADER_HAS_ADDR. */
uint32_t mh_header_addr = ldl_p(header+i+12);
uint32_t mh_load_end_addr = ldl_p(header+i+20);
uint32_t mh_bss_end_addr = ldl_p(header+i+24);
mh_load_addr = ldl_p(header+i+16);
if (mh_header_addr < mh_load_addr) {
fprintf(stderr, "invalid mh_load_addr address\n");
exit(1);
}
uint32_t mb_kernel_text_offset = i - (mh_header_addr - mh_load_addr);
uint32_t mb_load_size = 0;
mh_entry_addr = ldl_p(header+i+28);
if (mh_load_end_addr) {
if (mh_bss_end_addr < mh_load_addr) {
fprintf(stderr, "invalid mh_bss_end_addr address\n");
exit(1);
}
mb_kernel_size = mh_bss_end_addr - mh_load_addr;
if (mh_load_end_addr < mh_load_addr) {
fprintf(stderr, "invalid mh_load_end_addr address\n");
exit(1);
}
mb_load_size = mh_load_end_addr - mh_load_addr;
} else {
if (kernel_file_size < mb_kernel_text_offset) {
fprintf(stderr, "invalid kernel_file_size\n");
exit(1);
}
mb_kernel_size = kernel_file_size - mb_kernel_text_offset;
mb_load_size = mb_kernel_size;
}
/* Valid if mh_flags sets MULTIBOOT_HEADER_HAS_VBE.
uint32_t mh_mode_type = ldl_p(header+i+32);
uint32_t mh_width = ldl_p(header+i+36);
uint32_t mh_height = ldl_p(header+i+40);
uint32_t mh_depth = ldl_p(header+i+44); */
mb_debug("multiboot: mh_header_addr = %#x\n", mh_header_addr);
mb_debug("multiboot: mh_load_addr = %#x\n", mh_load_addr);
mb_debug("multiboot: mh_load_end_addr = %#x\n", mh_load_end_addr);
mb_debug("multiboot: mh_bss_end_addr = %#x\n", mh_bss_end_addr);
mb_debug("qemu: loading multiboot kernel (%#x bytes) at %#x\n",
mb_load_size, mh_load_addr);
mbs.mb_buf = g_malloc(mb_kernel_size);
fseek(f, mb_kernel_text_offset, SEEK_SET);
if (fread(mbs.mb_buf, 1, mb_load_size, f) != mb_load_size) {
fprintf(stderr, "fread() failed\n");
exit(1);
}
memset(mbs.mb_buf + mb_load_size, 0, mb_kernel_size - mb_load_size);
fclose(f);
}
mbs.mb_buf_phys = mh_load_addr;
mbs.mb_buf_size = TARGET_PAGE_ALIGN(mb_kernel_size);
mbs.offset_mbinfo = mbs.mb_buf_size;
/* Calculate space for cmdlines, bootloader name, and mb_mods */
cmdline_len = strlen(kernel_filename) + 1;
cmdline_len += strlen(kernel_cmdline) + 1;
if (initrd_filename) {
const char *r = initrd_filename;
cmdline_len += strlen(r) + 1;
mbs.mb_mods_avail = 1;
while (*(r = get_opt_value(NULL, 0, r))) {
mbs.mb_mods_avail++;
r++;
}
}
mbs.mb_buf_size += cmdline_len;
mbs.mb_buf_size += MB_MOD_SIZE * mbs.mb_mods_avail;
mbs.mb_buf_size += strlen(bootloader_name) + 1;
mbs.mb_buf_size = TARGET_PAGE_ALIGN(mbs.mb_buf_size);
/* enlarge mb_buf to hold cmdlines, bootloader, mb-info structs */
mbs.mb_buf = g_realloc(mbs.mb_buf, mbs.mb_buf_size);
mbs.offset_cmdlines = mbs.offset_mbinfo + mbs.mb_mods_avail * MB_MOD_SIZE;
mbs.offset_bootloader = mbs.offset_cmdlines + cmdline_len;
if (initrd_filename) {
const char *next_initrd;
char not_last, tmpbuf[strlen(initrd_filename) + 1];
mbs.offset_mods = mbs.mb_buf_size;
do {
char *next_space;
int mb_mod_length;
uint32_t offs = mbs.mb_buf_size;
next_initrd = get_opt_value(tmpbuf, sizeof(tmpbuf), initrd_filename);
not_last = *next_initrd;
/* if a space comes after the module filename, treat everything
after that as parameters */
hwaddr c = mb_add_cmdline(&mbs, tmpbuf);
if ((next_space = strchr(tmpbuf, ' ')))
*next_space = '\0';
mb_debug("multiboot loading module: %s\n", tmpbuf);
mb_mod_length = get_image_size(tmpbuf);
if (mb_mod_length < 0) {
fprintf(stderr, "Failed to open file '%s'\n", tmpbuf);
exit(1);
}
mbs.mb_buf_size = TARGET_PAGE_ALIGN(mb_mod_length + mbs.mb_buf_size);
mbs.mb_buf = g_realloc(mbs.mb_buf, mbs.mb_buf_size);
load_image(tmpbuf, (unsigned char *)mbs.mb_buf + offs);
mb_add_mod(&mbs, mbs.mb_buf_phys + offs,
mbs.mb_buf_phys + offs + mb_mod_length, c);
mb_debug("mod_start: %p\nmod_end: %p\n cmdline: "TARGET_FMT_plx"\n",
(char *)mbs.mb_buf + offs,
(char *)mbs.mb_buf + offs + mb_mod_length, c);
initrd_filename = next_initrd+1;
} while (not_last);
}
/* Commandline support */
char kcmdline[strlen(kernel_filename) + strlen(kernel_cmdline) + 2];
snprintf(kcmdline, sizeof(kcmdline), "%s %s",
kernel_filename, kernel_cmdline);
stl_p(bootinfo + MBI_CMDLINE, mb_add_cmdline(&mbs, kcmdline));
stl_p(bootinfo + MBI_BOOTLOADER, mb_add_bootloader(&mbs, bootloader_name));
stl_p(bootinfo + MBI_MODS_ADDR, mbs.mb_buf_phys + mbs.offset_mbinfo);
stl_p(bootinfo + MBI_MODS_COUNT, mbs.mb_mods_count); /* mods_count */
/* the kernel is where we want it to be now */
stl_p(bootinfo + MBI_FLAGS, MULTIBOOT_FLAGS_MEMORY
| MULTIBOOT_FLAGS_BOOT_DEVICE
| MULTIBOOT_FLAGS_CMDLINE
| MULTIBOOT_FLAGS_MODULES
| MULTIBOOT_FLAGS_MMAP
| MULTIBOOT_FLAGS_BOOTLOADER);
stl_p(bootinfo + MBI_BOOT_DEVICE, 0x8000ffff); /* XXX: use the -boot switch? */
stl_p(bootinfo + MBI_MMAP_ADDR, ADDR_E820_MAP);
mb_debug("multiboot: mh_entry_addr = %#x\n", mh_entry_addr);
mb_debug(" mb_buf_phys = "TARGET_FMT_plx"\n", mbs.mb_buf_phys);
mb_debug(" mod_start = "TARGET_FMT_plx"\n", mbs.mb_buf_phys + mbs.offset_mods);
mb_debug(" mb_mods_count = %d\n", mbs.mb_mods_count);
/* save bootinfo off the stack */
mb_bootinfo_data = g_memdup(bootinfo, sizeof(bootinfo));
/* Pass variables to option rom */
fw_cfg_add_i32(fw_cfg, FW_CFG_KERNEL_ENTRY, mh_entry_addr);
fw_cfg_add_i32(fw_cfg, FW_CFG_KERNEL_ADDR, mh_load_addr);
fw_cfg_add_i32(fw_cfg, FW_CFG_KERNEL_SIZE, mbs.mb_buf_size);
fw_cfg_add_bytes(fw_cfg, FW_CFG_KERNEL_DATA,
mbs.mb_buf, mbs.mb_buf_size);
fw_cfg_add_i32(fw_cfg, FW_CFG_INITRD_ADDR, ADDR_MBI);
fw_cfg_add_i32(fw_cfg, FW_CFG_INITRD_SIZE, sizeof(bootinfo));
fw_cfg_add_bytes(fw_cfg, FW_CFG_INITRD_DATA, mb_bootinfo_data,
sizeof(bootinfo));
option_rom[nb_option_roms].name = "multiboot.bin";
option_rom[nb_option_roms].bootindex = 0;
nb_option_roms++;
return 1; /* yes, we are multiboot */
}
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