OwlCyberSecurity - MANAGER

Edit File: insert-sys-cert.c

/* Write the contents of the <certfile> into kernel symbol system_extra_cert
 *
 * Copyright (C) IBM Corporation, 2015
 *
 * Author: Mehmet Kayaalp <mkayaalp@linux.vnet.ibm.com>
 *
 * This software may be used and distributed according to the terms
 * of the GNU General Public License, incorporated herein by reference.
 *
 * Usage: insert-sys-cert [-s <System.map>] -b <vmlinux> -c <certfile>
 *                        [-s <System.map>] -z <bzImage> -c <certfile>
 */

#define _GNU_SOURCE
#include <stdio.h>
#include <ctype.h>
#include <string.h>
#include <limits.h>
#include <stdbool.h>
#include <errno.h>
#include <stdlib.h>
#include <stdarg.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/mman.h>
#include <fcntl.h>
#include <unistd.h>
#include <elf.h>

#define CERT_SYM  "system_extra_cert"
#define USED_SYM  "system_extra_cert_used"
#define LSIZE_SYM "system_certificate_list_size"

#define info(format, args...) fprintf(stderr, "INFO:    " format, ## args)
#define warn(format, args...) fprintf(stdout, "WARNING: " format, ## args)
#define  err(format, args...) fprintf(stderr, "ERROR:   " format, ## args)

#if UINTPTR_MAX == 0xffffffff
#define CURRENT_ELFCLASS ELFCLASS32
#define Elf_Ehdr	Elf32_Ehdr
#define Elf_Shdr	Elf32_Shdr
#define Elf_Sym		Elf32_Sym
#else
#define CURRENT_ELFCLASS ELFCLASS64
#define Elf_Ehdr	Elf64_Ehdr
#define Elf_Shdr	Elf64_Shdr
#define Elf_Sym		Elf64_Sym
#endif

static unsigned char endianness(void)
{
	uint16_t two_byte = 0x00FF;
	uint8_t low_address = *((uint8_t *)&two_byte);

if (low_address == 0)
		return ELFDATA2MSB;
	else
		return ELFDATA2LSB;
}

struct sym {
	char *name;
	unsigned long address;
	unsigned long offset;
	void *content;
	int size;
};

static unsigned long get_offset_from_address(Elf_Ehdr *hdr, unsigned long addr)
{
	Elf_Shdr *x;
	unsigned int i, num_sections;

x = (void *)hdr + hdr->e_shoff;
	if (hdr->e_shnum == SHN_UNDEF)
		num_sections = x[0].sh_size;
	else
		num_sections = hdr->e_shnum;

for (i = 1; i < num_sections; i++) {
		unsigned long start = x[i].sh_addr;
		unsigned long end = start + x[i].sh_size;
		unsigned long offset = x[i].sh_offset;

if (addr >= start && addr <= end)
			return addr - start + offset;
	}
	return 0;
}

#define LINE_SIZE 100

static void get_symbol_from_map(Elf_Ehdr *hdr, FILE *f, char *name,
				struct sym *s)
{
	char l[LINE_SIZE];
	char *w, *p, *n;

s->size = 0;
	s->address = 0;
	s->offset = 0;
	if (fseek(f, 0, SEEK_SET) != 0) {
		perror("File seek failed");
		exit(EXIT_FAILURE);
	}
	while (fgets(l, LINE_SIZE, f)) {
		p = strchr(l, '\n');
		if (!p) {
			err("Missing line ending.\n");
			return;
		}
		n = strstr(l, name);
		if (n)
			break;
	}
	if (!n) {
		err("Unable to find symbol: %s\n", name);
		return;
	}
	w = strchr(l, ' ');
	if (!w)
		return;

*w = '\0';
	s->address = strtoul(l, NULL, 16);
	if (s->address == 0)
		return;
	s->offset = get_offset_from_address(hdr, s->address);
	s->name = name;
	s->content = (void *)hdr + s->offset;
}

static Elf_Sym *find_elf_symbol(Elf_Ehdr *hdr, Elf_Shdr *symtab, char *name)
{
	Elf_Sym *sym, *symtab_start;
	char *strtab, *symname;
	unsigned int link;
	Elf_Shdr *x;
	int i, n;

x = (void *)hdr + hdr->e_shoff;
	link = symtab->sh_link;
	symtab_start = (void *)hdr + symtab->sh_offset;
	n = symtab->sh_size / symtab->sh_entsize;
	strtab = (void *)hdr + x[link].sh_offset;

for (i = 0; i < n; i++) {
		sym = &symtab_start[i];
		symname = strtab + sym->st_name;
		if (strcmp(symname, name) == 0)
			return sym;
	}
	err("Unable to find symbol: %s\n", name);
	return NULL;
}

static void get_symbol_from_table(Elf_Ehdr *hdr, Elf_Shdr *symtab,
				  char *name, struct sym *s)
{
	Elf_Shdr *sec;
	int secndx;
	Elf_Sym *elf_sym;
	Elf_Shdr *x;

x = (void *)hdr + hdr->e_shoff;
	s->size = 0;
	s->address = 0;
	s->offset = 0;
	elf_sym = find_elf_symbol(hdr, symtab, name);
	if (!elf_sym)
		return;
	secndx = elf_sym->st_shndx;
	if (!secndx)
		return;
	sec = &x[secndx];
	s->size = elf_sym->st_size;
	s->address = elf_sym->st_value;
	s->offset = s->address - sec->sh_addr
			       + sec->sh_offset;
	s->name = name;
	s->content = (void *)hdr + s->offset;
}

static Elf_Shdr *get_symbol_table(Elf_Ehdr *hdr)
{
	Elf_Shdr *x;
	unsigned int i, num_sections;

x = (void *)hdr + hdr->e_shoff;
	if (hdr->e_shnum == SHN_UNDEF)
		num_sections = x[0].sh_size;
	else
		num_sections = hdr->e_shnum;

for (i = 1; i < num_sections; i++)
		if (x[i].sh_type == SHT_SYMTAB)
			return &x[i];
	return NULL;
}

static void *map_file(char *file_name, int *size)
{
	struct stat st;
	void *map;
	int fd;

fd = open(file_name, O_RDWR);
	if (fd < 0) {
		perror(file_name);
		return NULL;
	}
	if (fstat(fd, &st)) {
		perror("Could not determine file size");
		close(fd);
		return NULL;
	}
	*size = st.st_size;
	map = mmap(NULL, *size, PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0);
	if (map == MAP_FAILED) {
		perror("Mapping to memory failed");
		close(fd);
		return NULL;
	}
	close(fd);
	return map;
}

static char *read_file(char *file_name, int *size)
{
	struct stat st;
	char *buf;
	int fd;

fd = open(file_name, O_RDONLY);
	if (fd < 0) {
		perror(file_name);
		return NULL;
	}
	if (fstat(fd, &st)) {
		perror("Could not determine file size");
		close(fd);
		return NULL;
	}
	*size = st.st_size;
	buf = malloc(*size);
	if (!buf) {
		perror("Allocating memory failed");
		close(fd);
		return NULL;
	}
	if (read(fd, buf, *size) != *size) {
		perror("File read failed");
		close(fd);
		return NULL;
	}
	close(fd);
	return buf;
}

static void get_payload_info(char *bzimage, int *offset, int *size)
{
	unsigned int system_offset;
	unsigned char setup_sectors;

setup_sectors = bzimage[0x1f1] + 1;
	system_offset = setup_sectors * 512;
	*offset = system_offset + *((int*)&bzimage[0x248]);
	*size = *((int*)&bzimage[0x24c]);
}

static void update_payload_info(char* bzimage, int new_size)
{
	int offset, size;
	get_payload_info(bzimage, &offset, &size);
	*((int*)&bzimage[0x24c]) = new_size;
	if (new_size < size)
		memset(bzimage + offset + new_size, 0, size - new_size);
}

struct zipper {
	unsigned char pattern[10];
	int length;
	char *command;
	char *compress;
};

struct zipper zippers[] = {
	{{0x7F,'E','L','F'}, 4, "cat", "cat"},
	{{0x1F,0x8B}, 2, "gunzip", "gzip -n -f -9"},
	{{0xFD,'7','z','X','Z',0}, 6, "unxz", "xz"},
	{{'B','Z','h'},3, "bunzip2", "bzip2 -9"},
	{{0xFF,'L','Z','M','A',0}, 6, "unlzma", "lzma -9"},
	{{0xD3,'L','Z','O',0,'\r','\n',0x20,'\n'}, 9, "lzop -d", "lzop -9"}
};

static struct zipper* get_zipper(char *p) {
	int i;
	for (i = 0; i < sizeof(zippers)/sizeof(struct zipper); i++) {
		if (memcmp(p, zippers[i].pattern, zippers[i].length) == 0)
			return &zippers[i];
	}
	return NULL;
}

/*
 * This only works for x86 bzImage
 */
static void extract_vmlinux(char *bzimage, int bzimage_size,
			char **file, struct zipper **zipper)
{
	int r;
	char src[15] = "vmlinux-XXXXXX";
	char dest[15] = "vmlinux-XXXXXX";
	char cmd[100];
	int src_fd, dest_fd;
	int offset, size;
	struct zipper *z;

/* TODO: verify that bzImage is supported */

get_payload_info(bzimage, &offset, &size);
	z = get_zipper(bzimage + offset);
	if (z == NULL) {
		err("Unable to determine the compression of vmlinux\n");
		return;
	}

src_fd = mkstemp(src);
	if (src_fd == -1) {
		perror("Could not create temp file");
		return;
	}

r = write(src_fd, bzimage + offset, size);
	if (r != size) {
		perror("Could not write vmlinux");
		return;
	}
	dest_fd = mkstemp(dest);
	if (dest_fd == -1) {
		perror("Could not create temp file");
		return;
	}

snprintf(cmd, sizeof(cmd), "%s <%s >%s", z->command, src, dest);
	info("Executing: %s\n", cmd);
	r = system(cmd);
	if (r!=0)
		warn("Possible errors when extracting\n");

r = remove(src);
	if (r!=0)
		perror(src);

*file = strdup(dest);
	*zipper = z;
}

static void repack_image(char *bzimage, int bzimage_size,
			char* vmlinux_file, struct zipper *z)
{
	char tmp[15] = "vmlinux-XXXXXX";
	char cmd[100];
	int fd;
	struct stat st;
	int new_size;
	int r;
	int offset, size;

get_payload_info(bzimage, &offset, &size);

fd = mkstemp(tmp);
	if (fd == -1) {
		perror("Could not create temp file");
		return;
	}
	snprintf(cmd, sizeof(cmd), "%s <%s >%s",
			z->compress, vmlinux_file, tmp);

info("Executing: %s\n", cmd);
	r = system(cmd);
	if (r!=0)
		warn("Possible errors when compressing\n");

r = remove(vmlinux_file);
	if (r!=0)
		perror(vmlinux_file);

if (fstat(fd, &st)) {
		perror("Could not determine file size");
		close(fd);

}
	new_size = st.st_size;
	if (new_size > size) {
		err("Increase in compressed size is not supported.\n");
		err("Old size was %d, new size is %d\n", size, new_size);
		exit(EXIT_FAILURE);
	}

r = read(fd, bzimage + offset, new_size);
	if (r != new_size)
		perror(tmp);

r = remove(tmp);
	if (r!=0)
		perror(tmp);

/* x86 specific patching of bzimage */
	update_payload_info(bzimage, new_size);

/* TODO: update CRC */

}

static void fill_random(unsigned char *p, int n) {
	srand(0);
	int i;
	for (i = 0; i < n; i++)
		p[i] = rand();
}

static void print_sym(Elf_Ehdr *hdr, struct sym *s)
{
	info("sym:    %s\n", s->name);
	info("addr:   0x%lx\n", s->address);
	info("size:   %d\n", s->size);
	info("offset: 0x%lx\n", (unsigned long)s->offset);
}

static void print_usage(char *e)
{
	printf("Usage: %s [-s <System.map>] -b <vmlinux> -c <certfile>\n", e);
	printf("       %s [-s <System.map>] -z <bzImage> -c <certfile>\n", e);
}

int main(int argc, char **argv)
{
	char *system_map_file = NULL;
	char *vmlinux_file = NULL;
	char *bzimage_file = NULL;
	char *cert_file = NULL;
	int vmlinux_size;
	int bzimage_size;
	int cert_size;
	Elf_Ehdr *hdr;
	char *cert;
	char *bzimage = NULL;
	struct zipper *z = NULL;
	FILE *system_map;
	unsigned long *lsize;
	int *used;
	int opt;
	Elf_Shdr *symtab = NULL;
	struct sym cert_sym, lsize_sym, used_sym;

while ((opt = getopt(argc, argv, "b:z:c:s:")) != -1) {
		switch (opt) {
		case 's':
			system_map_file = optarg;
			break;
		case 'b':
			vmlinux_file = optarg;
			break;
		case 'z':
			bzimage_file = optarg;
			break;
		case 'c':
			cert_file = optarg;
			break;
		default:
			break;
		}
	}

if (!cert_file ||
	(!vmlinux_file && !bzimage_file) ||
	(vmlinux_file && bzimage_file)) {
		print_usage(argv[0]);
		exit(EXIT_FAILURE);
	}

cert = read_file(cert_file, &cert_size);
	if (!cert)
		exit(EXIT_FAILURE);

if (bzimage_file) {
		bzimage = map_file(bzimage_file, &bzimage_size);
		if (!bzimage)
			exit(EXIT_FAILURE);

extract_vmlinux(bzimage, bzimage_size, &vmlinux_file, &z);
		if (!vmlinux_file)
			exit(EXIT_FAILURE);
	}

hdr = map_file(vmlinux_file, &vmlinux_size);
	if (!hdr)
		exit(EXIT_FAILURE);

if (vmlinux_size < sizeof(*hdr)) {
		err("Invalid ELF file.\n");
		exit(EXIT_FAILURE);
	}

if ((hdr->e_ident[EI_MAG0] != ELFMAG0) ||
	    (hdr->e_ident[EI_MAG1] != ELFMAG1) ||
	    (hdr->e_ident[EI_MAG2] != ELFMAG2) ||
	    (hdr->e_ident[EI_MAG3] != ELFMAG3)) {
		err("Invalid ELF magic.\n");
		exit(EXIT_FAILURE);
	}

if (hdr->e_ident[EI_CLASS] != CURRENT_ELFCLASS) {
		err("ELF class mismatch.\n");
		exit(EXIT_FAILURE);
	}

if (hdr->e_ident[EI_DATA] != endianness()) {
		err("ELF endian mismatch.\n");
		exit(EXIT_FAILURE);
	}

if (hdr->e_shoff > vmlinux_size) {
		err("Could not find section header.\n");
		exit(EXIT_FAILURE);
	}

symtab = get_symbol_table(hdr);
	if (!symtab) {
		warn("Could not find the symbol table.\n");
		if (!system_map_file) {
			err("Please provide a System.map file.\n");
			print_usage(argv[0]);
			exit(EXIT_FAILURE);
		}

system_map = fopen(system_map_file, "r");
		if (!system_map) {
			perror(system_map_file);
			exit(EXIT_FAILURE);
		}
		get_symbol_from_map(hdr, system_map, CERT_SYM, &cert_sym);
		get_symbol_from_map(hdr, system_map, USED_SYM, &used_sym);
		get_symbol_from_map(hdr, system_map, LSIZE_SYM, &lsize_sym);
		cert_sym.size = used_sym.address - cert_sym.address;
	} else {
		info("Symbol table found.\n");
		if (system_map_file)
			warn("System.map is ignored.\n");
		get_symbol_from_table(hdr, symtab, CERT_SYM, &cert_sym);
		get_symbol_from_table(hdr, symtab, USED_SYM, &used_sym);
		get_symbol_from_table(hdr, symtab, LSIZE_SYM, &lsize_sym);
	}

if (!cert_sym.offset || !lsize_sym.offset || !used_sym.offset)
		exit(EXIT_FAILURE);

print_sym(hdr, &cert_sym);
	print_sym(hdr, &used_sym);
	print_sym(hdr, &lsize_sym);

lsize = (unsigned long *)lsize_sym.content;
	used = (int *)used_sym.content;

if (cert_sym.size < cert_size) {
		err("Certificate is larger than the reserved area!\n");
		exit(EXIT_FAILURE);
	}

/* If the existing cert is the same, don't overwrite */
	if (cert_size > 0 && cert_size == *used &&
	    strncmp(cert_sym.content, cert, cert_size) == 0) {
		warn("Certificate was already inserted.\n");
		exit(EXIT_SUCCESS);
	}

if (*used > 0)
		warn("Replacing previously inserted certificate.\n");

memcpy(cert_sym.content, cert, cert_size);

if (cert_size < cert_sym.size)
		/* This makes the reserved space incompressable */
		fill_random(cert_sym.content + cert_size,
				cert_sym.size - cert_size);

*lsize = *lsize + cert_size - *used;
	*used = cert_size;
	info("Inserted the contents of %s into %lx.\n", cert_file,
						cert_sym.address);
	info("Used %d bytes out of %d bytes reserved.\n", *used,
						 cert_sym.size);

if (munmap(hdr, vmlinux_size) == -1) {
		perror(vmlinux_file);
		exit(EXIT_FAILURE);
	}

if (bzimage) {
		repack_image(bzimage, bzimage_size, vmlinux_file, z);
	}

exit(EXIT_SUCCESS);
}