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KEYS: Reserve an extra certificate symbol for inserting without recompiling 

Place a system_extra_cert buffer of configurable size, right after the
system_certificate_list, so that inserted keys can be readily processed by
the existing mechanism. Added script takes a key file and a kernel image
and inserts its contents to the reserved area. The
system_certificate_list_size is also adjusted accordingly.

Call the script as:

    scripts/insert-sys-cert -b <vmlinux> -c <certfile>

If vmlinux has no symbol table, supply System.map file with -s flag.
Subsequent runs replace the previously inserted key, instead of appending
the new one.

Signed-off-by: Mehmet Kayaalp <mkayaalp@linux.vnet.ibm.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: Mimi Zohar <zohar@linux.vnet.ibm.com>
hifive-unleashed-5.1
Mehmet Kayaalp 2015-11-24 16:18:05 -05:00 committed by David Howells
parent 5d06ee20b6
commit c4c3610595
5 changed files with 440 additions and 0 deletions
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16
certs/Kconfig
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@ -39,4 +39,20 @@ config SYSTEM_TRUSTED_KEYS
form of DER-encoded *.x509 files in the top-level build directory, form of DER-encoded *.x509 files in the top-level build directory,
those are no longer used. You will need to set this option instead. those are no longer used. You will need to set this option instead.
config SYSTEM_EXTRA_CERTIFICATE
bool "Reserve area for inserting a certificate without recompiling"
depends on SYSTEM_TRUSTED_KEYRING
help
If set, space for an extra certificate will be reserved in the kernel
image. This allows introducing a trusted certificate to the default
system keyring without recompiling the kernel.
config SYSTEM_EXTRA_CERTIFICATE_SIZE
int "Number of bytes to reserve for the extra certificate"
depends on SYSTEM_EXTRA_CERTIFICATE
default 4096
help
This is the number of bytes reserved in the kernel image for a
certificate to be inserted.
endmenu endmenu

12
certs/system_certificates.S
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@ -13,6 +13,18 @@ __cert_list_start:
.incbin "certs/x509_certificate_list" .incbin "certs/x509_certificate_list"
__cert_list_end: __cert_list_end:
#ifdef CONFIG_SYSTEM_EXTRA_CERTIFICATE
.globl VMLINUX_SYMBOL(system_extra_cert)
.size system_extra_cert, CONFIG_SYSTEM_EXTRA_CERTIFICATE_SIZE
VMLINUX_SYMBOL(system_extra_cert):
.fill CONFIG_SYSTEM_EXTRA_CERTIFICATE_SIZE, 1, 0
.globl VMLINUX_SYMBOL(system_extra_cert_used)
VMLINUX_SYMBOL(system_extra_cert_used):
.int 0
#endif /* CONFIG_SYSTEM_EXTRA_CERTIFICATE */
.align 8 .align 8
.globl VMLINUX_SYMBOL(system_certificate_list_size) .globl VMLINUX_SYMBOL(system_certificate_list_size)
VMLINUX_SYMBOL(system_certificate_list_size): VMLINUX_SYMBOL(system_certificate_list_size):

1
scripts/.gitignore vendored
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@ -13,3 +13,4 @@ sortextable
asn1_compiler asn1_compiler
extract-cert extract-cert
sign-file sign-file
insert-sys-cert

1
scripts/Makefile
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@ -19,6 +19,7 @@ hostprogs-$(CONFIG_BUILDTIME_EXTABLE_SORT) += sortextable
hostprogs-$(CONFIG_ASN1) += asn1_compiler hostprogs-$(CONFIG_ASN1) += asn1_compiler
hostprogs-$(CONFIG_MODULE_SIG) += sign-file hostprogs-$(CONFIG_MODULE_SIG) += sign-file
hostprogs-$(CONFIG_SYSTEM_TRUSTED_KEYRING) += extract-cert hostprogs-$(CONFIG_SYSTEM_TRUSTED_KEYRING) += extract-cert
hostprogs-$(CONFIG_SYSTEM_EXTRA_CERTIFICATE) += insert-sys-cert
HOSTCFLAGS_sortextable.o = -I$(srctree)/tools/include HOSTCFLAGS_sortextable.o = -I$(srctree)/tools/include
HOSTCFLAGS_asn1_compiler.o = -I$(srctree)/include HOSTCFLAGS_asn1_compiler.o = -I$(srctree)/include

410
scripts/insert-sys-cert.c 100644
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@ -0,0 +1,410 @@
/* 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>
*/
#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 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);
}
int main(int argc, char **argv)
{
char *system_map_file = NULL;
char *vmlinux_file = NULL;
char *cert_file = NULL;
int vmlinux_size;
int cert_size;
Elf_Ehdr *hdr;
char *cert;
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:c:s:")) != -1) {
switch (opt) {
case 's':
system_map_file = optarg;
break;
case 'b':
vmlinux_file = optarg;
break;
case 'c':
cert_file = optarg;
break;
default:
break;
}
}
if (!vmlinux_file || !cert_file) {
print_usage(argv[0]);
exit(EXIT_FAILURE);
}
cert = read_file(cert_file, &cert_size);
if (!cert)
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 == *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)
memset(cert_sym.content + cert_size,
0, 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);
exit(EXIT_SUCCESS);
}