KEYS: Reserve an extra certificate symbol for inserting without recompiling
authorMehmet Kayaalp <mkayaalp@linux.vnet.ibm.com>
Tue, 24 Nov 2015 21:18:05 +0000 (16:18 -0500)
committerDavid Howells <dhowells@redhat.com>
Fri, 26 Feb 2016 15:30:20 +0000 (15:30 +0000)
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>
certs/Kconfig
certs/system_certificates.S
scripts/.gitignore
scripts/Makefile
scripts/insert-sys-cert.c [new file with mode: 0644]

index b030b9c7ed34ad05f62faf8f253cfb0efd1c01b4..f0f8a4433685aaa0c42ac776c590e9840e1ba52d 100644 (file)
@@ -39,4 +39,20 @@ config SYSTEM_TRUSTED_KEYS
          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.
 
+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
index 9216e8c817649eefd3a6d9c2a64a1b4da2b38ffe..f82e1b22eac43b3e8a13b5e25d741f00803a208a 100644 (file)
@@ -13,6 +13,18 @@ __cert_list_start:
        .incbin "certs/x509_certificate_list"
 __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
        .globl VMLINUX_SYMBOL(system_certificate_list_size)
 VMLINUX_SYMBOL(system_certificate_list_size):
index 1f78169d425493356b560459ec5ef2da1b93c903..e063daa3ec4a3d8b22556b1cbc9f6facfee75550 100644 (file)
@@ -13,3 +13,4 @@ sortextable
 asn1_compiler
 extract-cert
 sign-file
+insert-sys-cert
index fd0d53d4a2346f762aa52f86c7b66abd78ae7470..822ab4a6a4aa34b513f6c55f1dd2ab27ef69fe43 100644 (file)
@@ -19,6 +19,7 @@ hostprogs-$(CONFIG_BUILDTIME_EXTABLE_SORT) += sortextable
 hostprogs-$(CONFIG_ASN1)        += asn1_compiler
 hostprogs-$(CONFIG_MODULE_SIG)  += sign-file
 hostprogs-$(CONFIG_SYSTEM_TRUSTED_KEYRING) += extract-cert
+hostprogs-$(CONFIG_SYSTEM_EXTRA_CERTIFICATE) += insert-sys-cert
 
 HOSTCFLAGS_sortextable.o = -I$(srctree)/tools/include
 HOSTCFLAGS_asn1_compiler.o = -I$(srctree)/include
diff --git a/scripts/insert-sys-cert.c b/scripts/insert-sys-cert.c
new file mode 100644 (file)
index 0000000..8902836
--- /dev/null
@@ -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);
+}