diff options
Diffstat (limited to 'crypto/fips140_gen_hmac.c')
| -rw-r--r-- | crypto/fips140_gen_hmac.c | 194 |
1 files changed, 194 insertions, 0 deletions
diff --git a/crypto/fips140_gen_hmac.c b/crypto/fips140_gen_hmac.c new file mode 100644 index 000000000..69f754d38 --- /dev/null +++ b/crypto/fips140_gen_hmac.c @@ -0,0 +1,194 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* + * Copyright (C) 2021 - Google LLC + * Author: Ard Biesheuvel <ardb@google.com> + * + * This is a host tool that is intended to be used to take the HMAC digest of + * the .text and .rodata sections of the fips140.ko module, and store it inside + * the module. The module will perform an integrity selfcheck at module_init() + * time, by recalculating the digest and comparing it with the value calculated + * here. + * + * Note that the peculiar way an HMAC is being used as a digest with a public + * key rather than as a symmetric key signature is mandated by FIPS 140-2. + */ + +#include <elf.h> +#include <fcntl.h> +#include <stdio.h> +#include <stdlib.h> +#include <string.h> +#include <sys/mman.h> +#include <sys/stat.h> +#include <sys/types.h> +#include <unistd.h> + +#include <openssl/hmac.h> + +static Elf64_Ehdr *ehdr; +static Elf64_Shdr *shdr; +static int num_shdr; +static const char *strtab, *shstrtab; +static Elf64_Sym *syms; +static int num_syms; + +static Elf64_Shdr *find_symtab_section(void) +{ + int i; + + for (i = 0; i < num_shdr; i++) + if (shdr[i].sh_type == SHT_SYMTAB) + return &shdr[i]; + return NULL; +} + +static int get_section_idx(const char *name) +{ + int i; + + for (i = 0; i < num_shdr; i++) + if (!strcmp(shstrtab + shdr[i].sh_name, name)) + return i; + return -1; +} + +static int get_sym_idx(const char *sym_name) +{ + int i; + + for (i = 0; i < num_syms; i++) + if (!strcmp(strtab + syms[i].st_name, sym_name)) + return i; + return -1; +} + +static void *get_sym_addr(const char *sym_name) +{ + int i = get_sym_idx(sym_name); + + if (i >= 0) + return (void *)ehdr + shdr[syms[i].st_shndx].sh_offset + + syms[i].st_value; + return NULL; +} + +static int update_rela_ref(const char *name) +{ + /* + * We need to do a couple of things to ensure that the copied RELA data + * is accessible to the module itself at module init time: + * - the associated entry in the symbol table needs to refer to the + * correct section index, and have SECTION type and GLOBAL linkage. + * - the 'count' global variable in the module need to be set to the + * right value based on the size of the RELA section. + */ + unsigned int *size_var; + int sec_idx, sym_idx; + char str[32]; + + sprintf(str, "fips140_rela_%s", name); + size_var = get_sym_addr(str); + if (!size_var) { + printf("variable '%s' not found, disregarding .%s section\n", + str, name); + return 1; + } + + sprintf(str, "__sec_rela_%s", name); + sym_idx = get_sym_idx(str); + + sprintf(str, ".init.rela.%s", name); + sec_idx = get_section_idx(str); + + if (sec_idx < 0 || sym_idx < 0) { + fprintf(stderr, "failed to locate metadata for .%s section in binary\n", + name); + return 0; + } + + syms[sym_idx].st_shndx = sec_idx; + syms[sym_idx].st_info = (STB_GLOBAL << 4) | STT_SECTION; + + size_var[1] = shdr[sec_idx].sh_size / sizeof(Elf64_Rela); + + return 1; +} + +static void hmac_section(HMAC_CTX *hmac, const char *start, const char *end) +{ + void *start_addr = get_sym_addr(start); + void *end_addr = get_sym_addr(end); + + HMAC_Update(hmac, start_addr, end_addr - start_addr); +} + +int main(int argc, char **argv) +{ + Elf64_Shdr *symtab_shdr; + const char *hmac_key; + unsigned char *dg; + unsigned int dglen; + struct stat stat; + HMAC_CTX *hmac; + int fd, ret; + + if (argc < 2) { + fprintf(stderr, "file argument missing\n"); + exit(EXIT_FAILURE); + } + + fd = open(argv[1], O_RDWR); + if (fd < 0) { + fprintf(stderr, "failed to open %s\n", argv[1]); + exit(EXIT_FAILURE); + } + + ret = fstat(fd, &stat); + if (ret < 0) { + fprintf(stderr, "failed to stat() %s\n", argv[1]); + exit(EXIT_FAILURE); + } + + ehdr = mmap(0, stat.st_size, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0); + if (ehdr == MAP_FAILED) { + fprintf(stderr, "failed to mmap() %s\n", argv[1]); + exit(EXIT_FAILURE); + } + + shdr = (void *)ehdr + ehdr->e_shoff; + num_shdr = ehdr->e_shnum; + + symtab_shdr = find_symtab_section(); + + syms = (void *)ehdr + symtab_shdr->sh_offset; + num_syms = symtab_shdr->sh_size / sizeof(Elf64_Sym); + + strtab = (void *)ehdr + shdr[symtab_shdr->sh_link].sh_offset; + shstrtab = (void *)ehdr + shdr[ehdr->e_shstrndx].sh_offset; + + if (!update_rela_ref("text") || !update_rela_ref("rodata")) + exit(EXIT_FAILURE); + + hmac_key = get_sym_addr("fips140_integ_hmac_key"); + if (!hmac_key) { + fprintf(stderr, "failed to locate HMAC key in binary\n"); + exit(EXIT_FAILURE); + } + + dg = get_sym_addr("fips140_integ_hmac_digest"); + if (!dg) { + fprintf(stderr, "failed to locate HMAC digest in binary\n"); + exit(EXIT_FAILURE); + } + + hmac = HMAC_CTX_new(); + HMAC_Init_ex(hmac, hmac_key, strlen(hmac_key), EVP_sha256(), NULL); + + hmac_section(hmac, "__fips140_text_start", "__fips140_text_end"); + hmac_section(hmac, "__fips140_rodata_start", "__fips140_rodata_end"); + + HMAC_Final(hmac, dg, &dglen); + + close(fd); + return 0; +} |