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Linux kernel mirror (for testing) git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
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#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);}