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>

5 files changed, 440 insertions, 0 deletions

diff --git a/certs/Kconfig b/certs/Kconfig
index b030b9c7ed34..f0f8a4433685 100644
--- a/certs/Kconfig
+++ b/certs/Kconfig
@@ -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
diff --git a/certs/system_certificates.S b/certs/system_certificates.S
index 9216e8c81764..f82e1b22eac4 100644
--- a/certs/system_certificates.S
+++ b/certs/system_certificates.S
@@ -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):
diff --git a/scripts/.gitignore b/scripts/.gitignore
index 1f78169d4254..e063daa3ec4a 100644
--- a/scripts/.gitignore
+++ b/scripts/.gitignore
@@ -13,3 +13,4 @@ sortextable
 asn1_compiler
 extract-cert
 sign-file
+insert-sys-cert
diff --git a/scripts/Makefile b/scripts/Makefile
index fd0d53d4a234..822ab4a6a4aa 100644
--- a/scripts/Makefile
+++ b/scripts/Makefile
@@ -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
index 000000000000..8902836c2342
--- /dev/null
+++ b/scripts/insert-sys-cert.c
@@ -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);
+}