[PATCH v3 01/19] Add suport for signing grub with an appended signature

[Daniel Axtens]

From: Rashmica Gupta <rashmica.g@gmail.com>

Add infrastructure to allow firmware to verify the integrity of grub
by use of a Linux-kernel-module-style appended signature. We initially
target powerpc-ieee1275, but the code should be extensible to other
platforms.

Usually these signatures are appended to a file without modifying the
ELF file itself. (This is what the 'sign-file' tool does, for example.)
The verifier loads the signed file from the file system and looks at the
end of the file for the appended signature. However, on powerpc-ieee1275
platforms, the bootloader is often stored directly in the PReP partition
as raw bytes without a file-system. This makes determining the location
of an appended signature more difficult.

To address this, we add a new ELF note.

The name field of shall be the string "Appended-Signature", zero-padded
to 4 byte alignment. The type field shall be 0x41536967 (the ASCII values
for the string "ASig"). It must be the final section in the ELF binary.

The description shall contain the appended signature structure as defined
by the Linux kernel. The description will also be padded to be a multiple
of 4 bytes. The padding shall be added before the appended signature
structure (not at the end) so that the final bytes of a signed ELF file
are the appended signature magic.

A subsequent patch documents how to create a grub core.img validly signed
under this scheme.

Signed-off-by: Daniel Axtens <dja@axtens.net>
Signed-off-by: Rashmica Gupta <rashmica.g@gmail.com>

---

You can experiment with this code with a patched version of SLOF
that verifies these signatures. You can find one at:
   https://github.com/daxtens/SLOF

I will be proposing this for inclusion in a future Power Architecture
Platform Reference (PAPR).

v3: Fix a nit, thanks Stefan.
---
 include/grub/util/install.h |  8 ++++++--
 include/grub/util/mkimage.h |  4 ++--
 util/grub-install-common.c  | 15 +++++++++++---
 util/grub-mkimage.c         | 11 +++++++++++
 util/grub-mkimagexx.c       | 39 ++++++++++++++++++++++++++++++++++++-
 util/mkimage.c              | 13 +++++++------
 6 files changed, 76 insertions(+), 14 deletions(-)

diff --git a/include/grub/util/install.h b/include/grub/util/install.h
index 7d7445af9815..fadcce0fea7e 100644
--- a/include/grub/util/install.h
+++ b/include/grub/util/install.h
@@ -67,6 +67,9 @@
       N_("SBAT metadata"), 0 },                                                
\
   { "disable-shim-lock", GRUB_INSTALL_OPTIONS_DISABLE_SHIM_LOCK, 0, 0, \
       N_("disable shim_lock verifier"), 0 },                           \
+  { "appended-signature-size", GRUB_INSTALL_OPTIONS_APPENDED_SIGNATURE_SIZE,\
+    "SIZE", 0, N_("Add a note segment reserving SIZE bytes for an appended 
signature"), \
+    1},                                                                 \
   { "verbose", 'v', 0, 0,                                              \
     N_("print verbose messages."), 1 }
 
@@ -128,7 +131,8 @@ enum grub_install_options {
   GRUB_INSTALL_OPTIONS_INSTALL_CORE_COMPRESS,
   GRUB_INSTALL_OPTIONS_DTB,
   GRUB_INSTALL_OPTIONS_SBAT,
-  GRUB_INSTALL_OPTIONS_DISABLE_SHIM_LOCK
+  GRUB_INSTALL_OPTIONS_DISABLE_SHIM_LOCK,
+  GRUB_INSTALL_OPTIONS_APPENDED_SIGNATURE_SIZE
 };
 
 extern char *grub_install_source_directory;
@@ -188,7 +192,7 @@ grub_install_generate_image (const char *dir, const char 
*prefix,
                             size_t npubkeys,
                             char *config_path,
                             const struct grub_install_image_target_desc 
*image_target,
-                            int note,
+                            int note, size_t appsig_size,
                             grub_compression_t comp, const char *dtb_file,
                             const char *sbat_path, const int 
disable_shim_lock);
 
diff --git a/include/grub/util/mkimage.h b/include/grub/util/mkimage.h
index 3819a67441c8..6f1da89b9b65 100644
--- a/include/grub/util/mkimage.h
+++ b/include/grub/util/mkimage.h
@@ -51,12 +51,12 @@ grub_mkimage_load_image64 (const char *kernel_path,
                           const struct grub_install_image_target_desc 
*image_target);
 void
 grub_mkimage_generate_elf32 (const struct grub_install_image_target_desc 
*image_target,
-                            int note, char **core_img, size_t *core_size,
+                            int note, size_t appsig_size, char **core_img, 
size_t *core_size,
                             Elf32_Addr target_addr,
                             struct grub_mkimage_layout *layout);
 void
 grub_mkimage_generate_elf64 (const struct grub_install_image_target_desc 
*image_target,
-                            int note, char **core_img, size_t *core_size,
+                            int note, size_t appsig_size, char **core_img, 
size_t *core_size,
                             Elf64_Addr target_addr,
                             struct grub_mkimage_layout *layout);
 
diff --git a/util/grub-install-common.c b/util/grub-install-common.c
index 347558bf5412..b552808df70f 100644
--- a/util/grub-install-common.c
+++ b/util/grub-install-common.c
@@ -461,10 +461,12 @@ static size_t npubkeys;
 static char *sbat;
 static int disable_shim_lock;
 static grub_compression_t compression;
+static size_t appsig_size;
 
 int
 grub_install_parse (int key, char *arg)
 {
+  const char *end;
   switch (key)
     {
     case 'C':
@@ -562,6 +564,12 @@ grub_install_parse (int key, char *arg)
       grub_util_error (_("Unrecognized compression `%s'"), arg);
     case GRUB_INSTALL_OPTIONS_GRUB_MKIMAGE:
       return 1;
+    case GRUB_INSTALL_OPTIONS_APPENDED_SIGNATURE_SIZE:
+      grub_errno = 0;
+      appsig_size = grub_strtol(arg, &end, 10);
+      if (grub_errno)
+        return 0;
+      return 1;
     default:
       return 0;
     }
@@ -661,10 +669,11 @@ grub_install_make_image_wrap_file (const char *dir, const 
char *prefix,
                  " --output '%s' "
                  " --dtb '%s' "
                  "--sbat '%s' "
-                 "--format '%s' --compression '%s' %s %s %s\n",
+                 "--format '%s' --compression '%s' "
+                 "--appended-signature-size %zu %s %s %s\n",
                  dir, prefix,
                  outname, dtb ? : "", sbat ? : "", mkimage_target,
-                 compnames[compression], note ? "--note" : "",
+                 compnames[compression], appsig_size, note ? "--note" : "",
                  disable_shim_lock ? "--disable-shim-lock" : "", s);
   free (s);
 
@@ -675,7 +684,7 @@ grub_install_make_image_wrap_file (const char *dir, const 
char *prefix,
   grub_install_generate_image (dir, prefix, fp, outname,
                               modules.entries, memdisk_path,
                               pubkeys, npubkeys, config_path, tgt,
-                              note, compression, dtb, sbat,
+                              note, appsig_size, compression, dtb, sbat,
                               disable_shim_lock);
   while (dc--)
     grub_install_pop_module ();
diff --git a/util/grub-mkimage.c b/util/grub-mkimage.c
index c0d559937020..49b9410c5fa3 100644
--- a/util/grub-mkimage.c
+++ b/util/grub-mkimage.c
@@ -84,6 +84,7 @@ static struct argp_option options[] = {
   {"sbat", 's', N_("FILE"), 0, N_("SBAT metadata"), 0},
   {"disable-shim-lock", GRUB_INSTALL_OPTIONS_DISABLE_SHIM_LOCK, 0, 0, 
N_("disable shim_lock verifier"), 0},
   {"verbose",     'v', 0,      0, N_("print verbose messages."), 0},
+  {"appended-signature-size", 'S', N_("SIZE"), 0, N_("Add a note segment 
reserving SIZE bytes for an appended signature"), 0},
   { 0, 0, 0, 0, 0, 0 }
 };
 
@@ -128,6 +129,7 @@ struct arguments
   char *sbat;
   int note;
   int disable_shim_lock;
+  size_t appsig_size;
   const struct grub_install_image_target_desc *image_target;
   grub_compression_t comp;
 };
@@ -138,6 +140,7 @@ argp_parser (int key, char *arg, struct argp_state *state)
   /* Get the input argument from argp_parse, which we
      know is a pointer to our arguments structure. */
   struct arguments *arguments = state->input;
+  const char *end;
 
   switch (key)
     {
@@ -170,6 +173,13 @@ argp_parser (int key, char *arg, struct argp_state *state)
       arguments->note = 1;
       break;
 
+    case 'S':
+      grub_errno = 0;
+      arguments->appsig_size = grub_strtol(arg, &end, 10);
+      if (grub_errno)
+        return 0;
+      break;
+
     case 'm':
       if (arguments->memdisk)
        free (arguments->memdisk);
@@ -324,6 +334,7 @@ main (int argc, char *argv[])
                               arguments.memdisk, arguments.pubkeys,
                               arguments.npubkeys, arguments.config,
                               arguments.image_target, arguments.note,
+                              arguments.appsig_size,
                               arguments.comp, arguments.dtb,
                               arguments.sbat, arguments.disable_shim_lock);
 
diff --git a/util/grub-mkimagexx.c b/util/grub-mkimagexx.c
index 1e29e255e8d2..b857c133cb58 100644
--- a/util/grub-mkimagexx.c
+++ b/util/grub-mkimagexx.c
@@ -84,6 +84,15 @@ struct grub_ieee1275_note
   struct grub_ieee1275_note_desc descriptor;
 };
 
+#define GRUB_APPENDED_SIGNATURE_NOTE_NAME "Appended-Signature"
+#define GRUB_APPENDED_SIGNATURE_NOTE_TYPE 0x41536967 /* "ASig" */
+
+struct grub_appended_signature_note
+{
+  Elf32_Nhdr header;
+  char name[ALIGN_UP(sizeof (GRUB_APPENDED_SIGNATURE_NOTE_NAME), 4)];
+};
+
 #define GRUB_XEN_NOTE_NAME "Xen"
 
 struct fixup_block_list
@@ -207,7 +216,7 @@ grub_arm_reloc_jump24 (grub_uint32_t *target, Elf32_Addr 
sym_addr)
 
 void
 SUFFIX (grub_mkimage_generate_elf) (const struct 
grub_install_image_target_desc *image_target,
-                                   int note, char **core_img, size_t 
*core_size,
+                                   int note, size_t appsig_size, char 
**core_img, size_t *core_size,
                                    Elf_Addr target_addr,
                                    struct grub_mkimage_layout *layout)
 {
@@ -221,6 +230,12 @@ SUFFIX (grub_mkimage_generate_elf) (const struct 
grub_install_image_target_desc
   int shnum = 4;
   int string_size = sizeof (".text") + sizeof ("mods") + 1;
 
+  if (appsig_size)
+    {
+      phnum++;
+      footer_size += ALIGN_UP(sizeof (struct grub_appended_signature_note) + 
appsig_size, 4);
+    }
+
   if (image_target->id != IMAGE_LOONGSON_ELF)
     phnum += 2;
 
@@ -484,6 +499,28 @@ SUFFIX (grub_mkimage_generate_elf) (const struct 
grub_install_image_target_desc
       phdr->p_offset = grub_host_to_target32 (header_size + program_size);
     }
 
+  if (appsig_size) {
+    int note_size = ALIGN_UP(sizeof (struct grub_appended_signature_note) + 
appsig_size, 4);
+    struct grub_appended_signature_note *note_ptr = (struct 
grub_appended_signature_note *)
+      (elf_img + program_size + header_size + (note ? sizeof (struct 
grub_ieee1275_note) : 0));
+
+    note_ptr->header.n_namesz = grub_host_to_target32 (sizeof 
(GRUB_APPENDED_SIGNATURE_NOTE_NAME));
+    /* needs to sit at the end, so we round this up and sign some zero padding 
*/
+    note_ptr->header.n_descsz = grub_host_to_target32 (ALIGN_UP(appsig_size, 
4));
+    note_ptr->header.n_type = grub_host_to_target32 
(GRUB_APPENDED_SIGNATURE_NOTE_TYPE);
+    strcpy (note_ptr->name, GRUB_APPENDED_SIGNATURE_NOTE_NAME);
+
+    phdr++;
+    phdr->p_type = grub_host_to_target32 (PT_NOTE);
+    phdr->p_flags = grub_host_to_target32 (PF_R);
+    phdr->p_align = grub_host_to_target32 (image_target->voidp_sizeof);
+    phdr->p_vaddr = 0;
+    phdr->p_paddr = 0;
+    phdr->p_filesz = grub_host_to_target32 (note_size);
+    phdr->p_memsz = 0;
+    phdr->p_offset = grub_host_to_target32 (header_size + program_size + (note 
? sizeof (struct grub_ieee1275_note) : 0));
+  }
+
   {
     char *str_start = (elf_img + sizeof (*ehdr) + phnum * sizeof (*phdr)
                       + shnum * sizeof (*shdr));
diff --git a/util/mkimage.c b/util/mkimage.c
index 21c2db736283..3244ae403701 100644
--- a/util/mkimage.c
+++ b/util/mkimage.c
@@ -869,8 +869,9 @@ grub_install_generate_image (const char *dir, const char 
*prefix,
                             char *memdisk_path, char **pubkey_paths,
                             size_t npubkeys, char *config_path,
                             const struct grub_install_image_target_desc 
*image_target,
-                            int note, grub_compression_t comp, const char 
*dtb_path,
-                            const char *sbat_path, int disable_shim_lock)
+                            int note, size_t appsig_size, grub_compression_t 
comp,
+                            const char *dtb_path, const char *sbat_path, 
+                            int disable_shim_lock)
 {
   char *kernel_img, *core_img;
   size_t total_module_size, core_size;
@@ -1773,11 +1774,11 @@ grub_install_generate_image (const char *dir, const 
char *prefix,
        else
          target_addr = image_target->link_addr;
        if (image_target->voidp_sizeof == 4)
-         grub_mkimage_generate_elf32 (image_target, note, &core_img, 
&core_size,
-                                      target_addr, &layout);
+         grub_mkimage_generate_elf32 (image_target, note, appsig_size, 
&core_img,
+                                      &core_size, target_addr, &layout);
        else
-         grub_mkimage_generate_elf64 (image_target, note, &core_img, 
&core_size,
-                                      target_addr, &layout);
+         grub_mkimage_generate_elf64 (image_target, note, appsig_size, 
&core_img,
+                                      &core_size, target_addr, &layout);
       }
       break;
     }
-- 
2.32.0