[RFC PATCH v2 1/1] kern/dl: Add module version check

[Zhang Boyang]

This patch add version information to GRUB modules. Specifically,
PACKAGE_VERSION is embedded as null-terminated string in .modver
section. This string is checked at module loading time.

If GRUB is locked down, modules with mismatched version will be
rejected. This is necessary for implementing external signed modules
securely (in future).

For compatibility reasons, if GRUB isn't locked down, modules can still
be loaded even if they have mismatched version. A warning message will
be emited in that situation.

It should be pointed out that the version string is only consisted of
PACKAGE_VERSION. Any difference not reflected in PACKAGE_VERSION is not
noticed by version check (e.g. configure options).

Link: https://lists.gnu.org/archive/html/grub-devel/2022-12/msg00228.html
Link: https://lists.gnu.org/archive/html/grub-devel/2022-12/msg00229.html
Signed-off-by: Zhang Boyang <zhangboyang.id@gmail.com>
---
 grub-core/Makefile.am         |  2 +-
 grub-core/genmod.sh.in        | 28 +++++++++++++++++-----------
 grub-core/kern/dl.c           | 33 +++++++++++++++++++++++++++++++++
 util/grub-module-verifierXX.c | 10 ++++++++++
 4 files changed, 61 insertions(+), 12 deletions(-)

diff --git a/grub-core/Makefile.am b/grub-core/Makefile.am
index 80e7a83ed..d76aa80f4 100644
--- a/grub-core/Makefile.am
+++ b/grub-core/Makefile.am
@@ -40,7 +40,7 @@ gentrigtables$(BUILD_EXEEXT): gentrigtables.c
 CLEANFILES += gentrigtables$(BUILD_EXEEXT)
 
 build-grub-module-verifier$(BUILD_EXEEXT): 
$(top_srcdir)/util/grub-module-verifier.c 
$(top_srcdir)/util/grub-module-verifier32.c 
$(top_srcdir)/util/grub-module-verifier64.c 
$(top_srcdir)/grub-core/kern/emu/misc.c $(top_srcdir)/util/misc.c
-       $(BUILD_CC) -o $@ -I$(top_srcdir)/include $(BUILD_CFLAGS) 
$(BUILD_CPPFLAGS) $(BUILD_LDFLAGS) -DGRUB_BUILD=1 -DGRUB_UTIL=1 
-DGRUB_BUILD_PROGRAM_NAME=\"build-grub-module-verifier\" $^
+       $(BUILD_CC) -o $@ -I$(top_srcdir)/include $(BUILD_CFLAGS) 
$(BUILD_CPPFLAGS) $(BUILD_LDFLAGS) -DGRUB_BUILD=1 -DGRUB_UTIL=1 
-DGRUB_BUILD_PROGRAM_NAME=\"build-grub-module-verifier\" 
-DPACKAGE_VERSION=\"$(PACKAGE_VERSION)\" $^
 CLEANFILES += build-grub-module-verifier$(BUILD_EXEEXT)
 
 # trigtables.c
diff --git a/grub-core/genmod.sh.in b/grub-core/genmod.sh.in
index e57c4d920..58a4cdcbe 100644
--- a/grub-core/genmod.sh.in
+++ b/grub-core/genmod.sh.in
@@ -36,22 +36,25 @@ deps=`grep ^$modname: $moddep | sed s@^.*:@@`
 rm -f $tmpfile $outfile
 
 if test x@TARGET_APPLE_LINKER@ != x1; then
-    # stripout .modname and .moddeps sections from input module
-    @TARGET_OBJCOPY@ -R .modname -R .moddeps $infile $tmpfile
+    # stripout .modname and .moddeps and .modver sections from input module
+    @TARGET_OBJCOPY@ -R .modname -R .moddeps -R .modver $infile $tmpfile
 
-    # Attach .modname and .moddeps sections
+    # Attach .modname and .moddeps and .modver sections
     t1=`mktemp "${TMPDIR:-/tmp}/tmp.XXXXXXXXXX"` || exit 1
     printf "$modname\0" >$t1
 
     t2=`mktemp "${TMPDIR:-/tmp}/tmp.XXXXXXXXXX"` || exit 1
     for dep in $deps; do printf "$dep\0" >> $t2; done
 
+    t3=`mktemp "${TMPDIR:-/tmp}/tmp.XXXXXXXXXX"` || exit 1
+    printf "@PACKAGE_VERSION@\0" >$t3
+
     if test -n "$deps"; then
-       @TARGET_OBJCOPY@ --add-section .modname=$t1 --add-section .moddeps=$t2 
$tmpfile
+       @TARGET_OBJCOPY@ --add-section .modname=$t1 --add-section .moddeps=$t2 
--add-section .modver=$t3 $tmpfile
     else
-       @TARGET_OBJCOPY@ --add-section .modname=$t1 $tmpfile
+       @TARGET_OBJCOPY@ --add-section .modname=$t1 --add-section .modver=$t3 
$tmpfile
     fi
-    rm -f $t1 $t2
+    rm -f $t1 $t2 $t3
 
        if test x@platform@ != xemu; then
            @TARGET_STRIP@ --strip-unneeded \
@@ -71,23 +74,26 @@ else
     tmpfile2=${outfile}.tmp2
     t1=${outfile}.t1.c
     t2=${outfile}.t2.c
+    t3=${outfile}.t3.c
 
     # remove old files if any
-    rm -f $t1 $t2
+    rm -f $t1 $t2 $t3
 
     cp $infile $tmpfile
 
-    # Attach .modname and .moddeps sections
+    # Attach .modname and .moddeps and .modver sections
     echo "char modname[]  __attribute__ ((section(\"_modname, _modname\"))) = 
\"$modname\";" >$t1
 
     for dep in $deps; do echo "char moddep_$dep[] __attribute__ 
((section(\"_moddeps, _moddeps\"))) = \"$dep\";" >>$t2; done
 
+    echo "char modver[]  __attribute__ ((section(\"_modver, _modver\"))) = 
\"@PACKAGE_VERSION@\";" >$t3
+
     if test -n "$deps"; then
-       @TARGET_CC@ @TARGET_LDFLAGS@ -ffreestanding -nostdlib -o $tmpfile2 $t1 
$t2 $tmpfile -Wl,-r
+       @TARGET_CC@ @TARGET_LDFLAGS@ -ffreestanding -nostdlib -o $tmpfile2 $t1 
$t2 $t3 $tmpfile -Wl,-r
     else
-       @TARGET_CC@ @TARGET_LDFLAGS@ -ffreestanding -nostdlib -o $tmpfile2 $t1 
$tmpfile -Wl,-r
+       @TARGET_CC@ @TARGET_LDFLAGS@ -ffreestanding -nostdlib -o $tmpfile2 $t1 
$t3 $tmpfile -Wl,-r
     fi
-    rm -f $t1 $t2 $tmpfile
+    rm -f $t1 $t2 $t3 $tmpfile
     mv $tmpfile2 $tmpfile
 
        cp $tmpfile $tmpfile.bin
diff --git a/grub-core/kern/dl.c b/grub-core/kern/dl.c
index e447fd0fa..0292b162c 100644
--- a/grub-core/kern/dl.c
+++ b/grub-core/kern/dl.c
@@ -32,6 +32,7 @@
 #include <grub/env.h>
 #include <grub/cache.h>
 #include <grub/i18n.h>
+#include <grub/lockdown.h>
 
 /* Platforms where modules are in a readonly area of memory.  */
 #if defined(GRUB_MACHINE_QEMU)
@@ -475,6 +476,37 @@ grub_dl_check_license (grub_dl_t mod, Elf_Ehdr *e)
                     (char *) e + s->sh_offset);
 }
 
+static grub_err_t
+grub_dl_check_version (grub_dl_t mod, Elf_Ehdr *e)
+{
+  Elf_Shdr *s = grub_dl_find_section (e, ".modver");
+  const char *modver;
+  
+  modver = _("(unknown)");
+  if (s == NULL)
+    goto fail;
+
+  modver = (char *) e + s->sh_offset;
+  if (grub_strcmp (modver, PACKAGE_VERSION) != 0)
+    goto fail;
+
+  return GRUB_ERR_NONE;
+
+fail:
+  if (grub_is_lockdown () == GRUB_LOCKDOWN_ENABLED)
+    {
+      return grub_error (GRUB_ERR_BAD_MODULE,
+                        N_("refuse to load module %.63s of incorrect version: 
%.63s != %s"),
+                        mod->name, modver, PACKAGE_VERSION);
+    }
+  else
+    {
+      grub_printf_ (N_("warning: module %.63s has incorrect version: %.63s != 
%s\n"),
+                   mod->name, modver, PACKAGE_VERSION);
+      return GRUB_ERR_NONE;
+    }
+}
+
 static grub_err_t
 grub_dl_resolve_name (grub_dl_t mod, Elf_Ehdr *e)
 {
@@ -650,6 +682,7 @@ grub_dl_load_core_noinit (void *addr, grub_size_t size)
      Be sure to understand your license obligations.
   */
   if (grub_dl_resolve_name (mod, e)
+      || grub_dl_check_version (mod, e)
       || grub_dl_check_license (mod, e)
       || grub_dl_resolve_dependencies (mod, e)
       || grub_dl_load_segments (mod, e)
diff --git a/util/grub-module-verifierXX.c b/util/grub-module-verifierXX.c
index d5907f268..fde111016 100644
--- a/util/grub-module-verifierXX.c
+++ b/util/grub-module-verifierXX.c
@@ -491,8 +491,18 @@ SUFFIX(grub_module_verify) (const char * const filename,
   check_license (filename, arch, e);
 
   Elf_Shdr *s;
+  const char *modver;
   const char *modname;
 
+  s = find_section (arch, e, ".modver");
+  if (!s)
+    grub_util_error ("%s: no module version found", filename);
+
+  modver = (const char *) e + grub_target_to_host (s->sh_offset);
+
+  if (strcmp (modver, PACKAGE_VERSION) != 0)
+    grub_util_error ("%s: bad module version", filename);
+
   s = find_section (arch, e, ".modname");
   if (!s)
     grub_util_error ("%s: no module name found", filename);
-- 
2.30.2