kern/efi: Add initial stack protector implementation

It works only on UEFI platforms but can be quite easily extended to
others architectures and platforms if needed.

Signed-off-by: Chris Coulson <chris.coulson@canonical.com>
Signed-off-by: Daniel Kiper <daniel.kiper@oracle.com>
Reviewed-by: Marco A Benatto <mbenatto@redhat.com>
Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>

acinclude.m4

@@ -305,9 +305,9 @@ fi
 ])
 
 
-dnl Check if the C compiler supports `-fstack-protector'.
+dnl Check if the C compiler supports the stack protector
 AC_DEFUN([grub_CHECK_STACK_PROTECTOR],[
-[# Smashing stack protector.
+[# Stack smashing protector.
 ssp_possible=yes]
 AC_MSG_CHECKING([whether `$CC' accepts `-fstack-protector'])
 # Is this a reliable test case?
@@ -324,6 +324,40 @@ else
   ssp_possible=no]
   AC_MSG_RESULT([no])
 [fi]
+[# Strong stack smashing protector.
+ssp_strong_possible=yes]
+AC_MSG_CHECKING([whether `$CC' accepts `-fstack-protector-strong'])
+# Is this a reliable test case?
+AC_LANG_CONFTEST([AC_LANG_SOURCE([[
+void foo (void) { volatile char a[8]; a[3]; }
+]])])
+[# `$CC -c -o ...' might not be portable.  But, oh, well...  Is calling
+# `ac_compile' like this correct, after all?
+if eval "$ac_compile -S -fstack-protector-strong -o conftest.s" 2> /dev/null; then]
+  AC_MSG_RESULT([yes])
+  [# Should we clear up other files as well, having called `AC_LANG_CONFTEST'?
+  rm -f conftest.s
+else
+  ssp_strong_possible=no]
+  AC_MSG_RESULT([no])
+[fi]
+[# Global stack smashing protector.
+ssp_global_possible=yes]
+AC_MSG_CHECKING([whether `$CC' accepts `-mstack-protector-guard=global'])
+# Is this a reliable test case?
+AC_LANG_CONFTEST([AC_LANG_SOURCE([[
+void foo (void) { volatile char a[8]; a[3]; }
+]])])
+[# `$CC -c -o ...' might not be portable.  But, oh, well...  Is calling
+# `ac_compile' like this correct, after all?
+if eval "$ac_compile -S -fstack-protector -mstack-protector-guard=global -o conftest.s" 2> /dev/null; then]
+  AC_MSG_RESULT([yes])
+  [# Should we clear up other files as well, having called `AC_LANG_CONFTEST'?
+  rm -f conftest.s
+else
+  ssp_global_possible=no]
+  AC_MSG_RESULT([no])
+[fi]
 ])
 
 dnl Check if the C compiler supports `-mstack-arg-probe' (Cygwin).

configure.ac

@@ -1312,12 +1312,41 @@ fi]
 
 CFLAGS="$TARGET_CFLAGS"
 
-# Smashing stack protector.
+# Stack smashing protector.
 grub_CHECK_STACK_PROTECTOR
-# Need that, because some distributions ship compilers that include
-# `-fstack-protector' in the default specs.
-if test "x$ssp_possible" = xyes; then
+AC_ARG_ENABLE([stack-protector],
+	      AS_HELP_STRING([--enable-stack-protector],
+			     [enable the stack protector]),
+	      [],
+	      [enable_stack_protector=no])
+if test "x$enable_stack_protector" = xno; then
+  if test "x$ssp_possible" = xyes; then
+    # Need that, because some distributions ship compilers that include
+    # `-fstack-protector' in the default specs.
     TARGET_CFLAGS="$TARGET_CFLAGS -fno-stack-protector"
+  fi
+elif test "x$platform" != xefi; then
+  AC_MSG_ERROR([--enable-stack-protector is only supported on EFI platforms])
+elif test "x$ssp_global_possible" != xyes; then
+  AC_MSG_ERROR([--enable-stack-protector is not supported (compiler doesn't support -mstack-protector-guard=global)])
+else
+  TARGET_CFLAGS="$TARGET_CFLAGS -mstack-protector-guard=global"
+  if test "x$enable_stack_protector" = xyes; then
+    if test "x$ssp_possible" != xyes; then
+      AC_MSG_ERROR([--enable-stack-protector is not supported (compiler doesn't support -fstack-protector)])
+    fi
+    TARGET_CFLAGS="$TARGET_CFLAGS -fstack-protector"
+  elif test "x$enable_stack_protector" = xstrong; then
+    if test "x$ssp_strong_possible" != xyes; then
+      AC_MSG_ERROR([--enable-stack-protector=strong is not supported (compiler doesn't support -fstack-protector-strong)])
+    fi
+    TARGET_CFLAGS="$TARGET_CFLAGS -fstack-protector-strong"
+  else
+    # Note, -fstack-protector-all requires that the protector is disabled for
+    # functions that appear in the call stack when the canary is initialized.
+    AC_MSG_ERROR([invalid value $enable_stack_protector for --enable-stack-protector])
+  fi
+  TARGET_CPPFLAGS="$TARGET_CPPFLAGS -DGRUB_STACK_PROTECTOR=1"
 fi
 
 CFLAGS="$TARGET_CFLAGS"
@@ -2132,5 +2161,10 @@ echo "Without liblzma (no support for XZ-compressed mips images) ($liblzma_excus
 else
 echo "With liblzma from $LIBLZMA (support for XZ-compressed mips images)"
 fi
+if test "x$enable_stack_protector" != xno; then
+echo "With stack smashing protector: Yes"
+else
+echo "With stack smashing protector: No"
+fi
 echo "*******************************************************"
 ]

grub-core/Makefile.am

@@ -90,6 +90,7 @@ endif
 KERNEL_HEADER_FILES += $(top_srcdir)/include/grub/mm.h
 KERNEL_HEADER_FILES += $(top_srcdir)/include/grub/parser.h
 KERNEL_HEADER_FILES += $(top_srcdir)/include/grub/partition.h
+KERNEL_HEADER_FILES += $(top_srcdir)/include/grub/stack_protector.h
 KERNEL_HEADER_FILES += $(top_srcdir)/include/grub/term.h
 KERNEL_HEADER_FILES += $(top_srcdir)/include/grub/time.h
 KERNEL_HEADER_FILES += $(top_srcdir)/include/grub/verify.h

grub-core/kern/efi/init.c

@@ -27,6 +27,58 @@
 #include <grub/env.h>
 #include <grub/mm.h>
 #include <grub/kernel.h>
+#include <grub/stack_protector.h>
+
+#ifdef GRUB_STACK_PROTECTOR
+
+static grub_efi_guid_t rng_protocol_guid = GRUB_EFI_RNG_PROTOCOL_GUID;
+
+/*
+ * Don't put this on grub_efi_init()'s local stack to avoid it
+ * getting a stack check.
+ */
+static grub_efi_uint8_t stack_chk_guard_buf[32];
+
+grub_addr_t __stack_chk_guard;
+
+void __attribute__ ((noreturn))
+__stack_chk_fail (void)
+{
+  /*
+   * Assume it's not safe to call into EFI Boot Services. Sorry, that
+   * means no console message here.
+   */
+  do
+    {
+      /* Do not optimize out the loop. */
+      asm volatile ("");
+    }
+  while (1);
+}
+
+static void
+stack_protector_init (void)
+{
+  grub_efi_rng_protocol_t *rng;
+
+  /* Set up the stack canary. Make errors here non-fatal for now. */
+  rng = grub_efi_locate_protocol (&rng_protocol_guid, NULL);
+  if (rng != NULL)
+    {
+      grub_efi_status_t status;
+
+      status = efi_call_4 (rng->get_rng, rng, NULL, sizeof (stack_chk_guard_buf),
+			   stack_chk_guard_buf);
+      if (status == GRUB_EFI_SUCCESS)
+	grub_memcpy (&__stack_chk_guard, stack_chk_guard_buf, sizeof (__stack_chk_guard));
+    }
+}
+#else
+static void
+stack_protector_init (void)
+{
+}
+#endif
 
 grub_addr_t grub_modbase;
 
@@ -38,6 +90,8 @@ grub_efi_init (void)
      messages.  */
   grub_console_init ();
 
+  stack_protector_init ();
+
   /* Initialize the memory management system.  */
   grub_efi_mm_init ();
 

include/grub/efi/api.h

@@ -344,6 +344,11 @@
     { 0xab, 0xb6, 0x3d, 0xd8, 0x10, 0xdd, 0x8b, 0x23 } \
   }
 
+#define GRUB_EFI_RNG_PROTOCOL_GUID \
+  { 0x3152bca5, 0xeade, 0x433d, \
+    { 0x86, 0x2e, 0xc0, 0x1c, 0xdc, 0x29, 0x1f, 0x44 } \
+  }
+
 struct grub_efi_sal_system_table
 {
   grub_uint32_t signature;
@@ -1705,6 +1710,20 @@ struct grub_efi_shim_lock_protocol
 };
 typedef struct grub_efi_shim_lock_protocol grub_efi_shim_lock_protocol_t;
 
+typedef grub_efi_guid_t grub_efi_rng_algorithm_t;
+
+struct grub_efi_rng_protocol
+{
+  grub_efi_status_t (*get_info) (struct grub_efi_rng_protocol *this,
+				 grub_efi_uintn_t *rng_algorithm_list_size,
+				 grub_efi_rng_algorithm_t *rng_algorithm_list);
+  grub_efi_status_t (*get_rng) (struct grub_efi_rng_protocol *this,
+				grub_efi_rng_algorithm_t *rng_algorithm,
+				grub_efi_uintn_t rng_value_length,
+				grub_efi_uint8_t *rng_value);
+};
+typedef struct grub_efi_rng_protocol grub_efi_rng_protocol_t;
+
 #if (GRUB_TARGET_SIZEOF_VOID_P == 4) || defined (__ia64__) \
   || defined (__aarch64__) || defined (__MINGW64__) || defined (__CYGWIN__) \
   || defined(__riscv)

include/grub/stack_protector.h

@@ -0,0 +1,30 @@
+/*
+ *  GRUB  --  GRand Unified Bootloader
+ *  Copyright (C) 2021  Free Software Foundation, Inc.
+ *
+ *  GRUB is free software: you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation, either version 3 of the License, or
+ *  (at your option) any later version.
+ *
+ *  GRUB is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License
+ *  along with GRUB.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#ifndef GRUB_STACK_PROTECTOR_H
+#define GRUB_STACK_PROTECTOR_H	1
+
+#include <grub/symbol.h>
+#include <grub/types.h>
+
+#ifdef GRUB_STACK_PROTECTOR
+extern grub_addr_t EXPORT_VAR (__stack_chk_guard);
+extern void __attribute__ ((noreturn)) EXPORT_FUNC (__stack_chk_fail) (void);
+#endif
+
+#endif /* GRUB_STACK_PROTECTOR_H */