[PATCH] kern/efi: Log a console error during a stack check failure

[Chris Coulson]

The initial implementation of the stack protector just busy looped
in __stack_chk_fail in order to reduce the amount of code being
executed after the stack has been compromised because of a lack of
firmware memory protections. With future firmware implementations
incorporating memory protections such as W^X, call in to boot services
when an error occurs in order to log a message to the console before
automatically rebooting the machine.

Signed-off-by: Chris Coulson <chris.coulson@canonical.com>
---
 grub-core/Makefile.core.def |  4 +++-
 grub-core/kern/efi/init.c   | 23 +++++++++++++++++++++--
 2 files changed, 24 insertions(+), 3 deletions(-)

diff --git a/grub-core/Makefile.core.def b/grub-core/Makefile.core.def
index ac00cc8a2..7e831d124 100644
--- a/grub-core/Makefile.core.def
+++ b/grub-core/Makefile.core.def
@@ -50,12 +50,14 @@ kernel = {
   nostrip = emu;
 
   emu_ldflags              = '-Wl,-r';
+  i386_efi_cflags          = '-fshort-wchar';
   i386_efi_ldflags         = '-Wl,-r';
   i386_efi_stripflags      = '--strip-unneeded -K start -R .note -R .comment 
-R .note.gnu.gold-version';
+  x86_64_efi_cflags        = '-fshort-wchar';
   x86_64_efi_ldflags       = '-Wl,-r';
   x86_64_efi_stripflags    = '--strip-unneeded -K start -R .note -R .comment 
-R .note.gnu.gold-version';
 
-  ia64_efi_cflags = '-fno-builtin -fpic -minline-int-divide-max-throughput';
+  ia64_efi_cflags = '-fshort-wchar -fno-builtin -fpic 
-minline-int-divide-max-throughput';
   ia64_efi_ldflags = '-Wl,-r';
   ia64_efi_stripflags = '--strip-unneeded -K start -R .note -R .comment -R 
.note.gnu.gold-version';
 
diff --git a/grub-core/kern/efi/init.c b/grub-core/kern/efi/init.c
index 7facacf09..7cb3f77e0 100644
--- a/grub-core/kern/efi/init.c
+++ b/grub-core/kern/efi/init.c
@@ -31,6 +31,11 @@
 
 #ifdef GRUB_STACK_PROTECTOR
 
+static const grub_efi_char16_t stack_chk_fail_msg[] =
+  L"* GRUB: STACK SMASHING DETECTED!!! *\r\n"
+  L"* GRUB: ABORTED!!! *\r\n"
+  L"* GRUB: REBOOTING IN 5 SECONDS... *\r\n";
+
 static grub_efi_guid_t rng_protocol_guid = GRUB_EFI_RNG_PROTOCOL_GUID;
 
 /*
@@ -44,9 +49,23 @@ grub_addr_t __stack_chk_guard;
 void __attribute__ ((noreturn))
 __stack_chk_fail (void)
 {
+  grub_efi_simple_text_output_interface_t *o;
+
+  /*
+   * Use ConOut here rather than StdErr. StdErr only goes to
+   * the serial console, at least on EDK2.
+   */
+  o = grub_efi_system_table->con_out;
+  efi_call_2 (o->output_string, o, stack_chk_fail_msg);
+
+  efi_call_1 (grub_efi_system_table->boot_services->stall, 5000000);
+  efi_call_4 (grub_efi_system_table->runtime_services->reset_system,
+             GRUB_EFI_RESET_SHUTDOWN, GRUB_EFI_ABORTED, 0, NULL);
+
   /*
-   * Assume it's not safe to call into EFI Boot Services. Sorry, that
-   * means no console message here.
+   * We shouldn't get here. It's unsafe to return because the stack
+   * is compromised and this function is noreturn, so just busy
+   * loop forever.
    */
   do
     {
-- 
2.35.1