Kernel+LibC: Build with basic -fstack-protector support

Use simple stack cookies to try to provoke an assertion failure on
stack overflow.

This is far from perfect, since we use a constant cookie instead of
generating a random one on startup, but it can still help us catch
bugs, which is the primary concern right now. :^)

Kernel/StdLib.cpp

@@ -183,4 +183,12 @@ void free(void* p)
 {
  return kfree(p);
 }
+
+extern u32 __stack_chk_guard;
+u32 __stack_chk_guard = (u32)0xc0000c13;
+
+[[noreturn]] void __stack_chk_fail()
+{
+ ASSERT_NOT_REACHED();
+}
 }

Libraries/LibC/crt0.cpp

@@ -1,3 +1,4 @@
+#include <AK/Types.h>
 #include <assert.h>
 #include <stdio.h>
 #include <stdlib.h>
@@ -51,4 +52,12 @@ int _start(int argc, char** argv, char** env)
 void __cxa_atexit()
 {
 }
+
+extern u32 __stack_chk_guard;
+u32 __stack_chk_guard = (u32)0xc0000c13;
+
+[[noreturn]] void __stack_chk_fail()
+{
+ ASSERT_NOT_REACHED();
+}
 }

Makefile.common

@@ -1,7 +1,7 @@
 ARCH_FLAGS =
 STANDARD_FLAGS = -std=c++17 -Wno-sized-deallocation -fno-sized-deallocation
 WARNING_FLAGS = -Werror -Wextra -Wall -Wno-nonnull-compare -Wno-deprecated-copy -Wno-address-of-packed-member -Wundef -Wcast-qual -Wwrite-strings -Wimplicit-fallthrough -Wno-expansion-to-defined
-FLAVOR_FLAGS = -fno-exceptions -fno-rtti
+FLAVOR_FLAGS = -fno-exceptions -fno-rtti -fstack-protector
 OPTIMIZATION_FLAGS = -Os
 
 MAKEFILE_PATH := $(abspath $(lastword $(MAKEFILE_LIST)))