Build + LibC: Enable -fstack-protector-strong in user space

Modify the user mode runtime to insert stack canaries to find stack corruptions.

The `-fstack-protector-strong` variant was chosen because it catches more
issues than vanilla `-fstack-protector`, but doesn't have substantial
performance impact like `-fstack-protector-all`.

Details:

    -fstack-protector enables stack protection for vulnerable functions that contain:

    * A character array larger than 8 bytes.
    * An 8-bit integer array larger than 8 bytes.
    * A call to alloca() with either a variable size or a constant size bigger than 8 bytes.

    -fstack-protector-strong enables stack protection for vulnerable functions that contain:

    * An array of any size and type.
    * A call to alloca().
    * A local variable that has its address taken.

Example of it catching corrupting in the `stack-smash` test:
```
courage ~ $ ./user/Tests/LibC/stack-smash
[+] Starting the stack smash ...
Error: Stack protector failure, stack smashing detected!
Shell: Job 1 (/usr/Tests/LibC/stack-smash) Aborted
```

Libraries/LibC/CMakeLists.txt

@@ -70,13 +70,21 @@ add_custom_command(
     COMMAND ${INSTALL_COMMAND} -D $<TARGET_OBJECTS:crt0_shared> ${CMAKE_INSTALL_PREFIX}/usr/lib/crt0_shared.o
 )
 
+set_source_files_properties (ssp.cpp PROPERTIES COMPILE_FLAGS
+    "-fno-stack-protector")
+add_library(ssp STATIC ssp.cpp)
+add_custom_command(
+    TARGET ssp
+    COMMAND ${INSTALL_COMMAND} -D $<TARGET_OBJECTS:ssp> ${CMAKE_INSTALL_PREFIX}/usr/lib/ssp.o
+)
+
 set(SOURCES ${LIBC_SOURCES} ${AK_SOURCES} ${ELF_SOURCES})
 
 serenity_libc_static(LibCStatic c)
-target_link_libraries(LibCStatic crt0)
+target_link_libraries(LibCStatic crt0 ssp)
 add_dependencies(LibCStatic LibM)
 
 set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -static-libstdc++")
 serenity_libc(LibC c)
-target_link_libraries(LibC crt0)
+target_link_libraries(LibC crt0 ssp)
 add_dependencies(LibC LibM)

Libraries/LibC/cxxabi.cpp

@@ -24,7 +24,6 @@
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
-#include <AK/Types.h>
 #include <assert.h>
 #include <stdio.h>
 #include <stdlib.h>
@@ -87,11 +86,4 @@ void __cxa_finalize(void* dso_handle)
     ASSERT_NOT_REACHED();
 }
 
-extern u32 __stack_chk_guard;
-u32 __stack_chk_guard = (u32)0xc6c7c8c9;
-
-[[noreturn]] void __stack_chk_fail()
-{
-    ASSERT_NOT_REACHED();
-}
 } // extern "C"

Libraries/LibC/ssp.cpp

@@ -0,0 +1,55 @@
+/*
+ * Copyright (c) 2021, Brian Gianforcaro <b.gianfo@gmail.com>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <AK/Types.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <sys/internals.h>
+#include <unistd.h>
+
+#if defined __SSP__ || defined __SSP_ALL__
+#    error "file must not be compiled with stack protection enabled on it. Use -fno-stack-protector"
+#endif
+
+extern "C" {
+
+extern u32 __stack_chk_guard;
+u32 __stack_chk_guard = (u32)0xc6c7c8c9;
+
+[[noreturn]] void __stack_chk_fail()
+{
+    dbgprintf("Error: USERSPACE(%d) Stack protector failure, stack smashing detected!\n", getpid());
+    if (__stdio_is_initialized)
+        fprintf(stderr, "Error: Stack protector failure, stack smashing detected!\n");
+    abort();
+}
+
+[[noreturn]] void __stack_chk_fail_local()
+{
+    __stack_chk_fail();
+}
+
+} // extern "C"

Libraries/LibC/sys/internals.h

@@ -43,5 +43,6 @@ int __cxa_atexit(AtExitFunction exit_function, void* parameter, void* dso_handle
 void __cxa_finalize(void* dso_handle);
 [[noreturn]] void __cxa_pure_virtual() __attribute__((weak));
 [[noreturn]] void __stack_chk_fail();
+[[noreturn]] void __stack_chk_fail_local();
 
 __END_DECLS