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
```

CMakeLists.txt

@@ -125,9 +125,7 @@ if (CMAKE_SYSTEM_NAME MATCHES Darwin)
     set(CMAKE_SKIP_RPATH TRUE)
 endif()
 
-#FIXME: -fstack-protector
-
-add_compile_options(-Os -g1 -fno-exceptions -Wno-address-of-packed-member -Wundef -Wcast-qual -Wwrite-strings -Wimplicit-fallthrough -Wno-nonnull-compare -Wno-deprecated-copy -Wno-expansion-to-defined)
+add_compile_options(-Os -g1 -fno-exceptions -fstack-protector-strong -Wno-address-of-packed-member -Wundef -Wcast-qual -Wwrite-strings -Wimplicit-fallthrough -Wno-nonnull-compare -Wno-deprecated-copy -Wno-expansion-to-defined)
 add_compile_options(-ffile-prefix-map=${CMAKE_SOURCE_DIR}=.)
 
 add_compile_definitions(DEBUG SANITIZE_PTRS)

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

Userland/DynamicLoader/CMakeLists.txt

@@ -18,6 +18,9 @@ set(SOURCES ${LOADER_SOURCES} ${AK_SOURCES} ${ELF_SOURCES} ${LIBC_SOURCES1} ${LI
 
 set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -fno-rtti -nostdlib -pie -fpic -DNO_TLS")
 
+set_source_files_properties (../../Libraries/LibC/ssp.cpp PROPERTIES COMPILE_FLAGS
+    "-fno-stack-protector")
+
 add_executable(Loader.so ${SOURCES})
 target_link_options(Loader.so PRIVATE LINKER:--no-dynamic-linker)
 install(TARGETS Loader.so RUNTIME DESTINATION usr/lib/)

Userland/Tests/LibC/stack-smash.cpp

@@ -0,0 +1,54 @@
+/*
+ * 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 <cstdio>
+
+// Note: Needs to be 'noline' so stack canary isn't optimized out.
+static void __attribute__((noinline)) smasher(char* string)
+{
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Warray-bounds"
+    for (int i = 0; i < 256; i++) {
+        string[i] = 'A';
+    }
+#pragma GCC diagnostic pop
+}
+
+// Note: Needs to be 'noline' so stack canary isn't optimized out.
+static void __attribute__((noinline)) stack_to_smash()
+{
+    char string[8] = {};
+    smasher(string);
+}
+
+int main()
+{
+    puts("[+] Starting the stack smash...");
+    stack_to_smash();
+    puts("[+] Stack smash wasn't detected!");
+
+    return 0;
+}