MIPS: ZBOOT: implement stack protector in compressed boot phase

This patch implements the stack protector code in MIPS compressed boot
phase based on the same code added to arm in commit
8779657 "stackprotector: Introduce
CONFIG_CC_STACKPROTECTOR_STRONG" by Kees Cook <keescook@chromium.org>

Signed-off-by: Ben Chan <benchan@chromium.org>
Cc: Kees Cook <keescook@chromium.org>
Cc: Olof Johansson <olofj@chromium.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/7175/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/boot/compressed/decompress.c

@@ -67,10 +67,24 @@ void error(char *x)
 #include "../../../../lib/decompress_unxz.c"
 #endif
 
+unsigned long __stack_chk_guard;
+
+void __stack_chk_guard_setup(void)
+{
+	__stack_chk_guard = 0x000a0dff;
+}
+
+void __stack_chk_fail(void)
+{
+	error("stack-protector: Kernel stack is corrupted\n");
+}
+
 void decompress_kernel(unsigned long boot_heap_start)
 {
 	unsigned long zimage_start, zimage_size;
 
+	__stack_chk_guard_setup();
+
 	zimage_start = (unsigned long)(&__image_begin);
 	zimage_size = (unsigned long)(&__image_end) -
 	    (unsigned long)(&__image_begin);