sh/boot: add static stack-protector to pre-kernel

The sh decompressor code triggers stack-protector code generation when
using CONFIG_CC_STACKPROTECTOR_STRONG.  As done for arm and mips, add a
simple static stack-protector canary.  As this wasn't protected before,
the risk of using a weak canary is minimized.  Once the kernel is
actually up, a better canary is chosen.

Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Kees Cook <[email protected]>
Cc: Yoshinori Sato <[email protected]>
Cc: Rich Felker <[email protected]>
Cc: Al Viro <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Laura Abbott <[email protected]>
Cc: Masahiro Yamada <[email protected]>
Cc: Michal Marek <[email protected]>
Cc: Nicholas Piggin <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

arch/sh/boot/compressed/misc.c

@@ -104,6 +104,18 @@ static void error(char *x)
 	while(1);	/* Halt */
 }
 
+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");
+}
+
 #ifdef CONFIG_SUPERH64
 #define stackalign	8
 #else
@@ -118,6 +130,8 @@ void decompress_kernel(void)
 {
 	unsigned long output_addr;
 
+	__stack_chk_guard_setup();
+
 #ifdef CONFIG_SUPERH64
 	output_addr = (CONFIG_MEMORY_START + 0x2000);
 #else