zboot: fix stack protector in compressed boot phase

Calling __stack_chk_guard_setup() in decompress_kernel() is too late
that stack checking always fails for decompress_kernel() itself. So
remove __stack_chk_guard_setup() and initialize __stack_chk_guard before
we call decompress_kernel().

Original code comes from ARM but also used for MIPS and SH, so fix them
together. If without this fix, compressed booting of these archs will
fail because stack checking is enabled by default (>=4.16).

Link: http://lkml.kernel.org/r/[e-mail]
Fixes: 8779657d29c0 ("stackprotector: Introduce CONFIG_CC_STACKPROTECTOR_STRONG")
Signed-off-by: Huacai Chen <[e-mail]>
Acked-by: James Hogan <[e-mail]>
Acked-by: Kees Cook <[e-mail]>
Acked-by: Rich Felker <[e-mail]>
Cc: Ralf Baechle <[e-mail]>
Cc: Russell King <[e-mail]>
Cc: Yoshinori Sato <[e-mail]>
Cc: Ingo Molnar <[e-mail]>
Cc: <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

arch/arm/boot/compressed/misc.c

···
 	error("Attempting division by 0!");
 }
 
-unsigned long __stack_chk_guard;
-
-void __stack_chk_guard_setup(void)
-{
-	__stack_chk_guard = 0x000a0dff;
-}
+const unsigned long __stack_chk_guard = 0x000a0dff;
 
 void __stack_chk_fail(void)
 {
···
 		int arch_id)
 {
 	int ret;
-
-	__stack_chk_guard_setup();
 
 	output_data		= (unsigned char *)output_start;
 	free_mem_ptr		= free_mem_ptr_p;

arch/mips/boot/compressed/decompress.c

···
 #include "../../../../lib/decompress_unxz.c"
 #endif
 
-unsigned long __stack_chk_guard;
-
-void __stack_chk_guard_setup(void)
-{
-	__stack_chk_guard = 0x000a0dff;
-}
+const unsigned long __stack_chk_guard = 0x000a0dff;
 
 void __stack_chk_fail(void)
 {
···
 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) -

arch/sh/boot/compressed/misc.c

···
 	while(1);	/* Halt */
 }
 
-unsigned long __stack_chk_guard;
-
-void __stack_chk_guard_setup(void)
-{
-	__stack_chk_guard = 0x000a0dff;
-}
+const unsigned long __stack_chk_guard = 0x000a0dff;
 
 void __stack_chk_fail(void)
 {
···
 void decompress_kernel(void)
 {
 	unsigned long output_addr;
-
-	__stack_chk_guard_setup();
 
 #ifdef CONFIG_SUPERH64
 	output_addr = (CONFIG_MEMORY_START + 0x2000);