s390: kexec: initialize kexec_buf struct

The kexec_buf structure was previously declared without initialization.
commit bf454ec31add ("kexec_file: allow to place kexec_buf randomly")
added a field that is always read but not consistently populated by all
architectures. This un-initialized field will contain garbage.

This is also triggering a UBSAN warning when the uninitialized data was
accessed:

------------[ cut here ]------------
UBSAN: invalid-load in ./include/linux/kexec.h:210:10
load of value 252 is not a valid value for type '_Bool'

Zero-initializing kexec_buf at declaration ensures all fields are
cleanly set, preventing future instances of uninitialized memory being
used.

Link: https://lkml.kernel.org/r/[e-mail]
Fixes: bf454ec31add ("kexec_file: allow to place kexec_buf randomly")
Signed-off-by: Breno Leitao <[e-mail]>
Cc: Albert Ou <[e-mail]>
Cc: Alexander Gordeev <[e-mail]>
Cc: Alexandre Ghiti <[e-mail]>
Cc: Baoquan He <[e-mail]>
Cc: Catalin Marinas <[e-mail]>
Cc: Christian Borntraeger <[e-mail]>
Cc: Coiby Xu <[e-mail]>
Cc: Heiko Carstens <[e-mail]>
Cc: Palmer Dabbelt <[e-mail]>
Cc: Paul Walmsley <[e-mail]>
Cc: Sven Schnelle <[e-mail]>
Cc: Vasily Gorbik <[e-mail]>
Cc: Will Deacon <[e-mail]>
Cc: <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>

arch/s390/kernel/kexec_elf.c

···
 static int kexec_file_add_kernel_elf(struct kimage *image,
 				     struct s390_load_data *data)
 {
-	struct kexec_buf buf;
+	struct kexec_buf buf = {};
 	const Elf_Ehdr *ehdr;
 	const Elf_Phdr *phdr;
 	Elf_Addr entry;

arch/s390/kernel/kexec_image.c

···
 static int kexec_file_add_kernel_image(struct kimage *image,
 				       struct s390_load_data *data)
 {
-	struct kexec_buf buf;
+	struct kexec_buf buf = {};
 
 	buf.image = image;
 

arch/s390/kernel/machine_kexec_file.c

···
 static int kexec_file_add_purgatory(struct kimage *image,
 				    struct s390_load_data *data)
 {
-	struct kexec_buf buf;
+	struct kexec_buf buf = {};
 	int ret;
 
 	buf.image = image;
···
 static int kexec_file_add_initrd(struct kimage *image,
 				 struct s390_load_data *data)
 {
-	struct kexec_buf buf;
+	struct kexec_buf buf = {};
 	int ret;
 
 	buf.image = image;
···
 {
 	__u32 *lc_ipl_parmblock_ptr;
 	unsigned int len, ncerts;
-	struct kexec_buf buf;
+	struct kexec_buf buf = {};
 	unsigned long addr;
 	void *ptr, *end;
 	int ret;