s390: kexec: initialize kexec_buf struct

The kexec_buf structure was previously declared without initialization.
commit bf454ec ("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/20250827-kbuf_all-v1-3-1df9882bb01a@debian.org
Fixes: bf454ec ("kexec_file: allow to place kexec_buf randomly")
Signed-off-by: Breno Leitao <leitao@debian.org>
Cc: Albert Ou <aou@eecs.berkeley.edu>
Cc: Alexander Gordeev <agordeev@linux.ibm.com>
Cc: Alexandre Ghiti <alex@ghiti.fr>
Cc: Baoquan He <bhe@redhat.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Christian Borntraeger <borntraeger@linux.ibm.com>
Cc: Coiby Xu <coxu@redhat.com>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Palmer Dabbelt <palmer@dabbelt.com>
Cc: Paul Walmsley <paul.walmsley@sifive.com>
Cc: Sven Schnelle <svens@linux.ibm.com>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Will Deacon <will@kernel.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Author: leitao

arch/s390/kernel/kexec_elf.c

@@ -16,7 +16,7 @@
 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

@@ -16,7 +16,7 @@
 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

@@ -129,7 +129,7 @@ static int kexec_file_update_purgatory(struct kimage *image,
 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;
@@ -152,7 +152,7 @@ static int kexec_file_add_purgatory(struct kimage *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;
@@ -184,7 +184,7 @@ static int kexec_file_add_ipl_report(struct kimage *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;