LoongArch: kexec: Initialize the kexec_buf structure

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 is
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.

Fixes: bf454ec31add ("kexec_file: allow to place kexec_buf randomly")
Link: https://lore.kernel.org/r/20250827-kbuf_all-v1-2-1df9882bb01a@debian.org
Signed-off-by: Youling Tang <tangyouling@kylinos.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>
Signed-off-by: maoxiaochuan <maoxiaochuan@loongson.cn>

arch/loongarch/kernel/kexec_efi.c

@@ -42,7 +42,7 @@ static void *efi_kexec_load(struct kimage *image,
 {
 	int ret;
 	unsigned long text_offset, kernel_segment_number;
-	struct kexec_buf kbuf;
+	struct kexec_buf kbuf = {};
 	struct kexec_segment *kernel_segment;
 	struct loongarch_image_header *h;
 

arch/loongarch/kernel/kexec_elf.c

@@ -59,7 +59,7 @@ static void *elf_kexec_load(struct kimage *image,
 	int ret;
 	unsigned long text_offset, kernel_segment_number;
 	struct elfhdr ehdr;
-	struct kexec_buf kbuf;
+	struct kexec_buf kbuf = {};
 	struct kexec_elf_info elf_info;
 	struct kexec_segment *kernel_segment;
 

arch/loongarch/kernel/machine_kexec_file.c

@@ -143,7 +143,7 @@ int load_other_segments(struct kimage *image,
 	unsigned long initrd_load_addr = 0;
 	unsigned long orig_segments = image->nr_segments;
 	char *modified_cmdline = NULL;
-	struct kexec_buf kbuf;
+	struct kexec_buf kbuf = {};
 
 	kbuf.image = image;
 	/* Don't allocate anything below the kernel */