riscv: 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-v1-2-1df9882bb01a@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/riscv/kernel/kexec_elf.c

@@ -28,7 +28,7 @@ static int riscv_kexec_elf_load(struct kimage *image, struct elfhdr *ehdr,
 	int i;
 	int ret = 0;
 	size_t size;
-	struct kexec_buf kbuf;
+	struct kexec_buf kbuf = {};
 	const struct elf_phdr *phdr;
 
 	kbuf.image = image;
@@ -66,7 +66,7 @@ static int elf_find_pbase(struct kimage *image, unsigned long kernel_len,
 {
 	int i;
 	int ret;
-	struct kexec_buf kbuf;
+	struct kexec_buf kbuf = {};
 	const struct elf_phdr *phdr;
 	unsigned long lowest_paddr = ULONG_MAX;
 	unsigned long lowest_vaddr = ULONG_MAX;

arch/riscv/kernel/kexec_image.c

@@ -41,7 +41,7 @@ static void *image_load(struct kimage *image,
 	struct riscv_image_header *h;
 	u64 flags;
 	bool be_image, be_kernel;
-	struct kexec_buf kbuf;
+	struct kexec_buf kbuf = {};
 	int ret;
 
 	/* Check Image header */

arch/riscv/kernel/machine_kexec_file.c

@@ -261,7 +261,7 @@ int load_extra_segments(struct kimage *image, unsigned long kernel_start,
 	int ret;
 	void *fdt;
 	unsigned long initrd_pbase = 0UL;
-	struct kexec_buf kbuf;
+	struct kexec_buf kbuf = {};
 	char *modified_cmdline = NULL;
 
 	kbuf.image = image;