arm64: kernel: initialize missing kexec_buf->random field

Commit bf454ec31a ("kexec_file: allow to place kexec_buf randomly")
introduced the kexec_buf->random field to enable random placement of
kexec_buf.

However, this field was never properly initialized for kexec images
that do not need to be placed randomly, leading to the following UBSAN
warning:

[  +0.364528] ------------[ cut here ]------------
[  +0.000019] UBSAN: invalid-load in ./include/linux/kexec.h:210:12
[  +0.000131] load of value 2 is not a valid value for type 'bool' (aka '_Bool')
[  +0.000003] CPU: 4 UID: 0 PID: 927 Comm: kexec Not tainted 6.18.0-rc7+ #3 PREEMPT(full)
[  +0.000002] Hardware name: QEMU QEMU Virtual Machine, BIOS 0.0.0 02/06/2015
[  +0.000000] Call trace:
[  +0.000001]  show_stack+0x24/0x40 (C)
[  +0.000006]  __dump_stack+0x28/0x48
[  +0.000002]  dump_stack_lvl+0x7c/0xb0
[  +0.000002]  dump_stack+0x18/0x34
[  +0.000001]  ubsan_epilogue+0x10/0x50
[  +0.000002]  __ubsan_handle_load_invalid_value+0xc8/0xd0
[  +0.000003]  locate_mem_hole_callback+0x28c/0x2a0
[  +0.000003]  kexec_locate_mem_hole+0xf4/0x2f0
[  +0.000001]  kexec_add_buffer+0xa8/0x178
[  +0.000002]  image_load+0xf0/0x258
[  +0.000001]  __arm64_sys_kexec_file_load+0x510/0x718
[  +0.000002]  invoke_syscall+0x68/0xe8
[  +0.000001]  el0_svc_common+0xb0/0xf8
[  +0.000002]  do_el0_svc+0x28/0x48
[  +0.000001]  el0_svc+0x40/0xe8
[  +0.000002]  el0t_64_sync_handler+0x84/0x140
[  +0.000002]  el0t_64_sync+0x1bc/0x1c0

To address this, initialise kexec_buf->random field properly.

Fixes: bf454ec31a ("kexec_file: allow to place kexec_buf randomly")
Suggested-by: Breno Leitao <leitao@debian.org>
Cc: stable@vger.kernel.org
Signed-off-by: Yeoreum Yun <yeoreum.yun@arm.com>
Reviewed-by: Breno Leitao <leitao@debian.org>
Link: https://lore.kernel.org/all/oninomspajhxp4omtdapxnckxydbk2nzmrix7rggmpukpnzadw@c67o7njgdgm3/ [1]
Link: https://lore.kernel.org/all/20250825180531.94bfb86a26a43127c0a1296f@linux-foundation.org/ [2]
Link: https://lkml.kernel.org/r/20250826-akpm-v1-1-3c831f0e3799@debian.org
Signed-off-by: Breno Leitao <leitao@debian.org>
Suggested-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Pratyush Yadav <pratyush@kernel.org>
Signed-off-by: Will Deacon <will@kernel.org>

arch/arm64/kernel/kexec_image.c

@@ -41,7 +41,7 @@ static void *image_load(struct kimage *image,
 	struct arm64_image_header *h;
 	u64 flags, value;
 	bool be_image, be_kernel;
-	struct kexec_buf kbuf;
+	struct kexec_buf kbuf = {};
 	unsigned long text_offset, kernel_segment_number;
 	struct kexec_segment *kernel_segment;
 	int ret;