Re: [PATCH] arm64: kexec: Initialize kexec_buf struct in image_load()

On Tue, Aug 26, 2025 at 05:08:51AM -0700, Breno Leitao wrote:

The kexec_buf structure was previously declared without initialization
in image_load(). This led to a UBSAN warning when the structure was
expanded and uninitialized fields were accessed [1].

Just to check my understanding, is that only a problem for new fields
(e.g. the 'random' field added in [1]), or do we have UBSAN warnigns for
any existing fields? I assume there's no problem with existing fields
today.

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

Andrew Morton suggested that this function is only called 3x a week[2],
thus, the memset() cost is inexpressive.

Link: https://lore.kernel.org/all/oninomspajhxp4omtdapxnckxydbk2nzmrix7rggmpukpnzadw@c67o7njgdgm3/ (local) [1]
Link: https://lore.kernel.org/all/20250825180531.94bfb86a26a43127c0a1296f@linux-foundation.org/ (local) [2]
Suggested-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Breno Leitao <leitao@debian.org>

This looks fine to me, but I reckon it should be added to the series
which extends kexec_buf, unless there's some reason to avoid that?

---
 arch/arm64/kernel/kexec_image.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

IIUC arch/arm64/kernel/machine_kexec_file.c would need the same
treatment in load_other_segments().

If other architectures need this, it'd probably make sense to clean that
up treewide in one go. It looks like at least riscv and s390 need that
from a quick grep:

| [mark@lakrids:~/src/linux]% git grep -w 'struct kexec_buf .*;'
| arch/arm64/kernel/kexec_image.c:        struct kexec_buf kbuf;
| arch/arm64/kernel/machine_kexec_file.c: struct kexec_buf kbuf;
| arch/powerpc/include/asm/kexec.h:int arch_kexec_locate_mem_hole(struct kexec_buf *kbuf);
| arch/powerpc/include/asm/kexec.h:                                 struct kexec_buf *kbuf);
| arch/riscv/kernel/elf_kexec.c:  struct kexec_buf kbuf;
| arch/riscv/kernel/elf_kexec.c:  struct kexec_buf kbuf;
| arch/riscv/kernel/elf_kexec.c:  struct kexec_buf kbuf;
| arch/s390/kernel/kexec_elf.c:   struct kexec_buf buf;
| arch/s390/kernel/kexec_image.c: struct kexec_buf buf;
| arch/s390/kernel/machine_kexec_file.c:  struct kexec_buf buf;
| arch/s390/kernel/machine_kexec_file.c:  struct kexec_buf buf;
| arch/s390/kernel/machine_kexec_file.c:  struct kexec_buf buf;
| include/linux/kexec.h:int kexec_load_purgatory(struct kimage *image, struct kexec_buf *kbuf);
| include/linux/kexec.h:extern int kexec_add_buffer(struct kexec_buf *kbuf);
| include/linux/kexec.h:int kexec_locate_mem_hole(struct kexec_buf *kbuf);
| kernel/kexec_file.c:    struct kexec_buf *kbuf = (struct kexec_buf *)arg;

Mark.