Re: [PATCH v5 1/4] kho: add size parameter to kho_add_subtree()

Mike Rapoport
2026-01-27T07:23:45Z

On Mon, Jan 26, 2026 at 08:07:23AM -0800, Breno Leitao wrote:
> kho_add_subtree() assumes the fdt argument is always an FDT and calls
> fdt_totalsize() on it in the debugfs code path. This assumption will
> break if a caller passes arbitrary data instead of an FDT.
>
> When CONFIG_KEXEC_HANDOVER_DEBUGFS is enabled, kho_debugfs_fdt_add()
> calls __kho_debugfs_fdt_add(), which executes:
>
> f->wrapper.size = fdt_totalsize(fdt);
>
> Fix this by adding an explicit size parameter to kho_add_subtree() so
> callers specify the blob size. This allows subtrees to contain
> arbitrary data formats, not just FDTs. Update all callers:
>
> - memblock.c: use fdt_totalsize(fdt)
> - luo_core.c: use fdt_totalsize(fdt_out)
> - test_kho.c: use fdt_totalsize()
> - kexec_handover.c (root fdt): use fdt_totalsize(kho_out.fdt)
>
> Also update kho_in_debugfs_init() to compute sizes using fdt_totalsize()
> for the root and sub-FDTs it processes, since these are known to be
> actual FDT blobs.
>
> Suggested-by: Pratyush Yadav <pratyush@kernel.org>
> Signed-off-by: Breno Leitao <leitao@debian.org>

Reviewed-by: Mike Rapoport (Microsoft) <rppt@kernel.org>

> ---
> include/linux/kexec_handover.h | 4 ++--
> kernel/liveupdate/kexec_handover.c | 8 +++++---
> kernel/liveupdate/kexec_handover_debugfs.c | 15 +++++++++------
> kernel/liveupdate/kexec_handover_internal.h | 5 +++--
> kernel/liveupdate/luo_core.c | 3 ++-
> lib/test_kho.c | 3 ++-
> mm/memblock.c | 2 +-
> 7 files changed, 24 insertions(+), 16 deletions(-)
>
> diff --git a/include/linux/kexec_handover.h b/include/linux/kexec_handover.h
> index ac4129d1d7416..abb1d324f42d0 100644
> --- a/include/linux/kexec_handover.h
> +++ b/include/linux/kexec_handover.h
> @@ -32,7 +32,7 @@ void kho_restore_free(void *mem);
> struct folio *kho_restore_folio(phys_addr_t phys);
> struct page *kho_restore_pages(phys_addr_t phys, unsigned long nr_pages);
> void *kho_restore_vmalloc(const struct kho_vmalloc *preservation);
> -int kho_add_subtree(const char *name, void *fdt);
> +int kho_add_subtree(const char *name, void *fdt, size_t size);

I'd rename 'void *fdt' to 'void *blob' to make it clearer that subtree isn't
necessary an FDT.
And s/fdt/blob/ in debugfs function names.
All this could be a separate cleanup.

--
Sincerely yours,
Mike.