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

Mike Rapoport
2026-01-27T07:25:16Z

On Tue, Jan 27, 2026 at 09:23:38AM +0200, Mike Rapoport wrote:
> 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.

Scratch that, I didn't look at the second patch :)

> And s/fdt/blob/ in debugfs function names.
> All this could be a separate cleanup.
>
>
> --
> Sincerely yours,
> Mike.

--
Sincerely yours,
Mike.