linux-kernel - Re: [PATCH v5 1/4] kho: add size parameter to kho_add

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Message-ID: <aXhoTWqxIGNglgdV@kernel.org>
Date: Tue, 27 Jan 2026 09:25:01 +0200
From: Mike Rapoport <rppt@...nel.org>
To: Breno Leitao <leitao@...ian.org>
Cc: Alexander Graf <graf@...zon.com>,
	Pasha Tatashin <pasha.tatashin@...een.com>,
	Pratyush Yadav <pratyush@...nel.org>, linux-kernel@...r.kernel.org,
	kexec@...ts.infradead.org, linux-mm@...ck.org,
	usamaarif642@...il.com, rmikey@...a.com, clm@...com,
	riel@...riel.com, SeongJae Park <sj@...nel.org>,
	kernel-team@...a.com
Subject: Re: [PATCH v5 1/4] kho: add size parameter to kho_add_subtree()

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@...nel.org>
> > Signed-off-by: Breno Leitao <leitao@...ian.org>
> 
> Reviewed-by: Mike Rapoport (Microsoft) <rppt@...nel.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.