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

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Message-ID: <aXhn8ieKtj3T3FCc@kernel.org>
Date: Tue, 27 Jan 2026 09:23:30 +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 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.
And s/fdt/blob/ in debugfs function names.
All this could be a separate cleanup.


-- 
Sincerely yours,
Mike.