[PATCH] kho: make sure folio being restored is actually from KHO

[Mike Rapoport]

On Wed, Sep 10, 2025 at 05:34:40PM +0200, Pratyush Yadav wrote:
> When restoring a folio using kho_restore_folio(), no sanity checks are
> done to make sure the folio actually came from a kexec handover. The
> caller is trusted to pass in the right address. If the caller has a bug
> and passes in a wrong address, an in-use folio might be "restored" and
> returned, causing all sorts of memory corruption.
> 
> Harden the folio restore logic by stashing in a magic number in
> page->private along with the folio order. If the magic number does not
> match, the folio won't be touched. page->private is an unsigned long.
> The union kho_page_info splits it into two parts, with one holding the
> order and the other holding the magic number.

I think the sanity checks belongs to the core kho_restore_page() function
and kho_restore_folio() should be a thin wrapper for that, at least until
we'd need to allocate struct folio there.
 
> Signed-off-by: Pratyush Yadav <pratyush at kernel.org>
> ---
>  kernel/kexec_handover.c | 29 ++++++++++++++++++++++++-----
>  1 file changed, 24 insertions(+), 5 deletions(-)

-- 
Sincerely yours,
Mike.