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

[Pratyush Yadav]

On Tue, Sep 16 2025, Mike Rapoport wrote:

> 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.

Hmm, okay. I can do that for the next version.

-- 
Regards,
Pratyush Yadav