Re: [PATCH v2] kho: validate preserved memory map during population

[Mike Rapoport <rppt@kernel.org>]

On Thu, Dec 18, 2025 at 10:08:54PM -0500, Pasha Tatashin wrote:
> If the previous kernel enabled KHO but did not call kho_finalize()
> (e.g., CONFIG_LIVEUPDATE=n or userspace skipped the finalization step),
> the 'preserved-memory-map' property in the FDT remains empty/zero.
> 
> Previously, kho_populate() would succeed regardless of the memory map's
> state, reserving the incoming scratch regions in memblock. However,
> kho_memory_init() would later fail to deserialize the empty map. By that
> time, the scratch regions were already registered, leading to partial
> initialization and subsequent list corruption (double-free) during
> kho_init().
> 
> Move the validation of the preserved memory map earlier into
> kho_populate(). If the memory map is empty/NULL:
> 1. Abort kho_populate() immediately with -ENOENT.
> 2. Do not register or reserve the incoming scratch memory, allowing the new
>    kernel to reclaim those pages as standard free memory.
> 3. Leave the global 'kho_in' state uninitialized.
> 
> Consequently, kho_memory_init() sees no active KHO context
> (kho_in.mem_chunks_phys is 0) and falls back to kho_reserve_scratch(),
> allocating fresh scratch memory as if it were a standard cold boot.
> 
> Fixes: de51999e687c ("kho: allow memory preservation state updates after finalization")
> Reported-by: Ricardo <ricardo@example.com>

I believe Ricardo has a real email ;-)

> Closes: https://lore.kernel.org/all/20251218215613.GA17304@ranerica-svr.sc.intel.com
> Signed-off-by: Pasha Tatashin <pasha.tatashin@soleen.com>
> ---
> Changes v2:
> - Removed phys_to_virt() from kho_populate().
> 
>  kernel/liveupdate/kexec_handover.c | 39 ++++++++++++++++--------------
>  1 file changed, 21 insertions(+), 18 deletions(-)
> 
> diff --git a/kernel/liveupdate/kexec_handover.c b/kernel/liveupdate/kexec_handover.c
> index 9dc51fab604f..6ba554208c81 100644
> --- a/kernel/liveupdate/kexec_handover.c
> +++ b/kernel/liveupdate/kexec_handover.c
> @@ -460,27 +460,23 @@ static void __init deserialize_bitmap(unsigned int order,
>  	}
>  }
>  
> -/* Return true if memory was deserizlied */
> -static bool __init kho_mem_deserialize(const void *fdt)
> +/* Returns head of preserved physical memory chunks pointer from FDT */
> +static phys_addr_t __init kho_get_mem_chunks_phys(const void *fdt)

Let's s/mem_chunks/mem_map/ everywhere please.
And the comment would become

/* Returns physical address of the preserved memory map from FDT */

Other than that

Reviewed-by: Mike Rapoport (Microsoft) <rppt@kernel.org>

-- 
Sincerely yours,
Mike.