linux-kernel - Re: [PATCH v3] kho: validate preserved memory map during population

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Message-ID: <20251219132731.GA18378@ranerica-svr.sc.intel.com>
Date: Fri, 19 Dec 2025 05:27:31 -0800
From: Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
To: Pasha Tatashin <pasha.tatashin@...een.com>
Cc: akpm@...ux-foundation.org, rppt@...nel.org, graf@...zon.com,
	linux-kernel@...r.kernel.org, kexec@...ts.infradead.org,
	linux-mm@...ck.org, pratyush@...nel.org
Subject: Re: [PATCH v3] kho: validate preserved memory map during population

On Fri, Dec 19, 2025 at 02:12:09AM -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 Neri <ricardo.neri-calderon@...ux.intel.com>
> Closes: https://lore.kernel.org/all/20251218215613.GA17304@ranerica-svr.sc.intel.com
> Signed-off-by: Pasha Tatashin <pasha.tatashin@...een.com>
> Reviewed-by: Mike Rapoport (Microsoft) <rppt@...nel.org>

Thanks for the patch (and fixing my e-mail ;)). This fixes the reported
issue and now I can kexec reboot correctly with an empty, unfinalized KHO
FDT.

Tested-by: Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>