linux-kernel - Re: [PATCH v3 1/3] liveupdate: kho: warn and fail on metadata or preserved memory in scratch area

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Message-ID: <aQHUyyFtiNZhx8jo@kernel.org>
Date: Wed, 29 Oct 2025 10:48:11 +0200
From: Mike Rapoport <rppt@...nel.org>
To: Pasha Tatashin <pasha.tatashin@...een.com>
Cc: akpm@...ux-foundation.org, brauner@...nel.org, corbet@....net,
	graf@...zon.com, jgg@...pe.ca, linux-kernel@...r.kernel.org,
	linux-kselftest@...r.kernel.org, linux-mm@...ck.org,
	masahiroy@...nel.org, ojeda@...nel.org, pratyush@...nel.org,
	rdunlap@...radead.org, tj@...nel.org, jasonmiu@...gle.com,
	dmatlack@...gle.com, skhawaja@...gle.com
Subject: Re: [PATCH v3 1/3] liveupdate: kho: warn and fail on metadata or
 preserved memory in scratch area

Hi Pasha,

On Mon, Oct 20, 2025 at 08:08:50PM -0400, Pasha Tatashin wrote:
> It is invalid for KHO metadata or preserved memory regions to be located
> within the KHO scratch area, as this area is overwritten when the next
> kernel is loaded, and used early in boot by the next kernel. This can
> lead to memory corruption.
> 
> Adds checks to kho_preserve_* and KHO's internal metadata allocators
> (xa_load_or_alloc, new_chunk) to verify that the physical address of the
> memory does not overlap with any defined scratch region. If an overlap
> is detected, the operation will fail and a WARN_ON is triggered. To
> avoid performance overhead in production kernels, these checks are
> enabled only when CONFIG_KEXEC_HANDOVER_DEBUG is selected.
> 
> Signed-off-by: Pasha Tatashin <pasha.tatashin@...een.com>
> ---
>  kernel/Kconfig.kexec             |  9 ++++++
>  kernel/Makefile                  |  1 +
>  kernel/kexec_handover.c          | 53 ++++++++++++++++++++++----------
>  kernel/kexec_handover_debug.c    | 25 +++++++++++++++
>  kernel/kexec_handover_internal.h | 16 ++++++++++
>  5 files changed, 87 insertions(+), 17 deletions(-)
>  create mode 100644 kernel/kexec_handover_debug.c
>  create mode 100644 kernel/kexec_handover_internal.h
> 
> diff --git a/kernel/Kconfig.kexec b/kernel/Kconfig.kexec
> index 422270d64820..c94d36b5fcd9 100644
> --- a/kernel/Kconfig.kexec
> +++ b/kernel/Kconfig.kexec
> @@ -109,6 +109,15 @@ config KEXEC_HANDOVER
>  	  to keep data or state alive across the kexec. For this to work,
>  	  both source and target kernels need to have this option enabled.
>  
> +config KEXEC_HANDOVER_DEBUG
> +	bool "Enable Kexec Handover debug checks"
> +	depends on KEXEC_HANDOVER_DEBUGFS

I missed that in the earlier review, should be "depends on KEXEC_HANDOVER"

@Andrew, can you please fold this into what's now commit 0e0faeffd144
("kho: warn and fail on metadata or preserved memory in scratch area")

diff --git a/kernel/Kconfig.kexec b/kernel/Kconfig.kexec
index c94d36b5fcd9..54e581072617 100644
--- a/kernel/Kconfig.kexec
+++ b/kernel/Kconfig.kexec
@@ -111,7 +111,7 @@ config KEXEC_HANDOVER
 
 config KEXEC_HANDOVER_DEBUG
 	bool "Enable Kexec Handover debug checks"
-	depends on KEXEC_HANDOVER_DEBUGFS
+	depends on KEXEC_HANDOVER
 	help
 	  This option enables extra sanity checks for the Kexec Handover
 	  subsystem. Since, KHO performance is crucial in live update

> +	help
> +	  This option enables extra sanity checks for the Kexec Handover
> +	  subsystem. Since, KHO performance is crucial in live update
> +	  scenarios and the extra code might be adding overhead it is
> +	  only optionally enabled.
> +
>  config CRASH_DUMP
>  	bool "kernel crash dumps"
>  	default ARCH_DEFAULT_CRASH_DUMP

-- 
Sincerely yours,
Mike.