linux-kernel - Re: [PATCH v3 0/3] KHO: kfence + KHO memory corruption fix

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Message-ID: <aPchmxfh4ACM0vY2@kernel.org>
Date: Tue, 21 Oct 2025 09:00:59 +0300
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 0/3] KHO: kfence + KHO memory corruption fix

On Mon, Oct 20, 2025 at 08:08:49PM -0400, Pasha Tatashin wrote:
> This series fixes a memory corruption bug in KHO that occurs when KFENCE
> is enabled.
> 
> The root cause is that KHO metadata, allocated via kzalloc(), can be
> randomly serviced by kfence_alloc(). When a kernel boots via KHO, the
> early memblock allocator is restricted to a "scratch area". This forces
> the KFENCE pool to be allocated within this scratch area, creating a
> conflict. If KHO metadata is subsequently placed in this pool, it gets
> corrupted during the next kexec operation.
> 
> Patch 1/3 introduces a debug-only feature (CONFIG_KEXEC_HANDOVER_DEBUG)
> that adds checks to detect and fail any operation that attempts to place
> KHO metadata or preserved memory within the scratch area. This serves as
> a validation and diagnostic tool to confirm the problem without
> affecting production builds.
> 
> Patch 2/3 Increases bitmap to PAGE_SIZE, so buddy allocator can be used.
> 
> Patch 3/3 Provides the fix by modifying KHO to allocate its metadata
> directly from the buddy allocator instead of slab. This bypasses the
> KFENCE interception entirely.
> 
> Pasha Tatashin (3):
>   liveupdate: kho: warn and fail on metadata or preserved memory in
>     scratch area
>   liveupdate: kho: Increase metadata bitmap size to PAGE_SIZE
>   liveupdate: kho: allocate metadata directly from the buddy allocator

With liveupdate: dropped from the subjects

Reviewed-by: Mike Rapoport (Microsoft) <rppt@...nel.org>
 
>  include/linux/gfp.h              |  3 ++
>  kernel/Kconfig.kexec             |  9 ++++
>  kernel/Makefile                  |  1 +
>  kernel/kexec_handover.c          | 72 ++++++++++++++++++++------------
>  kernel/kexec_handover_debug.c    | 25 +++++++++++
>  kernel/kexec_handover_internal.h | 16 +++++++
>  6 files changed, 100 insertions(+), 26 deletions(-)
>  create mode 100644 kernel/kexec_handover_debug.c
>  create mode 100644 kernel/kexec_handover_internal.h
> 
> 
> base-commit: 6548d364a3e850326831799d7e3ea2d7bb97ba08
> -- 
> 2.51.0.869.ge66316f041-goog
> 

-- 
Sincerely yours,
Mike.