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: <CA+CK2bB=k6ZxeEuLC9Xwtzmgm5MZdpH2sRgk84WQVm4uoeHsVw@mail.gmail.com>
Date: Wed, 29 Oct 2025 18:22:46 -0400
From: Pasha Tatashin <pasha.tatashin@...een.com>
To: Mike Rapoport <rppt@...nel.org>
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 Andrew,

Would you like me to resend the series with the "+       depends on
KEXEC_HANDOVER" fix from Mike, or would you apply it into your tree
directly?

Thank you,
Pasha

On Wed, Oct 29, 2025 at 4:48 AM Mike Rapoport <rppt@...nel.org> wrote:
>
> 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.