linux-kernel - Re: [PATCH 0/3] arm64: kdump : take off the protection on crashkernel memory region

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Date:   Sat, 25 Mar 2023 11:00:11 +0800
From:   Baoquan He <bhe@...hat.com>
To:     "Leizhen (ThunderTown)" <thunder.leizhen@...wei.com>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        linux-kernel@...r.kernel.org, horms@...nel.org,
        John.p.donnelly@...cle.com, will@...nel.org,
        kexec@...ts.infradead.org, ardb@...nel.org, rppt@...nel.org,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 0/3] arm64: kdump : take off the protection on
 crashkernel memory region

On 03/25/23 at 10:14am, Leizhen (ThunderTown) wrote:
> 
> 
> On 2023/3/25 1:11, Catalin Marinas wrote:
> > On Fri, Mar 24, 2023 at 09:18:35PM +0800, Baoquan He wrote:
> >> Baoquan He (3):
> >>   arm64: kdump : take off the protection on crashkernel memory region
> >>   arm64: kdump: do not map crashkernel region specifically
> >>   arm64: kdump: defer the crashkernel reservation for platforms with no
> >>     DMA memory zones
> >>
> >>  arch/arm64/include/asm/kexec.h    |  6 -----
> >>  arch/arm64/include/asm/memory.h   |  5 ----
> >>  arch/arm64/kernel/machine_kexec.c | 20 --------------
> >>  arch/arm64/mm/init.c              |  6 +----
> >>  arch/arm64/mm/mmu.c               | 43 -------------------------------
> >>  5 files changed, 1 insertion(+), 79 deletions(-)
> > 
> > This series works for me and it has a negative diffstat as well (though
> > I'm sure people will try to bring it back ;)).
> 
> After the write protection is removed, it is recommended that crc32 check
> be added. However, it can be added later.

That's a great catch. We have calculated the checusum with sha256 in
user space and kernel, and verify it in purgatory in user space.
However, arm64 seems to not do the verifying in kernel if
kexec_file_load is used. Please see kexec_calculate_store_digests().

If stamping happened, the checksum verification can help us spot it.
Yes, this can be added later. Thanks for raising that.