linux-kernel - Re: [PATCH v4 07/10] crash hp: exclude elfcorehdr from the segment digest

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Date:   Wed, 23 Feb 2022 12:00:57 +0800
From:   Baoquan He <bhe@...hat.com>
To:     Eric DeVolder <eric.devolder@...cle.com>
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org,
        kexec@...ts.infradead.org, ebiederm@...ssion.com,
        dyoung@...hat.com, vgoyal@...hat.com, tglx@...utronix.de,
        mingo@...hat.com, bp@...en8.de, dave.hansen@...ux.intel.com,
        hpa@...or.com, nramas@...ux.microsoft.com, thomas.lendacky@....com,
        robh@...nel.org, efault@....de, rppt@...nel.org,
        konrad.wilk@...cle.com, boris.ostrovsky@...cle.com
Subject: Re: [PATCH v4 07/10] crash hp: exclude elfcorehdr from the segment
 digest

On 02/09/22 at 02:57pm, Eric DeVolder wrote:
> When a crash kernel is loaded via the kexec_file_load syscall, the
> kernel places the various segments (ie crash kernel, crash initrd,
> boot_params, elfcorehdr, purgatory, etc) in memory. For those
> architectures that utilize purgatory, a hash digest of the segments
> is calculated for integrity checking. This digest is embedded into
> the purgatory image prior to placing purgatory in memory.
> 
> Since hotplug events cause changes to the elfcorehdr, purgatory
> integrity checking fails (at crash time, and no kdump created).
> As a result, this change explicitly excludes the elfcorehdr segment
> from the list of segments used to create the digest. By doing so,
> this permits changes to the elfcorehdr in response to hotplug events,
> without having to also reload purgatory due to the change to the
> digest.

Acked-by: Baoquan He <bhe@...hat.com>

> 
> Signed-off-by: Eric DeVolder <eric.devolder@...cle.com>
> ---
>  kernel/kexec_file.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/kernel/kexec_file.c b/kernel/kexec_file.c
> index 801d0d0a5012..93bb0c0ce66c 100644
> --- a/kernel/kexec_file.c
> +++ b/kernel/kexec_file.c
> @@ -765,6 +765,12 @@ static int kexec_calculate_store_digests(struct kimage *image)
>  	for (j = i = 0; i < image->nr_segments; i++) {
>  		struct kexec_segment *ksegment;
>  
> +#ifdef CONFIG_CRASH_HOTPLUG
> +		/* This segment excluded to allow future changes via hotplug */
> +		if (image->elf_index_valid && (j == image->elf_index))
> +			continue;
> +#endif
> +
>  		ksegment = &image->segment[i];
>  		/*
>  		 * Skip purgatory as it will be modified once we put digest
> -- 
> 2.27.0
>