From:   Eric DeVolder <eric.devolder@oracle.com>
To:     linux-kernel@vger.kernel.org, x86@kernel.org,
        kexec@lists.infradead.org, ebiederm@xmission.com,
        dyoung@redhat.com, bhe@redhat.com, vgoyal@redhat.com
Cc:     tglx@linutronix.de, mingo@redhat.com, bp@alien8.de,
        dave.hansen@linux.intel.com, hpa@zytor.com,
        nramas@linux.microsoft.com, thomas.lendacky@amd.com,
        robh@kernel.org, efault@gmx.de, rppt@kernel.org, david@redhat.com,
        sourabhjain@linux.ibm.com, konrad.wilk@oracle.com,
        boris.ostrovsky@oracle.com, eric.devolder@oracle.com
Subject: [PATCH v20 3/8] kexec: exclude elfcorehdr from the segment digest
Date:   Fri, 17 Mar 2023 17:21:24 -0400
Message-Id: <20230317212128.21424-4-eric.devolder@oracle.com>
In-Reply-To: <20230317212128.21424-1-eric.devolder@oracle.com>
References: <20230317212128.21424-1-eric.devolder@oracle.com>
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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.

This patchset updates the elfcorehdr on CPU or memory changes.
However, changes to the elfcorehdr in turn cause purgatory
integrity checking to fail (at crash time, and no vmcore created).
Therefore, this patch explicitly excludes the elfcorehdr segment
from the list of segments used to create the digest. By doing so,
this permits updates to the elfcorehdr in response to CPU or memory
changes, and avoids the need to also recompute the hash digest and
reload purgatory.

Signed-off-by: Eric DeVolder <eric.devolder@oracle.com>
Reviewed-by: Sourabh Jain <sourabhjain@linux.ibm.com>
Acked-by: Baoquan He <bhe@redhat.com>
---
 kernel/kexec_file.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/kernel/kexec_file.c b/kernel/kexec_file.c
index 0b560064579e..a28f01318a47 100644
--- a/kernel/kexec_file.c
+++ b/kernel/kexec_file.c
@@ -726,6 +726,12 @@ 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
+		/* Exclude elfcorehdr segment to allow future changes via hotplug */
+		if (j == image->elfcorehdr_index)
+			continue;
+#endif
+
 		ksegment = &image->segment[i];
 		/*
 		 * Skip purgatory as it will be modified once we put digest
-- 
2.31.1