[PATCH v13 4/7] kexec: exclude elfcorehdr from the segment digest

[Eric DeVolder]

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.

Signed-off-by: Eric DeVolder <eric.devolder at oracle.com>
Acked-by: Baoquan He <bhe at 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 f98d1742872b..4d3451cf9f0c 100644
--- a/kernel/kexec_file.c
+++ b/kernel/kexec_file.c
@@ -723,6 +723,12 @@ static int kexec_calculate_store_digests(struct kimage *image)
 	for (j = i = 0; i < image->nr_segments; i++) {
 		struct kexec_segment *ksegment;
 
+		if (IS_ENABLED(CONFIG_HOTPLUG_CPU) || IS_ENABLED(CONFIG_MEMORY_HOTPLUG)) {
+			/* Exclude elfcorehdr segment to allow future changes via hotplug */
+			if (image->elfcorehdr_index_valid && (j == image->elfcorehdr_index))
+				continue;
+		}
+
 		ksegment = &image->segment[i];
 		/*
 		 * Skip purgatory as it will be modified once we put digest
-- 
2.31.1