linux-kernel - [PATCH v26 3/8] kexec: exclude elfcorehdr from the segment digest

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Message-Id: <20230804210359.8321-4-eric.devolder@oracle.com>
Date:   Fri,  4 Aug 2023 17:03:54 -0400
From:   Eric DeVolder <eric.devolder@...cle.com>
To:     linux-kernel@...r.kernel.org, david@...hat.com, osalvador@...e.de,
        corbet@....net, tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
        dave.hansen@...ux.intel.com, x86@...nel.org, bhe@...hat.com,
        ebiederm@...ssion.com, kexec@...ts.infradead.org
Cc:     hpa@...or.com, gregkh@...uxfoundation.org, rafael@...nel.org,
        vgoyal@...hat.com, dyoung@...hat.com, lf32.dev@...il.com,
        akpm@...ux-foundation.org, naveen.n.rao@...ux.vnet.ibm.com,
        zohar@...ux.ibm.com, bhelgaas@...gle.com, vbabka@...e.cz,
        tiwai@...e.de, seanjc@...gle.com, linux@...ssschuh.net,
        vschneid@...hat.com, linux-mm@...ck.org, linux-doc@...r.kernel.org,
        sourabhjain@...ux.ibm.com, konrad.wilk@...cle.com,
        boris.ostrovsky@...cle.com, eric.devolder@...cle.com
Subject: [PATCH v26 3/8] kexec: exclude elfcorehdr from the segment digest

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. The digest is embedded into
the purgatory image prior to placing in memory.

Updates to the elfcorehdr in response to CPU and memory changes
would cause the purgatory integrity checking to fail (at crash time,
and no vmcore created). Therefore, the elfcorehdr segment is
explicitly excluded from the purgatory digest, enabling updates to
the elfcorehdr while also avoiding the need to recompute the hash
digest and reload purgatory.

Suggested-by: Baoquan He <bhe@...hat.com>
Signed-off-by: Eric DeVolder <eric.devolder@...cle.com>
Reviewed-by: Sourabh Jain <sourabhjain@...ux.ibm.com>
Acked-by: Hari Bathini <hbathini@...ux.ibm.com>
Acked-by: Baoquan He <bhe@...hat.com>
---
 kernel/kexec_file.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/kernel/kexec_file.c b/kernel/kexec_file.c
index 453b7a513540..e2ec9d7b9a1f 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