ima: kexec: skip IMA segment validation after kexec soft reboot

JIRA: https://issues.redhat.com/browse/RHEL-114162

Upstream Status: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git

commit 9ee8888
Author: Steven Chen <chenste@linux.microsoft.com>
Date:   Mon Apr 21 15:25:10 2025 -0700

    ima: kexec: skip IMA segment validation after kexec soft reboot

    Currently, the function kexec_calculate_store_digests() calculates and
    stores the digest of the segment during the kexec_file_load syscall,
    where the  IMA segment is also allocated.

    Later, the IMA segment will be updated with the measurement log at the
    kexec execute stage when a kexec reboot is initiated. Therefore, the
    digests should be updated for the IMA segment in the  normal case. The
    problem is that the content of memory segments carried over to the new
    kernel during the kexec systemcall can be changed at kexec 'execute'
    stage, but the size and the location of the memory segments cannot be
    changed at kexec 'execute' stage.

    To address this, skip the calculation and storage of the digest for the
    IMA segment in kexec_calculate_store_digests() so that it is not added
    to the purgatory_sha_regions.

    With this change, the IMA segment is not included in the digest
    calculation, storage, and verification.

    Cc: Eric Biederman <ebiederm@xmission.com>
    Cc: Baoquan He <bhe@redhat.com>
    Cc: Vivek Goyal <vgoyal@redhat.com>
    Cc: Dave Young <dyoung@redhat.com>
    Co-developed-by: Tushar Sugandhi <tusharsu@linux.microsoft.com>
    Signed-off-by: Tushar Sugandhi <tusharsu@linux.microsoft.com>
    Signed-off-by: Steven Chen <chenste@linux.microsoft.com>
    Reviewed-by: Stefan Berger <stefanb@linux.ibm.com>
    Acked-by: Baoquan He <bhe@redhat.com>
    Tested-by: Stefan Berger <stefanb@linux.ibm.com> # ppc64/kvm
    [zohar@linux.ibm.com: Fixed Signed-off-by tag to match author's email ]
    Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>

Signed-off-by: Baoquan He <bhe@redhat.com>

Author: Baoquan He

include/linux/kexec.h

@@ -369,6 +369,9 @@ struct kimage {
 
 	phys_addr_t ima_buffer_addr;
 	size_t ima_buffer_size;
+
+	unsigned long ima_segment_index;
+	bool is_ima_segment_index_set;
 #endif
 
 	/* Core ELF header buffer */

kernel/kexec_file.c

@@ -38,6 +38,21 @@ void set_kexec_sig_enforced(void)
 }
 #endif
 
+#ifdef CONFIG_IMA_KEXEC
+static bool check_ima_segment_index(struct kimage *image, int i)
+{
+	if (image->is_ima_segment_index_set && i == image->ima_segment_index)
+		return true;
+	else
+		return false;
+}
+#else
+static bool check_ima_segment_index(struct kimage *image, int i)
+{
+	return false;
+}
+#endif
+
 static int kexec_calculate_store_digests(struct kimage *image);
 
 /* Maximum size in bytes for kernel/initrd files. */
@@ -776,6 +791,13 @@ static int kexec_calculate_store_digests(struct kimage *image)
 		if (ksegment->kbuf == pi->purgatory_buf)
 			continue;
 
+		/*
+		 * Skip the segment if ima_segment_index is set and matches
+		 * the current index
+		 */
+		if (check_ima_segment_index(image, i))
+			continue;
+
 		ret = crypto_shash_update(desc, ksegment->kbuf,
 					  ksegment->bufsz);
 		if (ret)

security/integrity/ima/ima_kexec.c

@@ -145,6 +145,7 @@ void ima_add_kexec_buffer(struct kimage *image)
 	kbuf.buffer = kexec_buffer;
 	kbuf.bufsz = kexec_buffer_size;
 	kbuf.memsz = kexec_segment_size;
+	image->is_ima_segment_index_set = false;
 	ret = kexec_add_buffer(&kbuf);
 	if (ret) {
 		pr_err("Error passing over kexec measurement buffer.\n");
@@ -155,6 +156,8 @@ void ima_add_kexec_buffer(struct kimage *image)
 	image->ima_buffer_addr = kbuf.mem;
 	image->ima_buffer_size = kexec_segment_size;
 	image->ima_buffer = kexec_buffer;
+	image->ima_segment_index = image->nr_segments - 1;
+	image->is_ima_segment_index_set = true;
 
 	kexec_dprintk("kexec measurement buffer for the loaded kernel at 0x%lx.\n",
 		      kbuf.mem);