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 <[e-mail]>
Cc: Baoquan He <[e-mail]>
Cc: Vivek Goyal <[e-mail]>
Cc: Dave Young <[e-mail]>
Co-developed-by: Tushar Sugandhi <[e-mail]>
Signed-off-by: Tushar Sugandhi <[e-mail]>
Signed-off-by: Steven Chen <[e-mail]>
Reviewed-by: Stefan Berger <[e-mail]>
Acked-by: Baoquan He <[e-mail]>
Tested-by: Stefan Berger <[e-mail]> # ppc64/kvm
[[e-mail]: Fixed Signed-off-by tag to match author's email ]
Signed-off-by: Mimi Zohar <[e-mail]>

include/linux/kexec.h

···
 
 	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

···
 }
 #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. */
···
 		 * info in purgatory.
 		 */
 		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,

security/integrity/ima/ima_kexec.c

···
 	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");
···
 	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);