[PATCH v4 4/7] crash_dump: reuse saved dm crypt keys for CPU/memory hot-plugging

[Coiby Xu <coxu@redhat.com>]

When there is CPU/memory hot-plugging, the kdump kernel image and initrd
will be reloaded. The user space can write the "reuse" command to
/sys/kernel/crash_dm_crypt_key so the stored keys can be re-saved again.

Note currently only x86 (commit ea53ad9cf73b ("x86/crash: add x86 crash
hotplug support")) and ppc (WIP) supports the new infrastructure
(commit 247262756121 ("crash: add generic infrastructure for crash
hotplug support")). If the new infrastructure get extended to all arches,
this patch can be dropped.

Signed-off-by: Coiby Xu <coxu@redhat.com>
---
 kernel/crash_dump_dm_crypt.c | 30 ++++++++++++++++++++++++++----
 1 file changed, 26 insertions(+), 4 deletions(-)

diff --git a/kernel/crash_dump_dm_crypt.c b/kernel/crash_dump_dm_crypt.c
index 89fec768fba8..b4dc881cc867 100644
--- a/kernel/crash_dump_dm_crypt.c
+++ b/kernel/crash_dump_dm_crypt.c
@@ -10,12 +10,13 @@
 // The key scription has the format: cryptsetup:UUID 11+36+1(NULL)=48
 #define KEY_DESC_LEN 48
 
-static char *STATE_STR[] = {"fresh", "initialized", "recorded", "loaded"};
+static char *STATE_STR[] = {"fresh", "initialized", "recorded", "loaded", "reuse"};
 static enum STATE_ENUM {
 	FRESH = 0,
 	INITIALIZED,
 	RECORDED,
 	LOADED,
+	REUSE,
 } state;
 
 static unsigned int key_count;
@@ -90,12 +91,31 @@ static int record_key_desc(const char *buf, struct dm_crypt_key *dm_key)
 	return 0;
 }
 
+static void get_keys_from_kdump_reserved_memory(void)
+{
+	struct keys_header *keys_header_loaded;
+
+	arch_kexec_unprotect_crashkres();
+
+	keys_header_loaded = kmap_local_page(pfn_to_page(
+		kexec_crash_image->dm_crypt_keys_addr >> PAGE_SHIFT));
+
+	memcpy(keys_header, keys_header_loaded, keys_header_size);
+	kunmap_local(keys_header_loaded);
+	state = RECORDED;
+}
+
 static int process_cmd(const char *buf, size_t count)
 {
 	if (strncmp(buf, "init ", 5) == 0)
 		return init(buf);
 	else if (strncmp(buf, "record ", 7) == 0)
 		return record_key_desc(buf, &keys_header->keys[key_count]);
+	else if (!strcmp(buf, "reuse")) {
+		state = REUSE;
+		get_keys_from_kdump_reserved_memory();
+		return 0;
+	}
 
 	return -EINVAL;
 }
@@ -175,9 +195,11 @@ int crash_load_dm_crypt_keys(struct kimage *image)
 	}
 
 	image->dm_crypt_keys_addr = 0;
-	r = build_keys_header();
-	if (r)
-		return r;
+	if (state != REUSE) {
+		r = build_keys_header();
+		if (r)
+			return r;
+	}
 
 	kbuf.buffer = keys_header;
 	kbuf.bufsz = keys_header_size;
-- 
2.45.0