[PATCH v5 5/7] crash_dump: retrieve dm crypt keys in kdump kernel

[Coiby Xu]

Crash kernel will retrieve the dm crypt keys based on the dmcryptkeys
command line parameter. When user space writes the key description to
/sys/kernel/crash_dm_crypt_key, the crash kernel will save the
encryption keys to the user keyring. Then user space e.g. cryptsetup's
--volume-key-keyring API can use it to unlock the encrypted device.

Signed-off-by: Coiby Xu <coxu@xxxxxxxxxx>
---
 Documentation/ABI/testing/crash_dm_crypt_keys |   3 +
 include/linux/crash_core.h                    |   1 +
 kernel/crash_dump_dm_crypt.c                  | 101 +++++++++++++++++-
 3 files changed, 103 insertions(+), 2 deletions(-)

diff --git a/Documentation/ABI/testing/crash_dm_crypt_keys b/Documentation/ABI/testing/crash_dm_crypt_keys
index 7426c9d8de97..56a4b878a4dd 100644
--- a/Documentation/ABI/testing/crash_dm_crypt_keys
+++ b/Documentation/ABI/testing/crash_dm_crypt_keys
@@ -29,4 +29,7 @@ Description:	read/write
         the kdump kernel has been loaded with the dm crypt keys stored to kdump
         reserved memory
 
+    After the kdump kernel gets booted, user space can write anything to this API
+    so the dm crypt keys can be restored to the keyring.
+
 User:		Kdump service
diff --git a/include/linux/crash_core.h b/include/linux/crash_core.h
index ab20829d0bc9..d7308b6e83f4 100644
--- a/include/linux/crash_core.h
+++ b/include/linux/crash_core.h
@@ -38,6 +38,7 @@ static inline void arch_kexec_unprotect_crashkres(void) { }
 int crash_sysfs_dm_crypt_keys_read(char *buf);
 int crash_sysfs_dm_crypt_keys_write(const char *buf, size_t count);
 int crash_load_dm_crypt_keys(struct kimage *image);
+ssize_t dm_crypt_keys_read(char *buf, size_t count, u64 *ppos);
 #else
 static inline int crash_load_dm_crypt_keys(struct kimage *image) {return 0; }
 #endif
diff --git a/kernel/crash_dump_dm_crypt.c b/kernel/crash_dump_dm_crypt.c
index 9a6bd39adf76..00223343473b 100644
--- a/kernel/crash_dump_dm_crypt.c
+++ b/kernel/crash_dump_dm_crypt.c
@@ -40,12 +40,67 @@ static struct keys_header {
 	struct dm_crypt_key keys[] __counted_by(total_keys);
 } *keys_header;
 
+unsigned long long dm_crypt_keys_addr;
+EXPORT_SYMBOL_GPL(dm_crypt_keys_addr);
+
+static int __init setup_dmcryptkeys(char *arg)
+{
+	char *end;
+
+	if (!arg)
+		return -EINVAL;
+	dm_crypt_keys_addr = memparse(arg, &end);
+	if (end > arg)
+		return 0;
+
+	dm_crypt_keys_addr = 0;
+	return -EINVAL;
+}
+
+early_param("dmcryptkeys", setup_dmcryptkeys);
+
 static size_t get_keys_header_size(struct keys_header *keys_header,
 				   size_t total_keys)
 {
 	return struct_size(keys_header, keys, total_keys);
 }
 
+/*
+ * Architectures may override this function to read dm crypt keys
+ */
+ssize_t __weak dm_crypt_keys_read(char *buf, size_t count, u64 *ppos)
+{
+	struct kvec kvec = { .iov_base = buf, .iov_len = count };
+	struct iov_iter iter;
+
+	iov_iter_kvec(&iter, READ, &kvec, 1, count);
+	return read_from_oldmem(&iter, count, ppos, false);
+}
+
+static int add_key_to_keyring(struct dm_crypt_key *dm_key,
+			      key_ref_t keyring_ref)
+{
+	key_ref_t key_ref;
+	int r;
+
+	/* create or update the requested key and add it to the target keyring */
+	key_ref = key_create_or_update(keyring_ref, "user", dm_key->key_desc,
+				       dm_key->data, dm_key->key_size,
+				       KEY_USR_ALL, KEY_ALLOC_IN_QUOTA);
+
+	if (!IS_ERR(key_ref)) {
+		r = key_ref_to_ptr(key_ref)->serial;
+		key_ref_put(key_ref);
+		kexec_dprintk("Success adding key %s", dm_key->key_desc);
+	} else {
+		r = PTR_ERR(key_ref);
+		kexec_dprintk("Error when adding key");
+	}
+
+	key_ref_put(keyring_ref);
+	return r;
+}
+
 /*
  * Let the kernel know the number of dm crypt keys and allocate memory to
  * initialize related structures.
@@ -139,11 +194,53 @@ static int process_cmd(const char *buf, size_t count)
 	return -EINVAL;
 }
 
+static int restore_dm_crypt_keys_to_thread_keyring(const char *key_desc)
+{
+	struct dm_crypt_key *key;
+	key_ref_t keyring_ref;
+	u64 addr;
+
+	/* find the target keyring (which must be writable) */
+	keyring_ref =
+		lookup_user_key(KEY_SPEC_USER_KEYRING, 0x01, KEY_NEED_WRITE);
+	if (IS_ERR(keyring_ref)) {
+		kexec_dprintk("Failed to get keyring %s\n", key_desc);
+		return PTR_ERR(keyring_ref);
+	}
+
+	addr = dm_crypt_keys_addr;
+	dm_crypt_keys_read((char *)&key_count, sizeof(key_count), &addr);
+	if (key_count < 0 || key_count > KEY_NUM_MAX) {
+		pr_info("Failed to read the number of dm_crypt keys\n");
+		return -1;
+	}
+
+	kexec_dprintk("There are %u keys\n", key_count);
+	addr = dm_crypt_keys_addr;
+
+	keys_header_size = get_keys_header_size(keys_header, key_count);
+
+	keys_header = kzalloc(keys_header_size, GFP_KERNEL);
+	if (!keys_header)
+		return -ENOMEM;
+
+	dm_crypt_keys_read((char *)keys_header, keys_header_size, &addr);
+
+	for (int i = 0; i < keys_header->total_keys; i++) {
+		key = &keys_header->keys[i];
+		kexec_dprintk("Get key (size=%u)\n", key->key_size);
+		add_key_to_keyring(key, keyring_ref);
+	}
+
+	return 0;
+}
+
 int crash_sysfs_dm_crypt_keys_write(const char *buf, size_t count)
 {
 	if (!is_kdump_kernel())
 		return process_cmd(buf, count);
-	return -EINVAL;
+	else
+		return restore_dm_crypt_keys_to_thread_keyring(buf);
 }
 EXPORT_SYMBOL_GPL(crash_sysfs_dm_crypt_keys_write);
 
@@ -184,7 +281,7 @@ static int build_keys_header(void)
 	for (i = 0; i < key_count; i++) {
 		r = read_key_from_user_keying(&keys_header->keys[i]);
 		if (r != 0) {
-			pr_err("Failed to read key %s\n", keys_header->keys[i].key_desc);
+			kexec_dprintk("Failed to read key %s\n", keys_header->keys[i].key_desc);
 			return r;
 		}
 	}
-- 
2.45.1