[PATCH v6 5/7] crash_dump: retrieve dm crypt keys in kdump kernel

Coiby Xu
2024-10-29T05:53:06Z

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/config/crash_dm_crypt_key/restore, 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@redhat.com>
---
include/linux/crash_core.h | 1 +
include/linux/crash_dump.h | 2 +
kernel/crash_dump_dm_crypt.c | 134 ++++++++++++++++++++++++++++++++++-
3 files changed, 136 insertions(+), 1 deletion(-)

diff --git a/include/linux/crash_core.h b/include/linux/crash_core.h
index 2e6782239034..d35726d6a415 100644
--- a/include/linux/crash_core.h
+++ b/include/linux/crash_core.h
@@ -36,6 +36,7 @@ static inline void arch_kexec_unprotect_crashkres(void) { }

#ifdef CONFIG_CRASH_DM_CRYPT
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/include/linux/crash_dump.h b/include/linux/crash_dump.h
index acc55626afdc..dfd8e4fe6129 100644
--- a/include/linux/crash_dump.h
+++ b/include/linux/crash_dump.h
@@ -15,6 +15,8 @@
extern unsigned long long elfcorehdr_addr;
extern unsigned long long elfcorehdr_size;

+extern unsigned long long dm_crypt_keys_addr;
+
#ifdef CONFIG_CRASH_DUMP
extern int elfcorehdr_alloc(unsigned long long *addr, unsigned long long *size);
extern void elfcorehdr_free(unsigned long long addr);
diff --git a/kernel/crash_dump_dm_crypt.c b/kernel/crash_dump_dm_crypt.c
index 51431f93fc1e..f72a88b7d106 100644
--- a/kernel/crash_dump_dm_crypt.c
+++ b/kernel/crash_dump_dm_crypt.c
@@ -3,6 +3,7 @@
#include <linux/keyctl.h>
#include <keys/user-type.h>
#include <linux/crash_dump.h>
+#include <linux/cc_platform.h>
#include <linux/configfs.h>
#include <linux/module.h>

@@ -28,6 +29,61 @@ static size_t get_keys_header_size(size_t total_keys)
return struct_size(keys_header, keys, total_keys);
}

+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);
+
+/*
+ * 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, cc_platform_has(CC_ATTR_MEM_ENCRYPT));
+}
+
+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;
+}
+
static void get_keys_from_kdump_reserved_memory(void)
{
struct keys_header *keys_header_loaded;
@@ -42,6 +98,47 @@ static void get_keys_from_kdump_reserved_memory(void)
arch_kexec_protect_crashkres();
}

+static int restore_dm_crypt_keys_to_thread_keyring(void)
+{
+ struct dm_crypt_key *key;
+ size_t keys_header_size;
+ 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 the user keyring\n");
+ 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) {
+ kexec_dprintk("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(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;
+}
+
static int read_key_from_user_keying(struct dm_crypt_key *dm_key)
{
const struct user_key_payload *ukp;
@@ -211,6 +308,37 @@ static const struct config_item_type config_keys_type = {
.ct_owner = THIS_MODULE,
};

+static bool restore;
+
+static ssize_t config_keys_restore_show(struct config_item *item, char *page)
+{
+ return sprintf(page, "%d\n", restore);
+}
+
+static ssize_t config_keys_restore_store(struct config_item *item,
+ const char *page, size_t count)
+{
+ if (!restore)
+ restore_dm_crypt_keys_to_thread_keyring();
+
+ if (kstrtobool(page, &restore))
+ return -EINVAL;
+
+ return count;
+}
+
+CONFIGFS_ATTR(config_keys_, restore);
+
+static struct configfs_attribute *kdump_config_keys_attrs[] = {
+ &config_keys_attr_restore,
+ NULL,
+};
+
+static const struct config_item_type kdump_config_keys_type = {
+ .ct_attrs = kdump_config_keys_attrs,
+ .ct_owner = THIS_MODULE,
+};
+
static struct configfs_subsystem config_keys_subsys = {
.su_group = {
.cg_item = {
@@ -302,11 +430,15 @@ int crash_load_dm_crypt_keys(struct kimage *image)
return r;
}

-
static int __init configfs_dmcrypt_keys_init(void)
{
int ret;

+ if (is_kdump_kernel()) {
+ config_keys_subsys.su_group.cg_item.ci_type =
+ &kdump_config_keys_type;
+ }
+
config_group_init(&config_keys_subsys.su_group);
mutex_init(&config_keys_subsys.su_mutex);
ret = configfs_register_subsystem(&config_keys_subsys);
--
2.47.0