[PATCH v4 5/7] crash_dump: retrieve dm crypt keys in kdump kernel

Coiby Xu
2024-05-23T05:05:18Z

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@redhat.com>
---
include/linux/crash_core.h | 1 +
kernel/crash_dump_dm_crypt.c | 99 +++++++++++++++++++++++++++++++++++-
2 files changed, 99 insertions(+), 1 deletion(-)

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 b4dc881cc867..dd818581858b 100644
--- a/kernel/crash_dump_dm_crypt.c
+++ b/kernel/crash_dump_dm_crypt.c
@@ -33,12 +33,67 @@ static struct keys_header {
struct dm_crypt_key keys[] __counted_by(key_count);
} *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 key_count)
{
return struct_size(keys_header, keys, key_count);
}

+/*
+ * Architectures may override this function to read dm crypt key
+ */
+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);
+ pr_alert("Success adding key %s", dm_key->key_desc);
+ } else {
+ r = PTR_ERR(key_ref);
+ pr_alert("Error when adding key");
+ }
+
+ key_ref_put(keyring_ref);
+ return r;
+}
+
static int init(const char *buf)
{
unsigned int total_keys;
@@ -120,11 +175,53 @@ 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)) {
+ pr_alert("Failed to get keyring");
+ 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 the number of dm_crypt keys\n");
+ return -1;
+ }
+
+ pr_debug("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->key_count; i++) {
+ key = &keys_header->keys[i];
+ pr_alert("Get key (size=%u): %8ph...\n", key->key_size, key->data);
+ 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(crash_sysfs_dm_crypt_keys_write);

--
2.45.0