[PATCH v2 3/5] crash_dump: retrieve dm crypt key in kdump kernel

[Coiby Xu]

Crash kernel will retrieve the dm crypt volume key based on the
dmcryptkey command line parameter. When user space writes the key
description to /sys/kernel/crash_dm_crypt_key, the crash kernel will
save the encryption key 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 at redhat.com>
---
 include/linux/crash_dump.h   |   2 +
 kernel/crash_dump_dm_crypt.c | 115 ++++++++++++++++++++++++++++++++++-
 2 files changed, 116 insertions(+), 1 deletion(-)

diff --git a/include/linux/crash_dump.h b/include/linux/crash_dump.h
index acc55626afdc..b44adc3962da 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 luks_volume_key_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 3a0b0b773598..755017fa5c1b 100644
--- a/kernel/crash_dump_dm_crypt.c
+++ b/kernel/crash_dump_dm_crypt.c
@@ -1,7 +1,82 @@
 // SPDX-License-Identifier: GPL-2.0-only
+#include <linux/key.h>
+#include <linux/keyctl.h>
 #include <keys/user-type.h>
 #include <linux/crash_dump.h>
 
+unsigned long long dm_crypt_key_addr;
+EXPORT_SYMBOL_GPL(dm_crypt_key_addr);
+
+static int __init setup_dmcryptkey(char *arg)
+{
+	char *end;
+
+	if (!arg)
+		return -EINVAL;
+	dm_crypt_key_addr = memparse(arg, &end);
+	if (end > arg)
+		return 0;
+
+	dm_crypt_key_addr = 0;
+	return -EINVAL;
+}
+
+early_param("dmcryptkey", setup_dmcryptkey);
+
+/*
+ * Architectures may override this function to read dm crypt key
+ */
+ssize_t __weak dm_crypt_key_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 retrive_kdump_dm_crypt_key(u8 *buffer, unsigned int *sz)
+{
+	unsigned int key_size;
+	size_t dm_crypt_keybuf_sz;
+	unsigned int *size_ptr;
+	char *dm_crypt_keybuf;
+	u64 addr;
+	int r;
+
+	if (dm_crypt_key_addr == 0) {
+		pr_debug("dm crypt key memory address inaccessible");
+		return -EINVAL;
+	}
+
+	addr = dm_crypt_key_addr;
+
+	/* Read dm crypt key size */
+	r = dm_crypt_key_read((char *)&key_size, sizeof(unsigned int), &addr);
+
+	if (r < 0)
+		return r;
+
+	pr_debug("Retrieve dm crypt key: size=%u\n", key_size);
+	/* Read in dm cryptrkey */
+	dm_crypt_keybuf_sz = sizeof(unsigned int) + key_size * sizeof(u8);
+	dm_crypt_keybuf = (void *)__get_free_pages(GFP_KERNEL | __GFP_ZERO,
+					      get_order(dm_crypt_keybuf_sz));
+	if (!dm_crypt_keybuf)
+		return -ENOMEM;
+
+	addr = dm_crypt_key_addr;
+	r = dm_crypt_key_read((char *)dm_crypt_keybuf, dm_crypt_keybuf_sz, &addr);
+
+	if (r < 0)
+		return r;
+	size_ptr = (unsigned int *)dm_crypt_keybuf;
+	memcpy(buffer, size_ptr + 1, key_size * sizeof(u8));
+	pr_debug("Retrieve dm crypt key (size=%u): %48ph...\n", key_size, buffer);
+	*sz = key_size;
+	return 0;
+}
+
 static u8 *dm_crypt_key;
 static unsigned int dm_crypt_key_size;
 
@@ -23,6 +98,43 @@ static DECLARE_DELAYED_WORK(wipe_dm_crypt_key_work, _wipe_dm_crypt_key);
 
 static unsigned __read_mostly wipe_key_delay = 120; /* 2 mins */
 
+static int retore_dm_crypt_key_to_thread_keyring(const char *key_desc)
+{
+	key_ref_t keyring_ref, key_ref;
+	int ret;
+
+	/* 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);
+	}
+
+	dm_crypt_key = kmalloc(128, GFP_KERNEL);
+	ret = retrive_kdump_dm_crypt_key(dm_crypt_key, &dm_crypt_key_size);
+	if (ret) {
+		kfree(dm_crypt_key);
+		return ret;
+	}
+
+	/* create or update the requested key and add it to the target keyring */
+	key_ref = key_create_or_update(keyring_ref, "user", key_desc,
+				       dm_crypt_key, dm_crypt_key_size,
+				       KEY_USR_ALL, KEY_ALLOC_IN_QUOTA);
+
+	if (!IS_ERR(key_ref)) {
+		ret = key_ref_to_ptr(key_ref)->serial;
+		key_ref_put(key_ref);
+		pr_alert("Success adding key %s", key_desc);
+	} else {
+		ret = PTR_ERR(key_ref);
+		pr_alert("Error when adding key");
+	}
+
+	key_ref_put(keyring_ref);
+	return ret;
+}
+
 static int crash_save_temp_dm_crypt_key(const char *key_desc, size_t count)
 {
 	const struct user_key_payload *ukp;
@@ -60,7 +172,8 @@ int crash_sysfs_dm_crypt_key_write(const char *key_desc, size_t count)
 {
 	if (!is_kdump_kernel())
 		return crash_save_temp_dm_crypt_key(key_desc, count);
-	return -EINVAL;
+	else
+		return retore_dm_crypt_key_to_thread_keyring(key_desc);
 }
 EXPORT_SYMBOL(crash_sysfs_dm_crypt_key_write);
 
-- 
2.43.0