[PATCH, RFC 30/62] keys/mktme: Set up a percpu_ref_count for MKTME keys

[Kirill A. Shutemov]

From: Alison Schofield <alison.schofield@xxxxxxxxx>

The MKTME key service needs to keep usage counts on the encryption
keys in order to know when it is safe to free a key for reuse.

percpu_ref_count applies well here because the key service will
take the initial reference and typically hold that reference while
the intermediary references are get/put. The intermediaries in this
case are the encrypted VMA's.

Align the percpu_ref_init and percpu_ref_kill with the key service
instantiate and destroy methods respectively.

Signed-off-by: Alison Schofield <alison.schofield@xxxxxxxxx>
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
---
 security/keys/mktme_keys.c | 40 +++++++++++++++++++++++++++++++++++++-
 1 file changed, 39 insertions(+), 1 deletion(-)

diff --git a/security/keys/mktme_keys.c b/security/keys/mktme_keys.c
index f70533b1a7fd..496b5c1b7461 100644
--- a/security/keys/mktme_keys.c
+++ b/security/keys/mktme_keys.c
@@ -8,6 +8,7 @@
 #include <linux/key-type.h>
 #include <linux/mm.h>
 #include <linux/parser.h>
+#include <linux/percpu-refcount.h>
 #include <linux/random.h>
 #include <linux/string.h>
 #include <asm/intel_pconfig.h>
@@ -80,6 +81,26 @@ int mktme_keyid_from_key(struct key *key)
 	return 0;
 }
 
+struct percpu_ref *encrypt_count;
+void mktme_percpu_ref_release(struct percpu_ref *ref)
+{
+	unsigned long flags;
+	int keyid;
+
+	for (keyid = 1; keyid <= mktme_nr_keyids; keyid++) {
+		if (&encrypt_count[keyid] == ref)
+			break;
+	}
+	if (&encrypt_count[keyid] != ref) {
+		pr_debug("%s: invalid ref counter\n", __func__);
+		return;
+	}
+	percpu_ref_exit(ref);
+	spin_lock_irqsave(&mktme_map_lock, flags);
+	mktme_release_keyid(keyid);
+	spin_unlock_irqrestore(&mktme_map_lock, flags);
+}
+
 enum mktme_opt_id {
 	OPT_ERROR,
 	OPT_TYPE,
@@ -225,7 +246,10 @@ static int mktme_program_keyid(int keyid, struct mktme_payload *payload)
 /* Key Service Method called when a Userspace Key is garbage collected. */
 static void mktme_destroy_key(struct key *key)
 {
-	mktme_release_keyid(mktme_keyid_from_key(key));
+	int keyid = mktme_keyid_from_key(key);
+
+	mktme_map->key[keyid] = (void *)-1;
+	percpu_ref_kill(&encrypt_count[keyid]);
 }
 
 /* Key Service Method to create a new key. Payload is preparsed. */
@@ -241,9 +265,15 @@ int mktme_instantiate_key(struct key *key, struct key_preparsed_payload *prep)
 	if (!keyid)
 		return -ENOKEY;
 
+	if (percpu_ref_init(&encrypt_count[keyid], mktme_percpu_ref_release,
+			    0, GFP_KERNEL))
+		goto err_out;
+
 	if (!mktme_program_keyid(keyid, payload))
 		return MKTME_PROG_SUCCESS;
 
+	percpu_ref_exit(&encrypt_count[keyid]);
+err_out:
 	spin_lock_irqsave(&mktme_lock, flags);
 	mktme_release_keyid(keyid);
 	spin_unlock_irqrestore(&mktme_lock, flags);
@@ -447,10 +477,18 @@ static int __init init_mktme(void)
 	/* Initialize first programming targets */
 	mktme_update_pconfig_targets();
 
+	/* Reference counters to protect in use KeyIDs */
+	encrypt_count = kvcalloc(mktme_nr_keyids + 1, sizeof(encrypt_count[0]),
+				 GFP_KERNEL);
+	if (!encrypt_count)
+		goto free_targets;
+
 	ret = register_key_type(&key_type_mktme);
 	if (!ret)
 		return ret;			/* SUCCESS */
 
+	kvfree(encrypt_count);
+free_targets:
 	free_cpumask_var(mktme_leadcpus);
 	bitmap_free(mktme_target_map);
 free_cache:
-- 
2.20.1