[PATCHv2 31/59] keys/mktme: Set up a percpu_ref_count for MKTME keys

Kirill A. Shutemov
2019-07-31T15:20:55Z

From: Alison Schofield <alison.schofield@intel.com>

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 will be 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@intel.com>
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
---
security/keys/mktme_keys.c | 39 +++++++++++++++++++++++++++++++++++++-
1 file changed, 38 insertions(+), 1 deletion(-)

diff --git a/security/keys/mktme_keys.c b/security/keys/mktme_keys.c
index 3c641f3ee794..18cb57be5193 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/string.h>
#include <asm/intel_pconfig.h>
#include <keys/mktme-type.h>
@@ -71,6 +72,26 @@ 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_lock, flags);
+ mktme_release_keyid(keyid);
+ spin_unlock_irqrestore(&mktme_lock, flags);
+}
+
enum mktme_opt_id {
OPT_ERROR,
OPT_TYPE,
@@ -199,8 +220,10 @@ static void mktme_destroy_key(struct key *key)
unsigned long flags;

spin_lock_irqsave(&mktme_lock, flags);
- mktme_release_keyid(keyid);
+ mktme_map[keyid].key = NULL;
+ mktme_map[keyid].state = KEYID_REF_KILLED;
spin_unlock_irqrestore(&mktme_lock, flags);
+ percpu_ref_kill(&encrypt_count[keyid]);
}

/* Key Service Method to create a new key. Payload is preparsed. */
@@ -216,9 +239,15 @@ 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);
@@ -405,10 +434,18 @@ 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:
--
2.21.0