1 files changed, 57 insertions, 7 deletions

diff --git a/crypto/pbkdf.c b/crypto/pbkdf.c
index 8d198c1..2989fc0 100644
--- a/crypto/pbkdf.c
+++ b/crypto/pbkdf.c
@@ -19,6 +19,7 @@
  */
 
 #include "qemu/osdep.h"
+#include "qemu/thread.h"
 #include "qapi/error.h"
 #include "crypto/pbkdf.h"
 #ifndef _WIN32
@@ -85,12 +86,28 @@ static int qcrypto_pbkdf2_get_thread_cpu(unsigned long long *val_ms,
 #endif
 }
 
-uint64_t qcrypto_pbkdf2_count_iters(QCryptoHashAlgorithm hash,
-                                    const uint8_t *key, size_t nkey,
-                                    const uint8_t *salt, size_t nsalt,
-                                    size_t nout,
-                                    Error **errp)
+typedef struct CountItersData {
+    QCryptoHashAlgo hash;
+    const uint8_t *key;
+    size_t nkey;
+    const uint8_t *salt;
+    size_t nsalt;
+    size_t nout;
+    uint64_t iterations;
+    Error **errp;
+} CountItersData;
+
+static void *threaded_qcrypto_pbkdf2_count_iters(void *data)
 {
+    CountItersData *iters_data = (CountItersData *) data;
+    QCryptoHashAlgo hash = iters_data->hash;
+    const uint8_t *key = iters_data->key;
+    size_t nkey = iters_data->nkey;
+    const uint8_t *salt = iters_data->salt;
+    size_t nsalt = iters_data->nsalt;
+    size_t nout = iters_data->nout;
+    Error **errp = iters_data->errp;
+    size_t scaled = 0;
     uint64_t ret = -1;
     g_autofree uint8_t *out = g_new(uint8_t, nout);
     uint64_t iterations = (1 << 15);
@@ -114,13 +131,27 @@ uint64_t qcrypto_pbkdf2_count_iters(QCryptoHashAlgorithm hash,
 
         delta_ms = end_ms - start_ms;
 
-        if (delta_ms > 500) {
+        /*
+         * For very small 'iterations' values, CPU (or crypto
+         * accelerator) might be fast enough that the scheduler
+         * hasn't incremented getrusage() data, or incremented
+         * it by a very small amount, resulting in delta_ms == 0.
+         * Once we've scaled 'iterations' x10, 5 times, we really
+         * should be seeing delta_ms != 0, so sanity check at
+         * that point.
+         */
+        if (scaled > 5 &&
+            delta_ms == 0) { /* sanity check */
+            error_setg(errp, "Unable to get accurate CPU usage");
+            goto cleanup;
+        } else if (delta_ms > 500) {
             break;
         } else if (delta_ms < 100) {
             iterations = iterations * 10;
         } else {
             iterations = (iterations * 1000 / delta_ms);
         }
+        scaled++;
     }
 
     iterations = iterations * 1000 / delta_ms;
@@ -129,5 +160,24 @@ uint64_t qcrypto_pbkdf2_count_iters(QCryptoHashAlgorithm hash,
 
  cleanup:
     memset(out, 0, nout);
-    return ret;
+    iters_data->iterations = ret;
+    return NULL;
+}
+
+uint64_t qcrypto_pbkdf2_count_iters(QCryptoHashAlgo hash,
+                                    const uint8_t *key, size_t nkey,
+                                    const uint8_t *salt, size_t nsalt,
+                                    size_t nout,
+                                    Error **errp)
+{
+    CountItersData data = {
+        hash, key, nkey, salt, nsalt, nout, 0, errp
+    };
+    QemuThread thread;
+
+    qemu_thread_create(&thread, "pbkdf2", threaded_qcrypto_pbkdf2_count_iters,
+                       &data, QEMU_THREAD_JOINABLE);
+    qemu_thread_join(&thread);
+
+    return data.iterations;
 }