crypto: Assume blocksize is a power of 2

The check in the encode/decode path using full division has a
noticeable amount of overhead.  By asserting the blocksize is
a power of 2, we can reduce this check to a mask.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>

4 files changed, 9 insertions, 6 deletions

diff --git a/crypto/cipher-builtin.c b/crypto/cipher-builtin.c
index 35cf782..6eafd39 100644
--- a/crypto/cipher-builtin.c
+++ b/crypto/cipher-builtin.c
@@ -484,7 +484,7 @@ qcrypto_builtin_cipher_encrypt(QCryptoCipher *cipher,
 {
     QCryptoCipherBuiltin *ctxt = cipher->opaque;
 
-    if (len % ctxt->blocksize) {
+    if (len & (ctxt->blocksize - 1)) {
         error_setg(errp, "Length %zu must be a multiple of block size %zu",
                    len, ctxt->blocksize);
         return -1;
@@ -503,7 +503,7 @@ qcrypto_builtin_cipher_decrypt(QCryptoCipher *cipher,
 {
     QCryptoCipherBuiltin *ctxt = cipher->opaque;
 
-    if (len % ctxt->blocksize) {
+    if (len & (ctxt->blocksize - 1)) {
         error_setg(errp, "Length %zu must be a multiple of block size %zu",
                    len, ctxt->blocksize);
         return -1;
diff --git a/crypto/cipher-gcrypt.c b/crypto/cipher-gcrypt.c
index 2864099..81e4745 100644
--- a/crypto/cipher-gcrypt.c
+++ b/crypto/cipher-gcrypt.c
@@ -245,6 +245,7 @@ static QCryptoCipherGcrypt *qcrypto_cipher_ctx_new(QCryptoCipherAlgorithm alg,
             g_assert_not_reached();
         }
     }
+    g_assert(is_power_of_2(ctx->blocksize));
 
 #ifdef CONFIG_QEMU_PRIVATE_XTS
     if (mode == QCRYPTO_CIPHER_MODE_XTS) {
@@ -305,7 +306,7 @@ qcrypto_gcrypt_cipher_encrypt(QCryptoCipher *cipher,
     QCryptoCipherGcrypt *ctx = cipher->opaque;
     gcry_error_t err;
 
-    if (len % ctx->blocksize) {
+    if (len & (ctx->blocksize - 1)) {
         error_setg(errp, "Length %zu must be a multiple of block size %zu",
                    len, ctx->blocksize);
         return -1;
@@ -344,7 +345,7 @@ qcrypto_gcrypt_cipher_decrypt(QCryptoCipher *cipher,
     QCryptoCipherGcrypt *ctx = cipher->opaque;
     gcry_error_t err;
 
-    if (len % ctx->blocksize) {
+    if (len & (ctx->blocksize - 1)) {
         error_setg(errp, "Length %zu must be a multiple of block size %zu",
                    len, ctx->blocksize);
         return -1;
diff --git a/crypto/cipher-nettle.c b/crypto/cipher-nettle.c
index 7e9a4cc..0677fdf 100644
--- a/crypto/cipher-nettle.c
+++ b/crypto/cipher-nettle.c
@@ -576,6 +576,7 @@ static QCryptoCipherNettle *qcrypto_cipher_ctx_new(QCryptoCipherAlgorithm alg,
                    QCryptoCipherAlgorithm_str(alg));
         goto error;
     }
+    g_assert(is_power_of_2(ctx->blocksize));
 
     if (mode == QCRYPTO_CIPHER_MODE_XTS &&
         ctx->blocksize != XTS_BLOCK_SIZE) {
@@ -613,7 +614,7 @@ qcrypto_nettle_cipher_encrypt(QCryptoCipher *cipher,
 {
     QCryptoCipherNettle *ctx = cipher->opaque;
 
-    if (len % ctx->blocksize) {
+    if (len & (ctx->blocksize - 1)) {
         error_setg(errp, "Length %zu must be a multiple of block size %zu",
                    len, ctx->blocksize);
         return -1;
@@ -666,7 +667,7 @@ qcrypto_nettle_cipher_decrypt(QCryptoCipher *cipher,
 {
     QCryptoCipherNettle *ctx = cipher->opaque;
 
-    if (len % ctx->blocksize) {
+    if (len & (ctx->blocksize - 1)) {
         error_setg(errp, "Length %zu must be a multiple of block size %zu",
                    len, ctx->blocksize);
         return -1;
diff --git a/crypto/cipher.c b/crypto/cipher.c
index e5adb56..2722dc7 100644
--- a/crypto/cipher.c
+++ b/crypto/cipher.c
@@ -19,6 +19,7 @@
  */
 
 #include "qemu/osdep.h"
+#include "qemu/host-utils.h"
 #include "qapi/error.h"
 #include "crypto/cipher.h"
 #include "cipherpriv.h"