linuxkm/lkcapi_glue.c: add LINUXKM_LKCAPI_NEED_AES_COMMON_FUNCS and

  LINUXKM_LKCAPI_NEED_AES_SKCIPHER_COMMON_FUNCS helper macros (peer review
  suggestion).

wolfcrypt/src/aes.c: add lengthy comment in software wc_AesSetKeyLocal()
  explaining the dynamics of aes->use_aesni (peer review suggestion), and in the
  !haveAESNI && WC_C_DYNAMIC_FALLBACK case, return with immediate success rather
  than following through to the redundant AesSetKey_C().

Author: douzzer

linuxkm/lkcapi_glue.c

@@ -210,6 +210,29 @@ static int disable_setkey_warnings = 0;
     static int  linuxkm_test_aesecb(void);
 #endif
 
+#if defined(LINUXKM_LKCAPI_REGISTER_AESCBC) || \
+    defined(LINUXKM_LKCAPI_REGISTER_AESCFB) || \
+    defined(LINUXKM_LKCAPI_REGISTER_AESCTR) || \
+    defined(LINUXKM_LKCAPI_REGISTER_AESOFB) || \
+    defined(LINUXKM_LKCAPI_REGISTER_AESECB) || \
+    defined(LINUXKM_LKCAPI_REGISTER_AESGCM) || \
+    defined(LINUXKM_LKCAPI_REGISTER_AESGCM_RFC4106)
+    #define LINUXKM_LKCAPI_NEED_AES_COMMON_FUNCS
+#endif
+
+#if defined(LINUXKM_LKCAPI_REGISTER_AESCBC) || \
+    defined(LINUXKM_LKCAPI_REGISTER_AESCFB) || \
+    defined(LINUXKM_LKCAPI_REGISTER_AESCTR) || \
+    defined(LINUXKM_LKCAPI_REGISTER_AESOFB) || \
+    defined(LINUXKM_LKCAPI_REGISTER_AESECB)
+    #define LINUXKM_LKCAPI_NEED_AES_SKCIPHER_COMMON_FUNCS
+#endif
+
+#if defined(LINUXKM_LKCAPI_REGISTER_AESGCM) || \
+    defined(LINUXKM_LKCAPI_REGISTER_AESGCM_RFC4106)
+    #define LINUXKM_LKCAPI_REGISTER_AEADS
+#endif
+
 /* km_AesX(): wrappers to wolfcrypt wc_AesX functions and
  * structures.  */
 
@@ -312,13 +335,7 @@ struct km_AesCtx {
 #endif
 };
 
-#if defined(LINUXKM_LKCAPI_REGISTER_AESCBC) || \
-    defined(LINUXKM_LKCAPI_REGISTER_AESCFB) || \
-    defined(LINUXKM_LKCAPI_REGISTER_AESGCM) || \
-    defined(LINUXKM_LKCAPI_REGISTER_AESGCM_RFC4106) || \
-    defined(LINUXKM_LKCAPI_REGISTER_AESCTR) || \
-    defined(LINUXKM_LKCAPI_REGISTER_AESOFB) || \
-    defined(LINUXKM_LKCAPI_REGISTER_AESECB)
+#ifdef LINUXKM_LKCAPI_NEED_AES_COMMON_FUNCS
 
 static void km_AesExitCommon(struct km_AesCtx * ctx);
 
@@ -518,11 +535,7 @@ static void km_AesExitCommon(struct km_AesCtx * ctx)
 #endif
 }
 
-#if defined(LINUXKM_LKCAPI_REGISTER_AESCBC) || \
-    defined(LINUXKM_LKCAPI_REGISTER_AESCFB) || \
-    defined(LINUXKM_LKCAPI_REGISTER_AESCTR) || \
-    defined(LINUXKM_LKCAPI_REGISTER_AESOFB) || \
-    defined(LINUXKM_LKCAPI_REGISTER_AESECB)
+#ifdef LINUXKM_LKCAPI_NEED_AES_SKCIPHER_COMMON_FUNCS
 
 static int km_AesSetKeyCommon(struct km_AesCtx * ctx, const u8 *in_key,
                               unsigned int key_len, const char * name)
@@ -595,19 +608,9 @@ static void km_AesExit(struct crypto_skcipher *tfm)
     km_AesExitCommon(ctx);
 }
 
-#endif /* LINUXKM_LKCAPI_REGISTER_AESCBC ||
-        * LINUXKM_LKCAPI_REGISTER_AESCFB ||
-        * LINUXKM_LKCAPI_REGISTER_AESCTR ||
-        * LINUXKM_LKCAPI_REGISTER_AESOFB ||
-        * LINUXKM_LKCAPI_REGISTER_AESECB
-        */
-
-#endif /* LINUXKM_LKCAPI_REGISTER_AESCBC ||
-        * LINUXKM_LKCAPI_REGISTER_AESCFB || LINUXKM_LKCAPI_REGISTER_AESGCM ||
-        * LINUXKM_LKCAPI_REGISTER_AESGCM_RFC4106 ||
-        * LINUXKM_LKCAPI_REGISTER_AESCTR || LINUXKM_LKCAPI_REGISTER_AESOFB ||
-        * LINUXKM_LKCAPI_REGISTER_AESECB
-        */
+#endif /* LINUXKM_LKCAPI_NEED_AES_SKCIPHER_COMMON_FUNCS */
+
+#endif /* LINUXKM_LKCAPI_NEED_AES_COMMON_FUNCS */
 
 #ifdef LINUXKM_LKCAPI_REGISTER_AESCBC
 

wolfcrypt/src/aes.c

@@ -4575,6 +4575,36 @@ static void AesSetKey_C(Aes* aes, const byte* key, word32 keySz, int dir)
 #endif /* WC_C_DYNAMIC_FALLBACK */
 
     #ifdef WOLFSSL_AESNI
+
+       /* The dynamics for determining whether AES-NI will be used are tricky.
+        *
+        * First, we check for CPU support and cache the result -- if AES-NI is
+        * missing, we always shortcut to the AesSetKey_C() path.
+        *
+        * Second, if the CPU supports AES-NI, we confirm on a per-call basis
+        * that it's safe to use in the caller context, using
+        * SAVE_VECTOR_REGISTERS2().  This is an always-true no-op in user-space
+        * builds, but has substantive logic behind it in kernel module builds.
+        *
+        * The outcome when SAVE_VECTOR_REGISTERS2() fails depends on
+        * WC_C_DYNAMIC_FALLBACK -- if that's defined, we return immediately with
+        * success but with AES-NI disabled (the earlier AesSetKey_C() allows
+        * future encrypt/decrypt calls to succeed), otherwise we fail.
+        *
+        * Upon successful return, aes->use_aesni will have a zero value if
+        * AES-NI is disabled, and a nonzero value if it's enabled.
+        *
+        * An additional, optional semantic is available via
+        * WC_FLAG_DONT_USE_AESNI, and is used in some kernel module builds to
+        * let the caller inhibit AES-NI.  When this macro is defined,
+        * wc_AesInit() before wc_AesSetKey() is imperative, to avoid a read of
+        * uninitialized data in aes->use_aesni.  That's why support for
+        * WC_FLAG_DONT_USE_AESNI must remain optional -- wc_AesInit() was only
+        * added in release 3.11.0, so legacy applications inevitably call
+        * wc_AesSetKey() on uninitialized Aes contexts.  This must continue to
+        * function correctly with default build settings.
+        */
+
         if (checkedAESNI == 0) {
             haveAESNI  = Check_CPU_support_AES();
             checkedAESNI = 1;
@@ -4627,6 +4657,12 @@ static void AesSetKey_C(Aes* aes, const byte* key, word32 keySz, int dir)
         }
         else {
             aes->use_aesni = 0;
+#ifdef WC_C_DYNAMIC_FALLBACK
+            /* If WC_C_DYNAMIC_FALLBACK, we already called AesSetKey_C()
+             * above.
+             */
+            return 0;
+#endif
         }
     #endif /* WOLFSSL_AESNI */
 

wolfssl/wolfcrypt/aes.h

@@ -306,7 +306,8 @@ struct Aes {
     #if defined(WOLFSSL_LINUXKM) || defined(WC_WANT_FLAG_DONT_USE_AESNI)
         /* Note, we can't support WC_FLAG_DONT_USE_AESNI by default because we
          * need to support legacy applications that call wc_AesSetKey() on
-         * uninited struct Aes.
+         * uninited struct Aes.  For details see the software implementation of
+         * wc_AesSetKeyLocal() (aes.c).
          */
         #define WC_FLAG_DONT_USE_AESNI 2
     #endif