commit 552e8f2d6a28bdd664f01da2564ea261dcf56477
author Jarno Lamsa <jarno.lamsa@arm.com> Thu Nov 14 10:05:36 2019 +0200
committer Jarno Lamsa <jarno.lamsa@arm.com> Thu Dec 19 07:56:10 2019 +0200
tree 7f076fe4e3fe74b4d2473fad6746d11e17c3d552
parent 4708d66af5426a03da9e8e998d8ec4d01e63c7d1

Add double check to entropy-loop

To prevent glitching and going through without strong source

library/entropy.c

diff --git a/library/entropy.c b/library/entropy.c
index 75421cf..fdb2e15 100644
--- a/library/entropy.c
+++ b/library/entropy.c
@@ -258,7 +258,8 @@
  */
 static int entropy_gather_internal( mbedtls_entropy_context *ctx )
 {
-    int ret, i, have_one_strong = 0;
+    int ret, i;
+    volatile int have_one_strong_fi = 0;
     unsigned char buf[MBEDTLS_ENTROPY_MAX_GATHER];
     size_t olen;
 
@@ -271,7 +272,7 @@
     for( i = 0; i < ctx->source_count; i++ )
     {
         if( ctx->source[i].strong == MBEDTLS_ENTROPY_SOURCE_STRONG )
-            have_one_strong = 1;
+            have_one_strong_fi = 1;
 
         olen = 0;
         if( ( ret = ctx->source[i].f_source( ctx->source[i].p_source,
@@ -292,8 +293,14 @@
         }
     }
 
-    if( have_one_strong == 0 )
-        ret = MBEDTLS_ERR_ENTROPY_NO_STRONG_SOURCE;
+    if( have_one_strong_fi == 0 )
+    {
+        mbedtls_platform_enforce_volatile_reads();
+        if( have_one_strong_fi == 0)
+        {
+            ret = MBEDTLS_ERR_ENTROPY_NO_STRONG_SOURCE;
+        }
+    }
 
 cleanup:
     mbedtls_platform_zeroize( buf, sizeof( buf ) );