From e5b9cee8681dc45340321f759079b344a3b2676c Mon Sep 17 00:00:00 2001
From: Mounir IDRASSI <mounir.idrassi@idrix.fr>
Date: Thu, 7 Feb 2019 15:24:56 +0100
Subject: Windows: Add option to enable use of CPU RDRAND/RDSEED as source of
 entropy which is now disabled by default

---
 src/Common/Apidrvr.h    |  1 +
 src/Common/Crypto.c     | 26 ++++++++++++++++++++++++++
 src/Common/Crypto.h     |  4 ++++
 src/Common/Language.xml |  1 +
 src/Common/Random.c     | 12 +++++++-----
 5 files changed, 39 insertions(+), 5 deletions(-)

(limited to 'src/Common')

diff --git a/src/Common/Apidrvr.h b/src/Common/Apidrvr.h
index 0298e204..63de40ae 100644
--- a/src/Common/Apidrvr.h
+++ b/src/Common/Apidrvr.h
@@ -417,5 +417,6 @@ typedef struct
 #define VC_DRIVER_CONFIG_BLOCK_SYS_TRIM								0x100
 #define VC_DRIVER_CONFIG_ALLOW_WINDOWS_DEFRAG						0x200
 #define VC_DRIVER_CONFIG_CLEAR_KEYS_ON_NEW_DEVICE_INSERTION			0x400
+#define VC_DRIVER_CONFIG_ENABLE_CPU_RNG								0x800
 
 #endif		/* _WIN32 */
diff --git a/src/Common/Crypto.c b/src/Common/Crypto.c
index 299595bd..a6f3ffb7 100644
--- a/src/Common/Crypto.c
+++ b/src/Common/Crypto.c
@@ -1216,3 +1216,29 @@ BOOL IsHwEncryptionEnabled ()
 }
 
 #endif // !TC_WINDOWS_BOOT
+
+#ifndef TC_WINDOWS_BOOT
+
+static BOOL CpuRngDisabled = FALSE;
+
+BOOL IsCpuRngSupport ()
+{
+	if (HasRDSEED() || HasRDSEED())
+		return TRUE;
+	else
+		return FALSE;
+}
+
+void EnableCpuRng (BOOL enable)
+{
+	CpuRngDisabled = !enable;
+}
+
+BOOL IsCpuRngEnabled ()
+{
+	return !CpuRngDisabled;
+}
+
+
+#endif
+
diff --git a/src/Common/Crypto.h b/src/Common/Crypto.h
index a362f5d1..f1b35977 100644
--- a/src/Common/Crypto.h
+++ b/src/Common/Crypto.h
@@ -385,6 +385,10 @@ BOOL IsAesHwCpuSupported ();
 void EnableHwEncryption (BOOL enable);
 BOOL IsHwEncryptionEnabled ();
 
+BOOL IsCpuRngSupport ();
+void EnableCpuRng (BOOL enable);
+BOOL IsCpuRngEnabled ();
+
 #ifdef __cplusplus
 }
 #endif
diff --git a/src/Common/Language.xml b/src/Common/Language.xml
index 47d99764..f62421de 100644
--- a/src/Common/Language.xml
+++ b/src/Common/Language.xml
@@ -1432,6 +1432,7 @@
     <entry lang="en" key="IDC_CLEAR_KEYS_ON_NEW_DEVICE_INSERTION">Clear encryption keys from memory if a new device is inserted</entry>
     <entry lang="en" key="CLEAR_KEYS_ON_DEVICE_INSERTION_WARNING">IMPORTANT NOTES:\n - Please keep in mind that this option will not persist after a shutdown/reboot so you will need to select it again next time the machine is started.\n\n - With this option enabled and after a new device is connected, the machine will freeze and it will eventually crash with a BSOD since Windows can not access the encrypted disk after its keys are cleared from memory.\n</entry>
     <entry lang="en" key="STARTING">Starting</entry>
+    <entry lang="en" key="IDC_ENABLE_CPU_RNG">Use CPU hardware random generator as an additional source of entropy</entry>
   </localization>
   <xs:schema attributeFormDefault="unqualified" elementFormDefault="qualified" xmlns:xs="http://www.w3.org/2001/XMLSchema">
     <xs:element name="VeraCrypt">
diff --git a/src/Common/Random.c b/src/Common/Random.c
index 12e9d9af..c8655b56 100644
--- a/src/Common/Random.c
+++ b/src/Common/Random.c
@@ -777,9 +777,10 @@ BOOL SlowPoll (void)
 	}
 
 	// use RDSEED or RDRAND from CPU as source of entropy if present
-	if (	(HasRDSEED() && RDSEED_getBytes (buffer, sizeof (buffer)))
+	if (	IsCpuRngEnabled() && 
+		(	(HasRDSEED() && RDSEED_getBytes (buffer, sizeof (buffer)))
 		||	(HasRDRAND() && RDRAND_getBytes (buffer, sizeof (buffer)))
-		)
+		))
 	{
 		RandaddBuf (buffer, sizeof (buffer));
 	}
@@ -907,10 +908,11 @@ BOOL FastPoll (void)
 		return FALSE;
 	}
 
-	// use RDSEED or RDRAND from CPU as source of entropy if present
-	if (	(HasRDSEED() && RDSEED_getBytes (buffer, sizeof (buffer)))
+	// use RDSEED or RDRAND from CPU as source of entropy if enabled
+	if (	IsCpuRngEnabled() && 
+		(	(HasRDSEED() && RDSEED_getBytes (buffer, sizeof (buffer)))
 		||	(HasRDRAND() && RDRAND_getBytes (buffer, sizeof (buffer)))
-		)
+		))
 	{
 		RandaddBuf (buffer, sizeof (buffer));
 	}
-- 
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