[rng] Add Linux entropy source using /dev/random

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/include/ipxe/entropy.h

@@ -54,6 +54,7 @@ typedef uint8_t entropy_sample_t;
 
 /* Include all architecture-independent entropy API headers */
 #include <ipxe/null_entropy.h>
+#include <ipxe/linux/linux_entropy.h>
 
 /* Include all architecture-dependent entropy API headers */
 #include <bits/entropy.h>

src/include/ipxe/errfile.h

@@ -247,6 +247,7 @@ FILE_LICENCE ( GPL2_OR_LATER );
 #define ERRFILE_drbg		      ( ERRFILE_OTHER | 0x00250000 )
 #define ERRFILE_entropy		      ( ERRFILE_OTHER | 0x00260000 )
 #define ERRFILE_rsa		      ( ERRFILE_OTHER | 0x00270000 )
+#define ERRFILE_linux_entropy	      ( ERRFILE_OTHER | 0x00280000 )
 
 /** @} */
 

src/include/ipxe/linux/linux_entropy.h

@@ -0,0 +1,32 @@
+#ifndef _IPXE_LINUX_ENTROPY_H
+#define _IPXE_LINUX_ENTROPY_H
+
+/** @file
+ *
+ * iPXE entropy API for linux
+ *
+ */
+
+FILE_LICENCE(GPL2_OR_LATER);
+
+#ifdef ENTROPY_LINUX
+#define ENTROPY_PREFIX_linux
+#else
+#define ENTROPY_PREFIX_linux __linux_
+#endif
+
+/**
+ * min-entropy per sample
+ *
+ * @ret min_entropy	min-entropy of each sample
+ */
+static inline __always_inline double
+ENTROPY_INLINE ( linux, min_entropy_per_sample ) ( void ) {
+
+	/* We read single bytes from /dev/random and assume that each
+	 * contains full entropy.
+	 */
+	return 8;
+}
+
+#endif /* _IPXE_LINUX_ENTROPY_H */