rdrand.c File Reference

Hardware random number generator. More...

#include <errno.h>
#include <ipxe/cpuid.h>
#include <ipxe/entropy.h>
#include <ipxe/drbg.h>

Go to the source code of this file.

Macros
#define	RDRAND_RETRY_COUNT   16
	Number of times to retry RDRAND instruction. More...
#define	colour   &rdrand_entropy
	Colour for debug messages. More...

Functions
	FILE_LICENCE (GPL2_OR_LATER_OR_UBDL)
	FILE_SECBOOT (PERMITTED)
struct entropy_source rdrand_entropy	__entropy_source (ENTROPY_PREFERRED)
	Hardware random number generator entropy source. More...
static int	rdrand_entropy_enable (void)
	Enable entropy gathering. More...
static int	rdrand_get_noise (noise_sample_t *noise)
	Get noise sample. More...

Detailed Description

Hardware random number generator.

Definition in file rdrand.c.

Macro Definition Documentation

RDRAND_RETRY_COUNT

#define RDRAND_RETRY_COUNT   16

Number of times to retry RDRAND instruction.

Definition at line 41 of file rdrand.c.

colour

#define colour   &rdrand_entropy

Colour for debug messages.

Definition at line 44 of file rdrand.c.

Function Documentation

FILE_LICENCE()

FILE_LICENCE

(

GPL2_OR_LATER_OR_UBDL

)

FILE_SECBOOT()

FILE_SECBOOT

(

PERMITTED

)

__entropy_source()

struct entropy_source rdrand_entropy __entropy_source

(

ENTROPY_PREFERRED

)

Initial value:

= {
        .name = "rdrand",
        .enable = rdrand_entropy_enable,
        .get_noise = rdrand_get_noise,
}

Hardware random number generator entropy source.

rdrand_entropy_enable()

static int rdrand_entropy_enable ( void  )

static

Enable entropy gathering.

Return values

rc	Return status code

Definition at line 51 of file rdrand.c.

                                          {
        struct x86_features features;

        /* Check that RDRAND is supported */
        x86_features ( &features );
        if ( ! ( features.intel.ecx & CPUID_FEATURES_INTEL_ECX_RDRAND ) ) {
                DBGC ( colour, "RDRAND not supported\n" );
                return -ENOTSUP;
        }

        /* Data returned by RDRAND is theoretically full entropy, up
         * to a security strength of 128 bits, so assume that each
         * sample contains exactly 8 bits of entropy.
         */
        if ( DRBG_SECURITY_STRENGTH > 128 )
                return -ENOTSUP;
        entropy_init ( &rdrand_entropy, MIN_ENTROPY ( 8.0 ) );

        return 0;
}

References colour, CPUID_FEATURES_INTEL_ECX_RDRAND, DBGC, DRBG_SECURITY_STRENGTH, ENOTSUP, entropy_init(), features, MIN_ENTROPY, and x86_features().

rdrand_get_noise()

static int rdrand_get_noise ( noise_sample_t *  noise )

static

Get noise sample.

Return values

noise	Noise sample
rc	Return status code

Definition at line 78 of file rdrand.c.

                                                      {
        unsigned int result;
        unsigned int discard_c;
        unsigned int ok;

        /* Issue RDRAND, retrying until CF is set */
        __asm__ ( "\n1:\n\t"
                  "rdrand %0\n\t"
                  "sbb %1, %1\n\t"
                  "loopz 1b\n\t"
                  : "=r" ( result ), "=r" ( ok ), "=c" ( discard_c )
                  : "2" ( RDRAND_RETRY_COUNT ) );
        if ( ! ok ) {
                DBGC ( colour, "RDRAND failed to become ready\n" );
                return -EBUSY;
        }

        *noise = result;
        return 0;
}

References __asm__(), colour, DBGC, discard_c, EBUSY, ok, RDRAND_RETRY_COUNT, and result.