Commit 373442ea authored by Peter Maydell's avatar Peter Maydell
Browse files

bcm2835_rng: Use qcrypto_random_bytes() rather than rand() 



Switch to using qcrypto_random_bytes() rather than rand() as
our source of randomness for the BCM2835 RNG.

If qcrypto_random_bytes() fails, we don't want to return the guest a
non-random value in case they're really using it for cryptographic
purposes, so the best we can do is a fatal error.  This shouldn't
happen unless something's broken, though.

In theory we could implement this device's full FIFO and interrupt
semantics and then just stop filling the FIFO.  That's a lot of work,
though, and doesn't really give a very nice diagnostic to the user
since the guest will just seem to hang.

Signed-off-by: default avatarPeter Maydell <peter.maydell@linaro.org>
Reviewed-by: default avatarDaniel P. Berrange <berrange@redhat.com>
parent 54a5ba13

hw/misc/bcm2835_rng.c

+26 −1
Original line number Diff line number Diff line
@@ -9,8 +9,33 @@ 


#include "qemu/osdep.h"

#include "qemu/log.h"

#include "qapi/error.h"

#include "crypto/random.h"

#include "hw/misc/bcm2835_rng.h"



static uint32_t get_random_bytes(void)

{

    uint32_t res;

    Error *err = NULL;



    if (qcrypto_random_bytes((uint8_t *)&res, sizeof(res), &err) < 0) {

        /* On failure we don't want to return the guest a non-random

         * value in case they're really using it for cryptographic

         * purposes, so the best we can do is die here.

         * This shouldn't happen unless something's broken.

         * In theory we could implement this device's full FIFO

         * and interrupt semantics and then just stop filling the

         * FIFO. That's a lot of work, though, so we assume any

         * errors are systematic problems and trust that if we didn't

         * fail as the guest inited then we won't fail later on

         * mid-run.

         */

        error_report_err(err);

        exit(1);

    }

    return res;

}



static uint64_t bcm2835_rng_read(void *opaque, hwaddr offset,

                                 unsigned size)

{
@@ -27,7 +52,7 @@ static uint64_t bcm2835_rng_read(void *opaque, hwaddr offset, 
        res = s->rng_status | (1 << 24);

        break;

    case 0x8:    /* rng_data */

        res = rand();

        res = get_random_bytes();

        break;



    default: