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bcm2835_rng: Use qcrypto_random_bytes() rather than rand()

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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: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Daniel P. Berrange <berrange@redhat.com>
This commit is contained in:
Peter Maydell 2017-02-28 12:08:14 +00:00
parent 54a5ba13a9
commit 373442ea3a
1 changed files with 26 additions and 1 deletions
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27
hw/misc/bcm2835_rng.c
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@ -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: