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hwrng: pseries - port to new read API and fix stack corruption

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The add_early_randomness() function in drivers/char/hw_random/core.c passes
a 16-byte buffer to pseries_rng_data_read(). Unfortunately, plpar_hcall()
returns four 64-bit values and trashes 16 bytes on the stack.

This bug has been lying around for a long time. It got unveiled by:

commit d3cc799647
Author: Amit Shah <amit.shah@redhat.com>
Date:   Thu Jul 10 15:42:34 2014 +0530

    hwrng: fetch randomness only after device init

It may trig a oops while loading or unloading the pseries-rng module for both
PowerVM and PowerKVM guests.

This patch does two things:
- pass an intermediate well sized buffer to plpar_hcall(). This is acceptalbe
  since we're not on a hot path.
- move to the new read API so that we know the return buffer size for sure.

Cc: stable@vger.kernel.org
Signed-off-by: Greg Kurz <gkurz@linux.vnet.ibm.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
This commit is contained in:
Greg Kurz 2014-10-31 07:50:11 +01:00 committed by Herbert Xu
parent 738459e3f8
commit 24c65bc703
1 changed files with 7 additions and 4 deletions
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11
drivers/char/hw_random/pseries-rng.c
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@ -25,18 +25,21 @@
#include <asm/vio.h>
static int pseries_rng_data_read(struct hwrng *rng, u32 *data)
static int pseries_rng_read(struct hwrng *rng, void *data, size_t max, bool wait)
{
u64 buffer[PLPAR_HCALL_BUFSIZE];
size_t size = max < 8 ? max : 8;
int rc;
rc = plpar_hcall(H_RANDOM, (unsigned long *)data);
rc = plpar_hcall(H_RANDOM, (unsigned long *)buffer);
if (rc != H_SUCCESS) {
pr_err_ratelimited("H_RANDOM call failed %d\n", rc);
return -EIO;
}
memcpy(data, buffer, size);
/* The hypervisor interface returns 64 bits */
return 8;
return size;
}
/**
@ -55,7 +58,7 @@ static unsigned long pseries_rng_get_desired_dma(struct vio_dev *vdev)
static struct hwrng pseries_rng = {
.name = KBUILD_MODNAME,
.data_read = pseries_rng_data_read,
.read = pseries_rng_read,
};
static int __init pseries_rng_probe(struct vio_dev *dev,