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 d3cc7996
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: NGreg Kurz <gkurz@linux.vnet.ibm.com>
Signed-off-by: NHerbert Xu <herbert@gondor.apana.org.au>

as pr_* macros are more preffered over printk, so printk replaced with corresponding pr_* macros
Signed-off-by: NSudip Mukherjee <sudip@vectorindia.org>
Signed-off-by: NHerbert Xu <herbert@gondor.apana.org.au>

We don't expect to get errors from the hypervisor when reading the rng,
but if we do we should pass the error up to the hwrng driver. Otherwise
the hwrng driver will continue calling us forever.
Signed-off-by: NMichael Ellerman <michael@ellerman.id.au>
Signed-off-by: NBenjamin Herrenschmidt <benh@kernel.crashing.org>

We don't expect to get errors from the hypervisor when reading the rng,
but if we do we should pass the error up to the hwrng driver. Otherwise
the hwrng driver will continue calling us forever.
Signed-off-by: NMichael Ellerman <michael@ellerman.id.au>
Signed-off-by: NHerbert Xu <herbert@gondor.apana.org.au>

Signed-off-by: NMichael Ellerman <michael@ellerman.id.au>
Signed-off-by: NHerbert Xu <herbert@gondor.apana.org.au>

Adds support for the Platform Facilities Option (PFO)-based hardware
random number generator for POWER hardware.
Signed-off-by: NMichael Neuling <mikey@neuling.org>
Signed-off-by: NRobert Jennings <rcj@linux.vnet.ibm.com>
Signed-off-by: NKent Yoder <key@linux.vnet.ibm.com>
Signed-off-by: NBenjamin Herrenschmidt <benh@kernel.crashing.org>