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Commit 24c65bc7 authored by Greg Kurz's avatar Greg Kurz Committed by Herbert Xu
Browse files

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



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: default avatarGreg Kurz <gkurz@linux.vnet.ibm.com>
Signed-off-by: default avatarHerbert Xu <herbert@gondor.apana.org.au>
parent 738459e3

drivers/char/hw_random/pseries-rng.c

+7 −4
Original line number Original line Diff line number Diff line
@@ -25,18 +25,21 @@ 
#include <asm/vio.h>

#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;

	int rc;





	rc = plpar_hcall(H_RANDOM, (unsigned long *)data);

	rc = plpar_hcall(H_RANDOM, (unsigned long *)buffer);

	if (rc != H_SUCCESS) {

	if (rc != H_SUCCESS) {

		pr_err_ratelimited("H_RANDOM call failed %d\n", rc);

		pr_err_ratelimited("H_RANDOM call failed %d\n", rc);

		return -EIO;

		return -EIO;

	}

	}

	memcpy(data, buffer, size);





	/* The hypervisor interface returns 64 bits */

	/* 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 = {

static struct hwrng pseries_rng = {

	.name		= KBUILD_MODNAME,

	.name		= KBUILD_MODNAME,

	.data_read	= pseries_rng_data_read,

	.read		= pseries_rng_read,

};

};





static int __init pseries_rng_probe(struct vio_dev *dev,

static int __init pseries_rng_probe(struct vio_dev *dev,