[3.16.y-ckt stable] Patch "hwrng: pseries - port to new read API and fix stack corruption" has been added to staging queue

[Luis Henriques]

This is a note to let you know that I have just added a patch titled

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

to the linux-3.16.y-queue branch of the 3.16.y-ckt extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.16.y-queue

This patch is scheduled to be released in version 3.16.7-ckt2.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.16.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From fe1319fa98843e380521e2b97931aad314f7def5 Mon Sep 17 00:00:00 2001
From: Greg Kurz <gkurz at linux.vnet.ibm.com>
Date: Fri, 31 Oct 2014 07:50:11 +0100
Subject: hwrng: pseries - port to new read API and fix stack corruption

commit 24c65bc7037e7d0f362c0df70d17dd72ee64b8b9 upstream.

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 d3cc7996473a7bdd33256029988ea690754e4e2a
Author: Amit Shah <amit.shah at 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.

Signed-off-by: Greg Kurz <gkurz at linux.vnet.ibm.com>
Signed-off-by: Herbert Xu <herbert at gondor.apana.org.au>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 drivers/char/hw_random/pseries-rng.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/drivers/char/hw_random/pseries-rng.c b/drivers/char/hw_random/pseries-rng.c
index ab7ffdec0ec3..f38f2c13e79c 100644
--- a/drivers/char/hw_random/pseries-rng.c
+++ b/drivers/char/hw_random/pseries-rng.c
@@ -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,
--
2.1.0