From 24c65bc7037e7d0f362c0df70d17dd72ee64b8b9 Mon Sep 17 00:00:00 2001 From: Greg Kurz Date: Fri, 31 Oct 2014 07:50:11 +0100 Subject: [PATCH] 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 d3cc7996473a7bdd33256029988ea690754e4e2a Author: Amit Shah 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 Signed-off-by: Herbert Xu --- 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 6226aa08c36a..bcf86f91800a 100644 --- a/drivers/char/hw_random/pseries-rng.c +++ b/drivers/char/hw_random/pseries-rng.c @@ -25,18 +25,21 @@ #include -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, -- 2.30.2