[ 25/82] hw_random: make buffer usable in scatterlist.

Ben Hutchings
2013-03-18T04:37:06Z

From: Rusty Russell <rusty@rustcorp.com.au>

commit f7f154f1246ccc5a0a7e9ce50932627d60a0c878 upstream.

virtio_rng feeds the randomness buffer handed by the core directly
into the scatterlist, since commit bb347d98079a547e80bd4722dee1de61e4dca0e8.

However, if CONFIG_HW_RANDOM=m, the static buffer isn't a linear address
(at least on most archs). We could fix this in virtio_rng, but it's actually
far easier to just do it in the core as virtio_rng would have to allocate
a buffer every time (it doesn't know how much the core will want to read).

Reported-by: Aurelien Jarno <aurelien@aurel32.net>
Tested-by: Aurelien Jarno <aurelien@aurel32.net>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
drivers/char/hw_random/core.c | 19 ++++++++++++++++---
1 file changed, 16 insertions(+), 3 deletions(-)

--- a/drivers/char/hw_random/core.c
+++ b/drivers/char/hw_random/core.c
@@ -40,6 +40,7 @@
#include <linux/init.h>
#include <linux/miscdevice.h>
#include <linux/delay.h>
+#include <linux/slab.h>
#include <asm/uaccess.h>

@@ -52,8 +53,12 @@ static struct hwrng *current_rng;
static LIST_HEAD(rng_list);
static DEFINE_MUTEX(rng_mutex);
static int data_avail;
-static u8 rng_buffer[SMP_CACHE_BYTES < 32 ? 32 : SMP_CACHE_BYTES]
- __cacheline_aligned;
+static u8 *rng_buffer;
+
+static size_t rng_buffer_size(void)
+{
+ return SMP_CACHE_BYTES < 32 ? 32 : SMP_CACHE_BYTES;
+}

static inline int hwrng_init(struct hwrng *rng)
{
@@ -116,7 +121,7 @@ static ssize_t rng_dev_read(struct file

if (!data_avail) {
bytes_read = rng_get_data(current_rng, rng_buffer,
- sizeof(rng_buffer),
+ rng_buffer_size(),
!(filp->f_flags & O_NONBLOCK));
if (bytes_read < 0) {
err = bytes_read;
@@ -307,6 +312,14 @@ int hwrng_register(struct hwrng *rng)

mutex_lock(&rng_mutex);

+ /* kmalloc makes this safe for virt_to_page() in virtio_rng.c */
+ err = -ENOMEM;
+ if (!rng_buffer) {
+ rng_buffer = kmalloc(rng_buffer_size(), GFP_KERNEL);
+ if (!rng_buffer)
+ goto out_unlock;
+ }
+
/* Must not register two RNGs with the same name. */
err = -EEXIST;
list_for_each_entry(tmp, &rng_list, list) {