hw_random: make buffer usable in scatterlist.

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>
Cc: stable@kernel.org

diff --git a/drivers/char/hw_random/core.c b/drivers/char/hw_random/core.c
index 1bafb40ec8a213480f355b480819f092fdfebd08..69ae5972713cf814e968c3c9d9ad8743d3dd240d 100644 (file)
--- 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 *filp, char __user *buf,
 
                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) {