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    Subject[ 030/100] hw_random: make buffer usable in scatterlist.
    Date
    3.8-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    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: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    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) {



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