Aurelien Jarno <aurelien@xxxxxxxxxxx> writes: > Hi, > > I have noticed that virtio-rng only returns zero for kernels >= 2.6.33 > built with CONFIG_HW_RANDOM=m. This is a bit much too predictable for a > random generator ;-). > > The reason for that is virtio expects guest real addresses, while > rng_core.ko (ie when built as a module) is passing a vmalloced buffer > to the virtio-rng read function, declared as such: > > static u8 rng_buffer[SMP_CACHE_BYTES < 32 ? 32 : SMP_CACHE_BYTES] > __cacheline_aligned; > > This is basically the same issue than the following one: > > https://lists.linux-foundation.org/pipermail/virtualization/2008-May/010946.html > > but introduced in a more subtle way in this commit: > > commit bb347d98079a547e80bd4722dee1de61e4dca0e8 > Author: Ian Molton <ian.molton@xxxxxxxxxxxxxxx> > Date: Tue Dec 1 15:26:33 2009 +0800 OK, I looked at doing a kmalloc and copy in virtio_rng, but it's very inelegant (we don't know what size of buffer to allocate). No driver other than virtio_rng cares about this issue, but it's still far easier to fix in the core. How's this? Works here... Subject: 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@xxxxxxxxxxx> Signed-off-by: Rusty Russell <rusty@xxxxxxxxxxxxxxx> diff --git a/drivers/char/hw_random/core.c b/drivers/char/hw_random/core.c index 1bafb40..69ae597 100644 --- 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) { -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
