Re: [PATCH RESEND] hwrng: core - don't pass stack allocated buffer to rng->read()

[Andy Lutomirski]

On Fri, Oct 21, 2016 at 1:48 PM, Laszlo Ersek <lersek@xxxxxxxxxx> wrote:
> The virtio-rng backend for hwrng passes the buffer that it receives for
> filling to sg_set_buf() directly, in:
>
> virtio_read()       [drivers/char/hw_random/virtio-rng.c]
>   register_buffer() [drivers/char/hw_random/virtio-rng.c]
>     sg_init_one()   [lib/scatterlist.c]
>       sg_set_buf()  [include/linux/scatterlist.h]
>
> In turn, the sg_set_buf() function, when built with CONFIG_DEBUG_SG,
> actively enforces (justifiedly) that the buffer used within the
> scatter-gather list live in physically contiguous memory:
>
>   BUG_ON(!virt_addr_valid(buf));
>
> The combination of the above two facts means that whatever calls
> virtio_read() -- via the hwrng.read() method -- has to allocate the
> recipient buffer in physically contiguous memory.

Indeed.  This bug should be fixed by:

https://git.kernel.org/cgit/linux/kernel/git/herbert/cryptodev-2.6.git/commit/?id=6d4952d9d9d4dc2bb9c0255d95a09405a1e958f7