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

From: Andy Lutomirski
Date: Fri Oct 21 2016 - 17:04:53 EST

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 method -- has to allocate the
> recipient buffer in physically contiguous memory.

Indeed. This bug should be fixed by: