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

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Message-ID: <CALCETrUUBJT81Yxm7f19kX+dbyqx9skYEVjYMzMx4zm-vGWWXQ@mail.gmail.com>
Date:   Fri, 21 Oct 2016 14:04:27 -0700
From:   Andy Lutomirski <luto@...capital.net>
To:     Laszlo Ersek <lersek@...hat.com>
Cc:     linux-crypto@...r.kernel.org,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Richard W.M. Jones" <rjones@...hat.com>,
        stable <stable@...r.kernel.org>,
        Amit Shah <amit.shah@...hat.com>,
        Andy Lutomirski <luto@...nel.org>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Kees Cook <keescook@...omium.org>,
        Matt Mackall <mpm@...enic.com>
Subject: Re: [PATCH RESEND] hwrng: core - don't pass stack allocated buffer to rng->read()

On Fri, Oct 21, 2016 at 1:48 PM, Laszlo Ersek <lersek@...hat.com> 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