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Re: [Qemu-devel] [PATCH] VirtIO-RNG: Update default entropy source to `/
From: |
Richard W.M. Jones |
Subject: |
Re: [Qemu-devel] [PATCH] VirtIO-RNG: Update default entropy source to `/dev/urandom` |
Date: |
Fri, 3 May 2019 17:11:35 +0100 |
User-agent: |
Mutt/1.5.21 (2010-09-15) |
On Fri, May 03, 2019 at 05:46:13PM +0200, Kashyap Chamarthy wrote:
> When QEMU exposes a VirtIO-RNG device to the guest, that device needs a
> source of entropy, and that source needs to be "non-blocking", like
> `/dev/urandom`. However, currently QEMU defaults to the problematic
> `/dev/random`, which is "blocking" (as in, it waits until sufficient
> entropy is available).
>
> So change the entropy source to the recommended `/dev/urandom`.
>
> Related discussion in these[1][2] past threads.
>
> [1] https://lists.nongnu.org/archive/html/qemu-devel/2018-06/msg08335.html
> -- "RNG: Any reason QEMU doesn't default to `/dev/urandom`?"
> [2] https://lists.nongnu.org/archive/html/qemu-devel/2018-09/msg02724.html
> -- "[RFC] Virtio RNG: Consider changing the default entropy source to
> /dev/urandom"
>
> Signed-off-by: Kashyap Chamarthy <address@hidden>
> ---
> backends/rng-random.c | 2 +-
> qemu-options.hx | 2 +-
> 2 files changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/backends/rng-random.c b/backends/rng-random.c
> index e2a49b0571..eff36ef140 100644
> --- a/backends/rng-random.c
> +++ b/backends/rng-random.c
> @@ -112,7 +112,7 @@ static void rng_random_init(Object *obj)
> rng_random_set_filename,
> NULL);
>
> - s->filename = g_strdup("/dev/random");
> + s->filename = g_strdup("/dev/urandom");
> s->fd = -1;
> }
>
> diff --git a/qemu-options.hx b/qemu-options.hx
> index 51802cbb26..a525609149 100644
> --- a/qemu-options.hx
> +++ b/qemu-options.hx
> @@ -4276,7 +4276,7 @@ Creates a random number generator backend which obtains
> entropy from
> a device on the host. The @option{id} parameter is a unique ID that
> will be used to reference this entropy backend from the @option{virtio-rng}
> device. The @option{filename} parameter specifies which file to obtain
> -entropy from and if omitted defaults to @option{/dev/random}.
> +entropy from and if omitted defaults to @option{/dev/urandom}.
>
> @item -object rng-egd,address@hidden,address@hidden
I think this is a very sensible change, removing a bit of superstition
about randomness.
Reviewed-by: Richard W.M. Jones <address@hidden>
Rich.
--
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