Re: virtio-rng only returns zeros with CONFIG_HW_RANDOM=m

Rusty Russell
2013-05-30T05:34:32Z

Jens Axboe <axboe@kernel.dk> writes:
> On Wed, Feb 27 2013, Rusty Russell wrote:
>> Aurelien Jarno <aurelien@aurel32.net> 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 ;-).
>>
>> Wow. Fortunately, all of SLES, RHEL, Ubuntu or Fedora set
>> CONFIG_HW_RANDOM=y. What do they know that we don't?
>>
>> Oops, looks like Debian testing: config-3.2.0-4-amd64:CONFIG_HW_RANDOM=m
>>
>> > 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;
>>
>> Yuck... It would be nice if this has oopsed. Jens, what about this patch?
>>
>> Cheers,
>> Rusty.
>>
>> Subject: scatterlist: sg_set_buf() argument must be in linear mapping.
>>
>> Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
>>
>> diff --git a/include/linux/scatterlist.h b/include/linux/scatterlist.h
>> index 4bd6c06..9365375 100644
>> --- a/include/linux/scatterlist.h
>> +++ b/include/linux/scatterlist.h
>> @@ -111,6 +111,9 @@ static inline struct page *sg_page(struct scatterlist *sg)
>> static inline void sg_set_buf(struct scatterlist *sg, const void *buf,
>> unsigned int buflen)
>> {
>> +#ifdef CONFIG_DEBUG_SG
>> + BUG_ON(!virt_addr_valid(buf));
>> +#endif
>> sg_set_page(sg, virt_to_page(buf), buflen, offset_in_page(buf));
>> }
>
> Looks good to me, in lieu of being able to return an error. Want me to
> queue it up?
>
> --
> Jens Axboe

Ping? I haven't seen this go into Linus' tree...

Subject: scatterlist: sg_set_buf() argument must be in linear mapping.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

diff --git a/include/linux/scatterlist.h b/include/linux/scatterlist.h
index 4bd6c06..9365375 100644
--- a/include/linux/scatterlist.h
+++ b/include/linux/scatterlist.h
@@ -111,6 +111,9 @@ static inline struct page *sg_page(struct scatterlist *sg)
static inline void sg_set_buf(struct scatterlist *sg, const void *buf,
unsigned int buflen)
{
+#ifdef CONFIG_DEBUG_SG
+ BUG_ON(!virt_addr_valid(buf));
+#endif
sg_set_page(sg, virt_to_page(buf), buflen, offset_in_page(buf));
}