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

[Rusty Russell <rusty@rustcorp.com.au>]

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));
 }