On Fri, 31 Oct 2014 18:00:12 +1100
Michael Ellerman <m...@ellerman.id.au> wrote:
> On Fri, 2014-10-31 at 07:50 +0100, Greg Kurz wrote:
> > The add_early_randomness() function in drivers/char/hw_random/core.c passes
> > a 16-byte buffer to pseries_rng_data_read(). Unfortunately, plpar_hcall()
> > returns four 64-bit values and trashes 16 bytes on the stack.
>
> Hmm, thanks. I thought I'd fixed that, but I guess I never sent the patch :}
>
Heh so many patches ! :)
> > This bug has been lying around for a long time. It got unveiled by:
> >
> > commit d3cc7996473a7bdd33256029988ea690754e4e2a
> > Author: Amit Shah <amit.s...@redhat.com>
> > Date: Thu Jul 10 15:42:34 2014 +0530
> >
> > hwrng: fetch randomness only after device init
> >
> > It may trig a oops while loading or unloading the pseries-rng module for
> > both
> > PowerVM and PowerKVM guests.
> >
> > This patch does two things:
> > - pass an intermediate well sized buffer to plpar_hcall(). This is
> > acceptalbe
> > since we're not on a hot path.
>
> Well probably, can you do a before and after test of dd if=/dev/hwrng ?
>
I had to do this to be able to run the before test:
@@ -78,7 +78,7 @@ static size_t rng_buffer_size(void)
static void add_early_randomness(struct hwrng *rng)
{
- unsigned char bytes[16];
+ unsigned char bytes[32];
I ran tests for 128 MB and 1G several times in a PowerKVM guest on a POWER8 box.
Before:
[root@fedora20-ppc64 ~]# time dd if=/dev/hwrng of=/dev/null bs=1024 count=131072
131072+0 records in
131072+0 records out
134217728 bytes (134 MB) copied, 17.0503 s, 7.9 MB/s
real 0m17.051s
user 0m0.024s
sys 0m16.797s
[root@fedora20-ppc64 ~]# time dd if=/dev/hwrng of=/dev/null bs=1024
count=1048576
1048576+0 records in
1048576+0 records out
1073741824 bytes (1.1 GB) copied, 136.374 s, 7.9 MB/s
real 2m16.376s
user 0m0.189s
sys 2m14.367s
After:
[root@fedora20-ppc64 ~]# time dd if=/dev/hwrng of=/dev/null bs=1024 count=131072
131072+0 records in
131072+0 records out
134217728 bytes (134 MB) copied, 17.0502 s, 7.9 MB/s
real 0m17.051s
user 0m0.024s
sys 0m16.797s
[root@fedora20-ppc64 ~]# time dd if=/dev/hwrng of=/dev/null bs=1024
count=1048576
1048576+0 records in
1048576+0 records out
1073741824 bytes (1.1 GB) copied, 136.432 s, 7.9 MB/s
real 2m16.433s
user 0m0.188s
sys 2m14.370s
It shows no degradation of performance.
> > Cc'ing stable as I could reproduce back to 3.15.10
>
> The right way to CC stable for a patch that isn't yet in upstream is to add:
>
> CC: sta...@vger.kernel.org
>
> Before your Signed-off-by. They will then pick it up once it's merged into
> Linus' tree. See Documentation/stable_kernel_rules.txt
>
> cheers
>
Oops... should I repost then ?
Thanks.
--
Greg
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