On Wed, Jul 02, 2014 at 06:56:35PM +0530, Amit Shah wrote:
> Hi Jason,
>
> On (Wed) 02 Jul 2014 [13:00:19], Jason Cooper wrote:
> > Commit d9e7972619334 "hwrng: add randomness to system from rng sources"
> > added a call to rng_get_data() from the hwrng_register() function.
> > However, some rng devices need initialization before data can be read
> > from them.
> >
> > Also, the virtio-rng device does not behave properly when this call is
> > made in its probe() routine - the virtio core sets the DRIVER_OK status
> > bit only on a successful probe, which means the host ignores all
> > communication from the guest, and the guest insmod or boot process just
> > sits there doing nothing.
> >
> > [ jac: Modify the API to allow drivers to disable reading at probe, new
> > patch, copied Amit's commit message. ]
> >
> > CC: Kees Cook <keescook@xxxxxxxxxxxx>
> > CC: Jason Cooper <jason@xxxxxxxxxxxxxx>
> > CC: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>
> > CC: <stable@xxxxxxxxxxxxxxx> # v3.15+
> > Signed-off-by: Amit Shah <amit.shah@xxxxxxxxxx>
> > Signed-off-by: Jason Cooper <jason@xxxxxxxxxxxxxx>
> > ---
> > drivers/char/hw_random/core.c | 8 +++++---
> > include/linux/hw_random.h | 4 ++++
> > 2 files changed, 9 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/char/hw_random/core.c b/drivers/char/hw_random/core.c
> > index 334601cc81cf..b7b6c48ca682 100644
> > --- a/drivers/char/hw_random/core.c
> > +++ b/drivers/char/hw_random/core.c
> > @@ -347,9 +347,11 @@ int hwrng_register(struct hwrng *rng)
> > INIT_LIST_HEAD(&rng->list);
> > list_add_tail(&rng->list, &rng_list);
> >
> > - bytes_read = rng_get_data(rng, bytes, sizeof(bytes), 1);
> > - if (bytes_read > 0)
> > - add_device_randomness(bytes, bytes_read);
> > + if (!(rng->flags & HWRNG_NO_READ_AT_PROBE)) {
> > + bytes_read = rng_get_data(rng, bytes, sizeof(bytes), 1);
> > + if (bytes_read > 0)
> > + add_device_randomness(bytes, bytes_read);
> > + }
>
> But this has the inverse problem: if there are two hwrngs in the
> system, one will be initialized and probed. The other will not be
> initialized, but still be probed.
That's a problem outside the scope of this patch. You're basically
saying the ->init() should be called unconditionally for each hwrng. If
that's what driver authors assumed, that's not what is happening if
there is more than one driver in the system.
I think you should be changing the code a few lines up to make sure
hwrng_init() is called once for each driver.
> My version was more conservative while this one keeps the bug from the
> current kernels.
Huh? What do you mean by "keeps the bug from the current kernels." ?
Besides, you're second patch isn't actually doing any ->init to get the
hwrng ready for reading... If you had a real ->init function, and it
was always called, would rng_get_data() work at probe time for your
driver?
confused,
Jason.
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