| Message ID | 20180913212551.2435-1-boris.ostrovsky@oracle.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [v2] tpm: Restore functionality to xen vtpm driver. | expand |
On Thu, Sep 13, 2018 at 05:25:51PM -0400, Boris Ostrovsky wrote: > From: "Dr. Greg Wettstein" <greg@wind.enjellic.com> > > Functionality of the xen-tpmfront driver was lost secondary to > the introduction of xenbus multi-page support in commit ccc9d90a9a8b > ("xenbus_client: Extend interface to support multi-page ring"). > > In this commit a pointer to the shared page address was being > passed to the xenbus_grant_ring() function rather then the > address of the shared page itself. This resulted in a situation I'm sorry but I'm far from being expert with Xen and this sentence confuses me so maybe could open it up a bit. For me "shared page address" and "address of the shared page" are the same thing. What am I missing? I mean just different forms in english to describe the exact same thing... /Jarkko
On 9/16/18 3:25 PM, Jarkko Sakkinen wrote: > On Thu, Sep 13, 2018 at 05:25:51PM -0400, Boris Ostrovsky wrote: >> From: "Dr. Greg Wettstein" <greg@wind.enjellic.com> >> >> Functionality of the xen-tpmfront driver was lost secondary to >> the introduction of xenbus multi-page support in commit ccc9d90a9a8b >> ("xenbus_client: Extend interface to support multi-page ring"). >> >> In this commit a pointer to the shared page address was being >> passed to the xenbus_grant_ring() function rather then the >> address of the shared page itself. This resulted in a situation > I'm sorry but I'm far from being expert with Xen and this sentence > confuses me so maybe could open it up a bit. > > For me "shared page address" and "address of the shared page" are > the same thing. What am I missing? I mean just different forms in > english to describe the exact same thing... xenbus_grant_ring() takes as an argument address of the ring shared between two guests. What Greg was trying to describe was the fact that existing code instead passes address of location where this address is stored (i.e. somewhat similar to difference between pointer and pointer to a pointer). Would this be better: "In this commit pointer to location of the where the shared page address is stored was being passed to the xenbus_grant_ring() function rather then the address of the shared page itself." Or please suggest a better alternative, I'll be happy to amend the commit message. Thanks. -boris
On Mon, Sep 17, 2018 at 09:54:37AM -0400, Boris Ostrovsky wrote: > On 9/16/18 3:25 PM, Jarkko Sakkinen wrote: > > On Thu, Sep 13, 2018 at 05:25:51PM -0400, Boris Ostrovsky wrote: > >> From: "Dr. Greg Wettstein" <greg@wind.enjellic.com> > >> > >> Functionality of the xen-tpmfront driver was lost secondary to > >> the introduction of xenbus multi-page support in commit ccc9d90a9a8b > >> ("xenbus_client: Extend interface to support multi-page ring"). > >> > >> In this commit a pointer to the shared page address was being > >> passed to the xenbus_grant_ring() function rather then the > >> address of the shared page itself. This resulted in a situation > > I'm sorry but I'm far from being expert with Xen and this sentence > > confuses me so maybe could open it up a bit. > > > > For me "shared page address" and "address of the shared page" are > > the same thing. What am I missing? I mean just different forms in > > english to describe the exact same thing... > > xenbus_grant_ring() takes as an argument address of the ring shared > between two guests. What Greg was trying to describe was the fact that > existing code instead passes address of location where this address is > stored (i.e. somewhat similar to difference between pointer and pointer > to a pointer). Just to understand this bug better why did not the wrong version cause any undefined behavior? Sounds like a fatal bug. Does this cause crashes? > Would this be better: > > "In this commit pointer to location of the where the shared page address > is stored was being passed to the xenbus_grant_ring() function rather > then the > address of the shared page itself." Yes, definitely! > Or please suggest a better alternative, I'll be happy to amend the > commit message. Thank you. > Thanks. > -boris /Jarkko
On 9/17/18 5:19 PM, Jarkko Sakkinen wrote: > On Mon, Sep 17, 2018 at 09:54:37AM -0400, Boris Ostrovsky wrote: >> On 9/16/18 3:25 PM, Jarkko Sakkinen wrote: >>> On Thu, Sep 13, 2018 at 05:25:51PM -0400, Boris Ostrovsky wrote: >>>> From: "Dr. Greg Wettstein" <greg@wind.enjellic.com> >>>> >>>> Functionality of the xen-tpmfront driver was lost secondary to >>>> the introduction of xenbus multi-page support in commit ccc9d90a9a8b >>>> ("xenbus_client: Extend interface to support multi-page ring"). >>>> >>>> In this commit a pointer to the shared page address was being >>>> passed to the xenbus_grant_ring() function rather then the >>>> address of the shared page itself. This resulted in a situation >>> I'm sorry but I'm far from being expert with Xen and this sentence >>> confuses me so maybe could open it up a bit. >>> >>> For me "shared page address" and "address of the shared page" are >>> the same thing. What am I missing? I mean just different forms in >>> english to describe the exact same thing... >> xenbus_grant_ring() takes as an argument address of the ring shared >> between two guests. What Greg was trying to describe was the fact that >> existing code instead passes address of location where this address is >> stored (i.e. somewhat similar to difference between pointer and pointer >> to a pointer). > Just to understand this bug better why did not the wrong version > cause any undefined behavior? Sounds like a fatal bug. Does this > cause crashes? AFAIK, no, no crashes. I haven't tested this myself (and I believe relatively few people use this functionality, which explains why this has not been fixed for so long) but I don't think it will necessarily crash. It's just that the frontend driver will be reading from wrong location, causing TPM not to function properly. Or maybe the frontend is writing but then I believe the write would occur into tpm_private, and so will corrupt it. But the protocol will fail right after this anyway. > >> Would this be better: >> >> "In this commit pointer to location of the where the shared page address >> is stored was being passed to the xenbus_grant_ring() function rather >> then the >> address of the shared page itself." > Yes, definitely! OK, I'll send it shortly. Thanks. -boris > >> Or please suggest a better alternative, I'll be happy to amend the >> commit message. > Thank you. > >> Thanks. >> -boris > /Jarkko
On tisdag 18 september 2018 kl. 01:25:29 EEST Boris Ostrovsky wrote: > On 9/17/18 5:19 PM, Jarkko Sakkinen wrote: > > Just to understand this bug better why did not the wrong version > > cause any undefined behavior? Sounds like a fatal bug. Does this > > cause crashes? > > AFAIK, no, no crashes. I haven't tested this myself (and I believe > relatively few people use this functionality, which explains why this > has not been fixed for so long) but I don't think it will necessarily > crash. It's just that the frontend driver will be reading from wrong > location, causing TPM not to function properly. I bumped my head into this last week and spent most of the week trying to figure out why the vtpm did not respond. Finally found the email from the guy that dirscovered and fixed it. Did the fix and rescompiled. Now it seems to be working fine. The patch is surprisingly 2 years old!! I will be very pleased to see it go in to the official kernel! But no crash. Just a timeout when trying to communicate with the vtpm-engine. Best Dag
diff --git a/drivers/char/tpm/xen-tpmfront.c b/drivers/char/tpm/xen-tpmfront.c index 911475d36800..b150f87f38f5 100644 --- a/drivers/char/tpm/xen-tpmfront.c +++ b/drivers/char/tpm/xen-tpmfront.c @@ -264,7 +264,7 @@ static int setup_ring(struct xenbus_device *dev, struct tpm_private *priv) return -ENOMEM; } - rv = xenbus_grant_ring(dev, &priv->shr, 1, &gref); + rv = xenbus_grant_ring(dev, priv->shr, 1, &gref); if (rv < 0) return rv;