From: Andres Beltran <lkmlab...@gmail.com> Sent: Monday, June 29, 2020 2:51 PM > > On Mon, Jun 29, 2020 at 4:46 PM Wei Liu <wei....@kernel.org> wrote: > > > > On Mon, Jun 29, 2020 at 04:02:25PM -0400, Andres Beltran wrote: > > > Currently, VMbus drivers use pointers into guest memory as request IDs > > > for interactions with Hyper-V. To be more robust in the face of errors > > > or malicious behavior from a compromised Hyper-V, avoid exposing > > > guest memory addresses to Hyper-V. Also avoid Hyper-V giving back a > > > bad request ID that is then treated as the address of a guest data > > > structure with no validation. Instead, encapsulate these memory > > > addresses and provide small integers as request IDs. > > > > > > Signed-off-by: Andres Beltran <lkmlab...@gmail.com> > > > --- > > > Changes in v2: > > > - Get rid of "rqstor" variable in __vmbus_open(). > > > > > > drivers/hv/channel.c | 146 +++++++++++++++++++++++++++++++++++++++++ > > > include/linux/hyperv.h | 21 ++++++ > > > 2 files changed, 167 insertions(+) > > > > > > diff --git a/drivers/hv/channel.c b/drivers/hv/channel.c > > > index 3ebda7707e46..c89d57d0c2d2 100644 > > > --- a/drivers/hv/channel.c > > > +++ b/drivers/hv/channel.c > > > @@ -112,6 +112,70 @@ int vmbus_alloc_ring(struct vmbus_channel > > > *newchannel, > > > } > > > EXPORT_SYMBOL_GPL(vmbus_alloc_ring); > > > > > > +/** > > > + * request_arr_init - Allocates memory for the requestor array. Each slot > > > + * keeps track of the next available slot in the array. Initially, each > > > + * slot points to the next one (as in a Linked List). The last slot > > > + * does not point to anything, so its value is U64_MAX by default. > > > + * @size The size of the array > > > + */ > > > +static u64 *request_arr_init(u32 size) > > > +{ > > > + int i; > > > + u64 *req_arr; > > > + > > > + req_arr = kcalloc(size, sizeof(u64), GFP_KERNEL); > > > + if (!req_arr) > > > + return NULL; > > > + > > > + for (i = 0; i < size - 1; i++) > > > + req_arr[i] = i + 1; > > > + > > > + /* Last slot (no more available slots) */ > > > + req_arr[i] = U64_MAX; > > > + > > > + return req_arr; > > > +} > > > + > > > +/* > > > + * vmbus_alloc_requestor - Initializes @rqstor's fields. > > > + * Slot at index 0 is the first free slot. > > > + * @size: Size of the requestor array > > > + */ > > > +static int vmbus_alloc_requestor(struct vmbus_requestor *rqstor, u32 > > > size) > > > +{ > > > + u64 *rqst_arr; > > > + unsigned long *bitmap; > > > + > > > + rqst_arr = request_arr_init(size); > > > + if (!rqst_arr) > > > + return -ENOMEM; > > > + > > > + bitmap = bitmap_zalloc(size, GFP_KERNEL); > > > + if (!bitmap) { > > > + kfree(rqst_arr); > > > + return -ENOMEM; > > > + } > > > + > > > + rqstor->req_arr = rqst_arr; > > > + rqstor->req_bitmap = bitmap; > > > + rqstor->size = size; > > > + rqstor->next_request_id = 0; > > > + spin_lock_init(&rqstor->req_lock); > > > + > > > + return 0; > > > +} > > > + > > > +/* > > > + * vmbus_free_requestor - Frees memory allocated for @rqstor > > > + * @rqstor: Pointer to the requestor struct > > > + */ > > > +static void vmbus_free_requestor(struct vmbus_requestor *rqstor) > > > +{ > > > + kfree(rqstor->req_arr); > > > + bitmap_free(rqstor->req_bitmap); > > > +} > > > + > > > static int __vmbus_open(struct vmbus_channel *newchannel, > > > void *userdata, u32 userdatalen, > > > void (*onchannelcallback)(void *context), void > > > *context) > > > @@ -132,6 +196,12 @@ static int __vmbus_open(struct vmbus_channel > > > *newchannel, > > > if (newchannel->state != CHANNEL_OPEN_STATE) > > > return -EINVAL; > > > > > > + /* Create and init requestor */ > > > + if (newchannel->rqstor_size) { > > > + if (vmbus_alloc_requestor(&newchannel->requestor, > > > newchannel- > >rqstor_size)) > > > + return -ENOMEM; > > > + } > > > + > > > > Sorry for not noticing this in the last round: this infrastructure is > > initialized conditionally but used unconditionally. > > > > I can think of two options here: > > > > 1. Mandate rqstor_size to be non-zero. Always initialize this > > infra. > > 2. Modify vmbus_next_request_id and vmbus_request_addr to deal with > > uninitialized state. > > > > For #2, you can simply check rqstor->size _before_ taking the lock > > (because it may be uninitialized, and the assumption is ->size will not > > change during the channel's lifetime, hence no lock is needed) and > > simply return the same value to the caller. > > > > Wei. > > Right. I think option #2 would be preferable in this case, because #1 works > if we had a default non-zero size for cases where rqstor_size has not been > set to a non-zero value before calling vmbus_alloc_requestor(). For #2, what > do you mean by "same value"? I think we would need to return > VMBUS_RQST_ERROR if the size is 0, because otherwise we would be > returning the same guest memory address which we don't want to expose. >
I'm not understanding the problem here. Any VMbus driver that uses this requestID allocation mechanism must set newchannel->rqstor_size to a non-zero value. But if a VMbus driver doesn't use the mechanism, then newchannel->rqstor_size will default to zero, and the mechanism will not be initialized for the channels used by that driver. I think the cleanup of the mechanism handles the case where it wasn't ever initialized. Or am I missing something? Michael