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 <lkmlabelt@xxxxxxxxx> --- drivers/hv/channel.c | 149 +++++++++++++++++++++++++++++++++++++++++ include/linux/hyperv.h | 21 ++++++ 2 files changed, 170 insertions(+) diff --git a/drivers/hv/channel.c b/drivers/hv/channel.c index 3ebda7707e46..2ea1bfecbfda 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) @@ -122,6 +186,7 @@ static int __vmbus_open(struct vmbus_channel *newchannel, u32 send_pages, recv_pages; unsigned long flags; int err; + int rqstor; if (userdatalen > MAX_USER_DEFINED_BYTES) return -EINVAL; @@ -132,6 +197,14 @@ static int __vmbus_open(struct vmbus_channel *newchannel, if (newchannel->state != CHANNEL_OPEN_STATE) return -EINVAL; + /* Create and init requestor */ + if (newchannel->rqstor_size) { + rqstor = vmbus_alloc_requestor(&newchannel->requestor, + newchannel->rqstor_size); + if (rqstor) + return -ENOMEM; + } + newchannel->state = CHANNEL_OPENING_STATE; newchannel->onchannel_callback = onchannelcallback; newchannel->channel_callback_context = context; @@ -228,6 +301,7 @@ static int __vmbus_open(struct vmbus_channel *newchannel, error_clean_ring: hv_ringbuffer_cleanup(&newchannel->outbound); hv_ringbuffer_cleanup(&newchannel->inbound); + vmbus_free_requestor(&newchannel->requestor); newchannel->state = CHANNEL_OPEN_STATE; return err; } @@ -703,6 +777,9 @@ static int vmbus_close_internal(struct vmbus_channel *channel) channel->ringbuffer_gpadlhandle = 0; } + if (!ret) + vmbus_free_requestor(&channel->requestor); + return ret; } @@ -937,3 +1014,75 @@ int vmbus_recvpacket_raw(struct vmbus_channel *channel, void *buffer, buffer_actual_len, requestid, true); } EXPORT_SYMBOL_GPL(vmbus_recvpacket_raw); + +/* + * vmbus_next_request_id - Returns a new request id. It is also + * the index at which the guest memory address is stored. + * Uses a spin lock to avoid race conditions. + * @rqstor: Pointer to the requestor struct + * @rqst_add: Guest memory address to be stored in the array + */ +u64 vmbus_next_request_id(struct vmbus_requestor *rqstor, u64 rqst_addr) +{ + unsigned long flags; + u64 current_id; + + spin_lock_irqsave(&rqstor->req_lock, flags); + current_id = rqstor->next_request_id; + + /* Requestor array is full */ + if (current_id >= rqstor->size) { + current_id = VMBUS_RQST_ERROR; + goto exit; + } + + rqstor->next_request_id = rqstor->req_arr[current_id]; + rqstor->req_arr[current_id] = rqst_addr; + + /* The already held spin lock provides atomicity */ + bitmap_set(rqstor->req_bitmap, current_id, 1); + +exit: + spin_unlock_irqrestore(&rqstor->req_lock, flags); + return current_id; +} +EXPORT_SYMBOL_GPL(vmbus_next_request_id); + +/* + * vmbus_request_addr - Returns the memory address stored at @trans_id + * in @rqstor. Uses a spin lock to avoid race conditions. + * @rqstor: Pointer to the requestor struct + * @trans_id: Request id sent back from Hyper-V. Becomes the requestor's + * next request id. + */ +u64 vmbus_request_addr(struct vmbus_requestor *rqstor, u64 trans_id) +{ + unsigned long flags; + u64 req_addr; + + spin_lock_irqsave(&rqstor->req_lock, flags); + + /* Invalid trans_id */ + if (trans_id >= rqstor->size) { + req_addr = VMBUS_RQST_ERROR; + goto exit; + } + + /* Invalid trans_id: empty slot */ + if (!test_bit(trans_id, rqstor->req_bitmap)) { + req_addr = VMBUS_RQST_ERROR; + goto exit; + } + + req_addr = rqstor->req_arr[trans_id]; + rqstor->req_arr[trans_id] = rqstor->next_request_id; + rqstor->next_request_id = trans_id; + + /* The already held spin lock provides atomicity */ + bitmap_clear(rqstor->req_bitmap, trans_id, 1); + +exit: + spin_unlock_irqrestore(&rqstor->req_lock, flags); + return req_addr; +} +EXPORT_SYMBOL_GPL(vmbus_request_addr); diff --git a/include/linux/hyperv.h b/include/linux/hyperv.h index 38100e80360a..c509d20ab7db 100644 --- a/include/linux/hyperv.h +++ b/include/linux/hyperv.h @@ -716,6 +716,21 @@ enum vmbus_device_type { HV_UNKNOWN, }; +/* + * Provides request ids for VMBus. Encapsulates guest memory + * addresses and stores the next available slot in req_arr + * to generate new ids in constant time. + */ +struct vmbus_requestor { + u64 *req_arr; + unsigned long *req_bitmap; /* is a given slot available? */ + u32 size; + u64 next_request_id; + spinlock_t req_lock; /* provides atomicity */ +}; + +#define VMBUS_RQST_ERROR U64_MAX + struct vmbus_device { u16 dev_type; guid_t guid; @@ -940,8 +955,14 @@ struct vmbus_channel { u32 fuzz_testing_interrupt_delay; u32 fuzz_testing_message_delay; + /* request/transaction ids for VMBus */ + struct vmbus_requestor requestor; + u32 rqstor_size; }; +u64 vmbus_next_request_id(struct vmbus_requestor *rqstor, u64 rqst_addr); +u64 vmbus_request_addr(struct vmbus_requestor *rqstor, u64 trans_id); + static inline bool is_hvsock_channel(const struct vmbus_channel *c) { return !!(c->offermsg.offer.chn_flags & -- 2.25.1