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Date: Fri, 26 Jun 2020 13:19:49 +0000
From: Wei Liu <wei.liu@...nel.org>
To: Andres Beltran <lkmlabelt@...il.com>
Cc: kys@...rosoft.com, haiyangz@...rosoft.com, sthemmin@...rosoft.com,
wei.liu@...nel.org, linux-hyperv@...r.kernel.org,
linux-kernel@...r.kernel.org, mikelley@...rosoft.com,
parri.andrea@...il.com
Subject: Re: [PATCH 1/3] Drivers: hv: vmbus: Add vmbus_requestor data
structure for VMBus hardening
On Thu, Jun 25, 2020 at 11:37:21AM -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 <lkmlabelt@...il.com>
> ---
> 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);
You can simply use err here to store the return value or even get rid of
rqstor by doing
if (vmbus_alloc_requestor(...))
> + 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);
Do you really need the irqsave variant here? I.e. is there really a
chance this code is reachable from an interrupt handler?
Wei.
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