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diff --git a/virtio-rpmb.tex b/virtio-rpmb.tex new file mode 100644 index 0000000..dfecc3c --- /dev/null +++ b/virtio-rpmb.tex @@ -0,0 +1,288 @@ +\section{RPMB Device}\label{sec:Device Types / RPMB Device} + +virtio-rpmb is a virtio based RPMB (Replay Protected Memory Block) +device. It is used as a tamper-resistant and anti-replay storage. +The device is driven via requests including read, write, get write +counter and program key, which are submitted via a request queue. +This section relies on definitions from paragraph 6.6.22 of +\hyperref[intro:eMMC]{eMMC}. +\subsection{Device ID}\label{sec:Device Types / RPMB Device / Device ID} + +28 + +\subsection{Virtqueues}\label{sec:Device Types / RPMB Device / Virtqueues} + +\begin{description} +\item[0] requestq +\end{description} + +\subsection{Feature bits}\label{sec:Device Types / RPMB Device / Feature bits} + +None. + +\subsection{Device configuration layout}\label{sec:Device Types / RPMB Device / Device configuration layout} + +All fields of this configuration are always available and read-only for the driver. + +\begin{lstlisting} +struct virtio_rpmb_config { + u8 capacity; + u8 max_wr_cnt; + u8 max_rd_cnt; +} +\end{lstlisting} + +\begin{description} +\item[\field{capacity}] is the capacity of the device (expressed in 128KB units). + The values MUST range between 0x00 and 0x80 inclusive. +\item[\field{max_wr_cnt and max_rd_cnt}] are the maximum numbers of RPMB + block count (256B) that can be performed to device in one request. 0 implies + no limitation. +\end{description} + +\devicenormative{\subsection}{Device Initialization}{Device Types / RPMB Device / Device Initialization} + +\begin{enumerate} +\item The virtqueue is initialized. +\item The device capacity MUST be initialized to a multiple of 128Kbytes and up to + 16Mbytes. +\end{enumerate} + +\subsection{Device Operation}\label{sec:Device Types / RPMB Device / Device Operation} + +The operation of a virtio RPMB device is driven by the requests placed on the virtqueue. + The type of request can be program key (VIRTIO_RPMB_REQ_PROGRAM_KEY), + get write counter (VIRTIO_RPMB_REQ_GET_WRITE_COUNTER), + write (VIRTIO_RPMB_REQ_DATA_WRITE), and read (VIRTIO_RPMB_REQ_DATA_READ). + A program key or write request can also combine with a + result read (VIRTIO_RPMB_REQ_RESULT_READ) for a returned result. + +\begin{lstlisting} +/* RPMB Request Types */ +#define VIRTIO_RPMB_REQ_PROGRAM_KEY 0x0001 +#define VIRTIO_RPMB_REQ_GET_WRITE_COUNTER 0x0002 +#define VIRTIO_RPMB_REQ_DATA_WRITE 0x0003 +#define VIRTIO_RPMB_REQ_DATA_READ 0x0004 +#define VIRTIO_RPMB_REQ_RESULT_READ 0x0005 + +/* RPMB Response Types */ +#define VIRTIO_RPMB_RESP_PROGRAM_KEY 0x0100 +#define VIRTIO_RPMB_RESP_GET_COUNTER 0x0200 +#define VIRTIO_RPMB_RESP_DATA_WRITE 0x0300 +#define VIRTIO_RPMB_RESP_DATA_READ 0x0400 +\end{lstlisting} + +\begin{description} +\item[\field{VIRTIO_RPMB_REQ_PROGRAM_KEY}] requests for authentication key programming. + If VIRTIO_RPMB_REQ_RESULT_READ is requested, the device returns the RPMB frame with + the response (VIRTIO_RPMB_RESP_PROGRAM_KEY), the calculated MAC and the result. + +\item[\field{VIRTIO_RPMB_REQ_GET_WRITE_COUNTER}] requests for reading the write counter. + The device returns the RPMB frame with the response (VIRTIO_RPMB_RESP_GET_COUNTER), + the writer counter, a copy of the nonce received in the request, the calculated + MAC and the result. + +\item[\field{VIRTIO_RPMB_REQ_DATA_WRITE}] requests for authenticated data write. + If VIRTIO_RPMB_REQ_RESULT_READ is requested, the device returns the RPMB data + frame with the response (VIRTIO_RPMB_RESP_DATA_WRITE), the incremented counter value, + the data address, the calculated MAC and the result. + +\item[\field{VIRTIO_RPMB_REQ_DATA_READ}] requests for authenticated data read. + The device returns the RPMB frame with the response (VIRTIO_RPMB_RESP_DATA_READ), + the block count, a copy of the nonce received in the request, the address, + the data, the calculated MAC and the result. + +\item[\field{VIRTIO_RPMB_REQ_RESULT_READ}] requests for a returned result. + It is used following with VIRTIO_RPMB_REQ_PROGRAM_KEY or VIRTIO_RPMB_REQ_DATA_WRITE + request types for a returned result in one or multiple RPMB frames. If it's not + requested, the device will not return result frame to the driver. +\end{description} + + +\subsubsection{Device Operation: Request Queue}\label{sec:Device Types / RPMB Device / Device Operation / Device Operation: Request Queue} + +The request information is delivered in RPMB frame. +The frame is in size of 512B. + +\begin{lstlisting} +struct virtio_rpmb_frame { + u8 stuff[196]; + u8 key_mac[32]; + u8 data[256]; + u8 nonce[16]; + be32 write_counter; + be16 address; + be16 block_count; + be16 result; + be16 req_resp; +}; + +/* RPMB Operation Results */ +#define VIRTIO_RPMB_RES_OK 0x0000 +#define VIRTIO_RPMB_RES_GENERAL_FAILURE 0x0001 +#define VIRTIO_RPMB_RES_AUTH_FAILURE 0x0002 +#define VIRTIO_RPMB_RES_COUNT_FAILURE 0x0003 +#define VIRTIO_RPMB_RES_ADDR_FAILURE 0x0004 +#define VIRTIO_RPMB_RES_WRITE_FAILURE 0x0005 +#define VIRTIO_RPMB_RES_READ_FAILURE 0x0006 +#define VIRTIO_RPMB_RES_NO_AUTH_KEY 0x0007 +#define VIRTIO_RPMB_RES_WRITE_COUNTER_EXPIRED 0x0080 +\end{lstlisting} + +\begin{description} +\item[\field{stuff}] Padding for the frame. + +\item[\field{key_mac}] is the authentication key or the message + authentication code (MAC) depending on the request/response type. + If the request is VIRTIO_RPMB_REQ_PROGRAM_KEY, it's used as an + authentication key. Otherwise, it's used as MAC. The MAC is calculated + using HMAC SHA-256. It takes as input a key and a message. The key + used for the MAC calculation is always the 256-bit RPMB authentication + key. The message used as input to the MAC calculation is the + concatenation of the fields in the RPMB frames excluding stuff bytes + and the MAC itself. + +\item[\field{data}] is used to be written or read via authenticated + read/write access. It's fixed 256B. + +\item[\field{nonce}] is a random number generated by the user for the read + or get write counter requests and copied to the response by the device. + It's used for anti-replay protection. + +\item[\field{writer_counter}] is the counter value for the total amount of + the successful authenticated data write requests. + +\item[\field{address}] is the address of the data to be written to or read + from the RPMB virtio device. It is the number of the accessed + half sector (256B). + +\item[\field{block_count}] is the number of blocks (256B) requested to be + read/written. It's limited by \field{max_wr_cnt} or \field{max_rd_cnt}. + For RPMB read request, one virtio buffer including request command and + the subsequent [\field{block_count}] virtio buffers for response data + are placed in the queue. + For RPMB write request, [\field{block_count}] virtio buffers including + request command and data are placed in the queue. + +\item[\field{result}] includes information about the status of access made + to the device. It is written by the device. + +\item[\field{req_resp}] is the type of request or response, to/from the device. +\end{description} + +\devicenormative{\paragraph}{Device Operation: Program Key}{Device Types / RPMB Device / Device Operation / Device Operation: Program Key} + +If VIRTIO_RPMB_REQ_RESULT_READ is requested, the device SHOULD return the +RPMB frame with the response, the calculated MAC and the result: + +\begin{enumerate} +\item If the \field{block_count} is not set to 1 then + VIRTIO_RPMB_RES_GENERAL_FAILURE SHOULD be responded as \field{result}. + +\item If the programming of authentication key fails, + then VIRTIO_RPMB_RES_WRITE_FAILURE SHOULD be responded as \field{result}. + +\item If some other error occurs then returned result + VIRTIO_RPMB_RES_GENERAL_FAILURE SHOULD be responded as \field{result}. + +\item The \field{req_resp} value VIRTIO_RPMB_RESP_PROGRAM_KEY SHOULD be responded. +\end{enumerate} + +\devicenormative{\paragraph}{Device Operation: Get Write Counter}{Device Types / RPMB Device / Device Operation / Device Operation: Get Write Counter} + +If the authentication key is not yet programmed then VIRTIO_RPMB_RES_NO_AUTH_KEY +SHOULD be returned in \field{result}. + +If block count has not been set to 1 then VIRTIO_RPMB_RES_GENERAL_FAILURE +SHOULD be responded as \field{result}. + +The \field{req_resp} value VIRTIO_RPMB_RESP_GET_COUNTER SHOULD be responded. + +\devicenormative{\paragraph}{Device Operation: Data Write}{Device Types / RPMB Device / Device Operation / Device Operation: Data Write} + +If VIRTIO_RPMB_REQ_RESULT_READ is requested, the device SHOULD return the RPMB data +frame with the response VIRTIO_RPMB_RESP_DATA_WRITE, the incremented counter value, +the data address, the calculated MAC and the result: + +\begin{enumerate} +\item If the authentication key is not yet programmed, + then VIRTIO_RPMB_RES_NO_AUTH_KEY SHOULD be returned in \field{result}. + +\item If block count is zero or greater than \field{max_wr_cnt} then + VIRTIO_RPMB_RES_GENERAL_FAILURE SHOULD be responded. + +\item The device MUST check whether the write counter has expired. + If the write counter is expired then the \field{result} SHOULD be set to + VIRTIO_RPMB_RES_WRITE_COUNTER_EXPIRED. + +\item If there is an error in the address (out of range) then the \field{result} + SHOULD be set to VIRTIO_RPMB_RES_ADDR_FAILURE. + +\item The device MUST calculate the MAC taking authentication key and frame as input, + and compare this with the MAC in the request. If the two MAC’s are different + then VIRTIO_RPMB_RES_AUTH_FAILURE SHOULD be returned in \field{result}. + +\item If the writer counter in the request is different from the one maintained + by the device then VIRTIO_RPMB_RES_COUNT_FAILURE SHOULD be returned in \field{result}. + +\item If the MAC and write counter comparisons are matched then the write request + is considered to be authenticated. The data from the request SHOULD be written to the + address indicated in the request and the write counter SHOULD be incremented by 1. + +\item If the write fails then the \field{result} SHOULD be VIRTIO_RPMB_RES_WRITE_FAILURE. + +\item If some other error occurs during the writing procedure then the \field{result} + SHOULD be VIRTIO_RPMB_RES_GENERAL_FAILURE. + +\item The \field{req_resp} value VIRTIO_RPMB_RESP_DATA_WRITE SHOULD be responded. +\end{enumerate} + +\devicenormative{\paragraph}{Device Operation: Data Read}{Device Types / RPMB Device / Device Operation / Device Operation: Data Read} + +If the authentication key is not yet programmed then VIRTIO_RPMB_RES_NO_AUTH_KEY +SHOULD be returned in \field{result}. + +If block count has not been set to 1 then VIRTIO_RPMB_RES_GENERAL_FAILURE SHOULD be +responded as \field{result}. + +If there is an error in the address (out of range) then the \field{result} SHOULD +be set to VIRTIO_RPMB_RES_ADDR_FAILURE. + +If data fetch from addressed location inside the device fails then the \field{result} +SHOULD be VIRTIO_RPMB_RES_READ_FAILURE. + +If some other error occurs during the read procedure then the \field{result} +SHOULD be VIRTIO_RPMB_RES_GENERAL_FAILURE. + +The \field{req_resp} value VIRTIO_RPMB_RESP_DATA_READ SHOULD be responded. + +\devicenormative{\paragraph}{Device Operation: Result Read}{Device Types / RPMB Device / Device Operation / Device Operation: Result Read} + +If the \field{block_count} has not been set to 1 of VIRTIO_RPMB_REQ_RESULT_READ +request then VIRTIO_RPMB_RES_GENERAL_FAILURE SHOULD be responded as \field{result}. + +\drivernormative{\subsubsection}{Device Operation}{Device Types / RPMB Device / Device Operation} + +The RPMB frames MUST not be packed by the driver. +The driver MUST configure, initialize and format virtqueue for the RPMB requests received from its caller then send it to the device. + +\devicenormative{\subsubsection}{Device Operation}{Device Types / RPMB Device / Device Operation} + +The virtio-rpmb device could be backed in a number of ways. It SHOULD + keep consistent behaviors with hardware as described in paragraph + 6.6.22 of \hyperref[intro:eMMC]{eMMC}. + Some elements are maintained by the device: +\begin{enumerate} +\item The device MUST maintain a one-time programmable authentication key. + It cannot be overwritten, erased or read. The key is used to + authenticate the accesses when MAC is calculated. This key MUST be + kept regardless of device reset or reboot. +\item The device MUST maintain a read-only monotonic write counter. It + MUST be initialized to zero and added by one automatically along with + successful write operation. The value cannot be reset. After + the counter has reached its maximum value 0xFFFF FFFF, it will + not be incremented anymore. This counter MUST be kept regardless + of device reset or reboot. +\item The device MUST maintain the data for read/write via authenticated + access. +\end{enumerate} |