Joakim Bech <joakim.bech@xxxxxxxxxx> writes:
> On Fri, Sep 25, 2020 at 01:51:43PM +0100, Alex Bennée wrote:
>> With this command we are finally updating data to the backing store
>> and cycling the write_count and each successful write. We also include
>> the write count in all response frames as the spec is a little unclear
>> but the example test code expected it.
>>
>> Signed-off-by: Alex Bennée <alex.bennee@xxxxxxxxxx>
>> ---
>> tools/vhost-user-rpmb/main.c | 111 +++++++++++++++++++++++++++++++++--
>> 1 file changed, 105 insertions(+), 6 deletions(-)
>>
>> diff --git a/tools/vhost-user-rpmb/main.c b/tools/vhost-user-rpmb/main.c
>> index 88747c50fa44..a17c3b4bcc4e 100644
>> --- a/tools/vhost-user-rpmb/main.c
>> +++ b/tools/vhost-user-rpmb/main.c
>> @@ -62,6 +62,7 @@ enum {
>> #define KiB (1UL << 10)
>> #define MAX_RPMB_SIZE (KiB * 128 * 256)
>> #define RPMB_KEY_MAC_SIZE 32
>> +#define RPMB_BLOCK_SIZE 256
>>
>> /* RPMB Request Types */
>> #define VIRTIO_RPMB_REQ_PROGRAM_KEY 0x0001
>> @@ -100,7 +101,7 @@ struct virtio_rpmb_config {
>> struct virtio_rpmb_frame {
>> uint8_t stuff[196];
>> uint8_t key_mac[RPMB_KEY_MAC_SIZE];
>> - uint8_t data[256];
>> + uint8_t data[RPMB_BLOCK_SIZE];
>> uint8_t nonce[16];
>> /* remaining fields are big-endian */
>> uint32_t write_counter;
>> @@ -124,6 +125,7 @@ typedef struct VuRpmb {
>> uint8_t last_nonce[16];
>> uint16_t last_result;
>> uint16_t last_reqresp;
>> + uint16_t last_address;
>> uint32_t write_count;
>> } VuRpmb;
>>
>> @@ -239,17 +241,30 @@ vrpmb_set_config(VuDev *dev, const uint8_t *data,
>> * which itself uses a 3 clause BSD chunk of code.
>> */
>>
>> +static const int rpmb_frame_dlen = (sizeof(struct virtio_rpmb_frame) -
>> + offsetof(struct virtio_rpmb_frame, data));
>> +
>> static void vrpmb_update_mac_in_frame(VuRpmb *r, struct virtio_rpmb_frame *frm)
>> {
>> hmac_sha256_ctx ctx;
>> - static const int dlen = (sizeof(struct virtio_rpmb_frame) -
>> - offsetof(struct virtio_rpmb_frame, data));
>>
>> hmac_sha256_init(&ctx, r->key, RPMB_KEY_MAC_SIZE);
>> - hmac_sha256_update(&ctx, frm->data, dlen);
>> + hmac_sha256_update(&ctx, frm->data, rpmb_frame_dlen);
>> hmac_sha256_final(&ctx, &frm->key_mac[0], 32);
>> }
>>
>> +static bool vrpmb_verify_mac_in_frame(VuRpmb *r, struct virtio_rpmb_frame *frm)
>> +{
>> + hmac_sha256_ctx ctx;
>> + uint8_t calculated_mac[RPMB_KEY_MAC_SIZE];
>> +
>> + hmac_sha256_init(&ctx, r->key, RPMB_KEY_MAC_SIZE);
>> + hmac_sha256_update(&ctx, frm->data, rpmb_frame_dlen);
>> + hmac_sha256_final(&ctx, calculated_mac, RPMB_KEY_MAC_SIZE);
>> +
>> + return memcmp(calculated_mac, frm->key_mac, RPMB_KEY_MAC_SIZE) == 0;
>>
> I'd prefer using a constant time comparison function for this one
> instead of memcmp (regardless if it's used for simulation or not) to
> prevent eventual timing attacks.
Could you recommend such a function for this?
>
>> +}
>> +
>> /*
>> * Handlers for individual control messages
>> */
>> @@ -324,6 +339,82 @@ vrpmb_handle_get_write_counter(VuDev *dev, struct virtio_rpmb_frame *frame)
>> return resp;
>> }
>>
>> +/*
>> + * vrpmb_handle_write:
>> + *
>> + * We will report the success/fail on receipt of
>> + * VIRTIO_RPMB_REQ_RESULT_READ. Returns the number of extra frames
>> + * processed in the request.
>> + */
>> +static int vrpmb_handle_write(VuDev *dev, struct virtio_rpmb_frame *frame)
>> +{
>> + VuRpmb *r = container_of(dev, VuRpmb, dev.parent);
>> + int extra_frames = 0;
>> + uint16_t block_count = be16toh(frame->block_count);
>> + uint32_t write_counter = be32toh(frame->write_counter);
>> + size_t offset;
>> +
>> + r->last_reqresp = VIRTIO_RPMB_RESP_DATA_WRITE;
>> + r->last_address = be16toh(frame->address);
>> + offset = r->last_address * RPMB_BLOCK_SIZE;
>> +
>> + /*
>> + * Run the checks from:
>> + * 5.12.6.1.3 Device Requirements: Device Operation: Data Write
>> + */
>> + if (!r->key) {
>> + g_warning("no key programmed");
>> + r->last_result = VIRTIO_RPMB_RES_NO_AUTH_KEY;
>> + } else if (block_count == 0 ||
>> + block_count > r->virtio_config.max_wr_cnt) {
>> + r->last_result = VIRTIO_RPMB_RES_GENERAL_FAILURE;
>> + } else if (false /* what does an expired write counter mean? */) {
>>
> IIRC, the counter has room for a 32-bit value and the counter will never
> wrap around. So once the counter have reached max for uint32_t, then
> there is an additional bit set (permanently) in the operation result.
> I.e., writes are no longer possible once that has happened. That is
> probably what you're referring to here I suppose.
That would make sense. I'll see if I can make the spec language a bit
clearer as well.
>
>> + r->last_result = VIRTIO_RPMB_RES_WRITE_COUNTER_EXPIRED;
>> + } else if (offset > (r->virtio_config.capacity * (128 * KiB))) {
>> + r->last_result = VIRTIO_RPMB_RES_ADDR_FAILURE;
>> + } else if (!vrpmb_verify_mac_in_frame(r, frame)) {
>> + r->last_result = VIRTIO_RPMB_RES_AUTH_FAILURE;
>> + } else if (write_counter != r->write_count) {
>> + r->last_result = VIRTIO_RPMB_RES_COUNT_FAILURE;
>> + } else {
>> + int i;
>> + /* At this point we have a valid authenticated write request
>> + * so the counter can incremented and we can attempt to
>> + * update the backing device.
>> + */
>> + r->write_count++;
>> + for (i = 0; i < block_count; i++) {
>> + void *blk = r->flash_map + offset;
>> + g_debug("%s: writing block %d", __func__, i);
>> + if (mprotect(blk, RPMB_BLOCK_SIZE, PROT_WRITE) != 0) {
>> + r->last_result = VIRTIO_RPMB_RES_WRITE_FAILURE;
>> + break;
>> + }
>> + memcpy(blk, frame[i].data, RPMB_BLOCK_SIZE);
>> + if (msync(blk, RPMB_BLOCK_SIZE, MS_SYNC) != 0) {
>> + g_warning("%s: failed to sync update", __func__);
>> + r->last_result = VIRTIO_RPMB_RES_WRITE_FAILURE;
>> + break;
>> + }
>> + if (mprotect(blk, RPMB_BLOCK_SIZE, PROT_READ) != 0) {
>> + g_warning("%s: failed to re-apply read protection", __func__);
>> + r->last_result = VIRTIO_RPMB_RES_GENERAL_FAILURE;
>> + break;
>> + }
>> + offset += RPMB_BLOCK_SIZE;
>> + }
>> + r->last_result = VIRTIO_RPMB_RES_OK;
>> + extra_frames = i - 1;
>> + }
>> +
>> + g_info("%s: %s (%x, %d extra frames processed), write_count=%d", __func__,
>> + r->last_result == VIRTIO_RPMB_RES_OK ? "successful":"failed",
>> + r->last_result, extra_frames, r->write_count);
>> +
>> + return extra_frames;
>> +}
>> +
>> +
>> /*
>> * Return the result of the last message. This is only valid if the
>> * previous message was VIRTIO_RPMB_REQ_PROGRAM_KEY or
>> @@ -339,10 +430,14 @@ static struct virtio_rpmb_frame * vrpmb_handle_result_read(VuDev *dev)
>> g_info("%s: for request:%x result:%x", __func__,
>> r->last_reqresp, r->last_result);
>>
>> - if (r->last_reqresp == VIRTIO_RPMB_RESP_PROGRAM_KEY ||
>> - r->last_reqresp == VIRTIO_RPMB_REQ_DATA_WRITE) {
>> + if (r->last_reqresp == VIRTIO_RPMB_RESP_PROGRAM_KEY) {
>> resp->result = htobe16(r->last_result);
>> resp->req_resp = htobe16(r->last_reqresp);
>> + } else if (r->last_reqresp == VIRTIO_RPMB_RESP_DATA_WRITE) {
>> + resp->result = htobe16(r->last_result);
>> + resp->req_resp = htobe16(r->last_reqresp);
>> + resp->write_counter = htobe32(r->write_count);
>> + resp->address = htobe16(r->last_address);
>> } else {
>> resp->result = htobe16(VIRTIO_RPMB_RES_GENERAL_FAILURE);
>> }
>> @@ -445,6 +540,10 @@ vrpmb_handle_ctrl(VuDev *dev, int qidx)
>> __func__);
>> }
>> break;
>> + case VIRTIO_RPMB_REQ_DATA_WRITE:
>> + /* we can have multiple blocks handled */
>> + n += vrpmb_handle_write(dev, f);
>> + break;
>> default:
>> g_debug("un-handled request: %x", f->req_resp);
>> break;
>> --
>> 2.20.1
>>
Thanks!
--
Alex Bennée
_______________________________________________
Virtualization mailing list
Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx
https://lists.linuxfoundation.org/mailman/listinfo/virtualization
