Re: [Stratos-dev] [RFC PATCH 15/19] tools/vhost-user-rpmb: implement VIRTIO_RPMB_REQ_DATA_WRITE

Joakim Bech joakim.bech@linaro.org 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@linaro.org

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!