diff --git a/block.c b/block.c
index 809ec54587..35f7a0a0ab 100644
--- a/block.c
+++ b/block.c
@@ -662,8 +662,8 @@ BlockDriver *bdrv_find_protocol(const char *filename,
  * probing score.
  * Return the first block driver with the highest probing score.
  */
-static BlockDriver *bdrv_probe_all(const uint8_t *buf, int buf_size,
-                                   const char *filename)
+BlockDriver *bdrv_probe_all(const uint8_t *buf, int buf_size,
+                            const char *filename)
 {
     int score_max = 0, score;
     BlockDriver *drv = NULL, *d;
@@ -1489,6 +1489,7 @@ int bdrv_open(BlockDriverState **pbs, const char *filename,
     }
 
     /* Image format probing */
+    bs->probed = !drv;
     if (!drv && file) {
         ret = find_image_format(file, filename, &drv, &local_err);
         if (ret < 0) {
diff --git a/block/raw_bsd.c b/block/raw_bsd.c
index 401b967e85..2ce5409044 100644
--- a/block/raw_bsd.c
+++ b/block/raw_bsd.c
@@ -58,8 +58,58 @@ static int coroutine_fn raw_co_readv(BlockDriverState *bs, int64_t sector_num,
 static int coroutine_fn raw_co_writev(BlockDriverState *bs, int64_t sector_num,
                                       int nb_sectors, QEMUIOVector *qiov)
 {
+    void *buf = NULL;
+    BlockDriver *drv;
+    QEMUIOVector local_qiov;
+    int ret;
+
+    if (bs->probed && sector_num == 0) {
+        /* As long as these conditions are true, we can't get partial writes to
+         * the probe buffer and can just directly check the request. */
+        QEMU_BUILD_BUG_ON(BLOCK_PROBE_BUF_SIZE != 512);
+        QEMU_BUILD_BUG_ON(BDRV_SECTOR_SIZE != 512);
+
+        if (nb_sectors == 0) {
+            /* qemu_iovec_to_buf() would fail, but we want to return success
+             * instead of -EINVAL in this case. */
+            return 0;
+        }
+
+        buf = qemu_try_blockalign(bs->file, 512);
+        if (!buf) {
+            ret = -ENOMEM;
+            goto fail;
+        }
+
+        ret = qemu_iovec_to_buf(qiov, 0, buf, 512);
+        if (ret != 512) {
+            ret = -EINVAL;
+            goto fail;
+        }
+
+        drv = bdrv_probe_all(buf, 512, NULL);
+        if (drv != bs->drv) {
+            ret = -EPERM;
+            goto fail;
+        }
+
+        /* Use the checked buffer, a malicious guest might be overwriting its
+         * original buffer in the background. */
+        qemu_iovec_init(&local_qiov, qiov->niov + 1);
+        qemu_iovec_add(&local_qiov, buf, 512);
+        qemu_iovec_concat(&local_qiov, qiov, 512, qiov->size - 512);
+        qiov = &local_qiov;
+    }
+
     BLKDBG_EVENT(bs->file, BLKDBG_WRITE_AIO);
-    return bdrv_co_writev(bs->file, sector_num, nb_sectors, qiov);
+    ret = bdrv_co_writev(bs->file, sector_num, nb_sectors, qiov);
+
+fail:
+    if (qiov == &local_qiov) {
+        qemu_iovec_destroy(&local_qiov);
+    }
+    qemu_vfree(buf);
+    return ret;
 }
 
 static int64_t coroutine_fn raw_co_get_block_status(BlockDriverState *bs,
@@ -158,6 +208,18 @@ static int raw_open(BlockDriverState *bs, QDict *options, int flags,
                     Error **errp)
 {
     bs->sg = bs->file->sg;
+
+    if (bs->probed && !bdrv_is_read_only(bs)) {
+        fprintf(stderr,
+                "WARNING: Image format was not specified for '%s' and probing "
+                "guessed raw.\n"
+                "         Automatically detecting the format is dangerous for "
+                "raw images, write operations on block 0 will be restricted.\n"
+                "         Specify the 'raw' format explicitly to remove the "
+                "restrictions.\n",
+                bs->file->filename);
+    }
+
     return 0;
 }
 
diff --git a/include/block/block_int.h b/include/block/block_int.h
index cd94559a64..192fce8760 100644
--- a/include/block/block_int.h
+++ b/include/block/block_int.h
@@ -326,6 +326,7 @@ struct BlockDriverState {
     int sg;        /* if true, the device is a /dev/sg* */
     int copy_on_read; /* if true, copy read backing sectors into image
                          note this is a reference count */
+    bool probed;
 
     BlockDriver *drv; /* NULL means no media */
     void *opaque;
@@ -414,6 +415,8 @@ struct BlockDriverState {
 };
 
 int get_tmp_filename(char *filename, int size);
+BlockDriver *bdrv_probe_all(const uint8_t *buf, int buf_size,
+                            const char *filename);
 
 void bdrv_set_io_limits(BlockDriverState *bs,
                         ThrottleConfig *cfg);