hw/dmax/xlnx_dpdma: fix handling of address_extension descriptor fields

The DMA descriptor structures for this device have
a set of "address extension" fields which extend the 32
bit source addresses with an extra 16 bits to give a
48 bit address:
 https://docs.amd.com/r/en-US/ug1085-zynq-ultrascale-trm/ADDR_EXT-Field

However, we misimplemented this address extension in several ways:
 * we only extracted 12 bits of the extension fields, not 16
 * we didn't shift the extension field up far enough
 * we accidentally did the shift as 32-bit arithmetic, which
   meant that we would have an overflow instead of setting
   bits [47:32] of the resulting 64-bit address

Add a type cast and use extract64() instead of extract32()
to avoid integer overflow on addition. Fix bit fields
extraction according to documentation.

Found by Linux Verification Center (linuxtesting.org) with SVACE.

Cc: qemu-stable@nongnu.org
Fixes: d3c6369a96 ("introduce xlnx-dpdma")
Signed-off-by: Alexandra Diupina <adiupina@astralinux.ru>
Message-id: 20240428181131.23801-1-adiupina@astralinux.ru
[PMM: adjusted commit message]
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

hw/dma/xlnx_dpdma.c

@@ -175,24 +175,24 @@ static uint64_t xlnx_dpdma_desc_get_source_address(DPDMADescriptor *desc,
 
     switch (frag) {
     case 0:
-        addr = desc->source_address
-            + (extract32(desc->address_extension, 16, 12) << 20);
+        addr = (uint64_t)desc->source_address
+            + (extract64(desc->address_extension, 16, 16) << 32);
         break;
     case 1:
-        addr = desc->source_address2
-            + (extract32(desc->address_extension_23, 0, 12) << 8);
+        addr = (uint64_t)desc->source_address2
+            + (extract64(desc->address_extension_23, 0, 16) << 32);
         break;
     case 2:
-        addr = desc->source_address3
-            + (extract32(desc->address_extension_23, 16, 12) << 20);
+        addr = (uint64_t)desc->source_address3
+            + (extract64(desc->address_extension_23, 16, 16) << 32);
         break;
     case 3:
-        addr = desc->source_address4
-            + (extract32(desc->address_extension_45, 0, 12) << 8);
+        addr = (uint64_t)desc->source_address4
+            + (extract64(desc->address_extension_45, 0, 16) << 32);
         break;
     case 4:
-        addr = desc->source_address5
-            + (extract32(desc->address_extension_45, 16, 12) << 20);
+        addr = (uint64_t)desc->source_address5
+            + (extract64(desc->address_extension_45, 16, 16) << 32);
         break;
     default:
         addr = 0;