drivers/char: mark DMA buffers as reserved for the XHCI

The important part is to include those buffers in IOMMU page table
relevant for the USB controller. Otherwise, DbC will stop working as
soon as IOMMU is enabled, regardless of to which domain device assigned
(be it xen or dom0).
If the device is passed through to dom0 or other domain (see later
patches), that domain will effectively have access to those buffers too.
It does give such domain yet another way to DoS the system (as is the
case when having PCI device assigned already), but also possibly steal
the console ring content. Thus, such domain should be a trusted one.
In any case, prevent anything else being placed on those pages by adding
artificial padding.

Signed-off-by: Marek Marczykowski-Górecki <marmarek@invisiblethingslab.com>
Acked-by: Jan Beulich <jbeulich@suse.com>

diff --git a/xen/drivers/char/xhci-dbc.c b/xen/drivers/char/xhci-dbc.c
index 4712faaabef73b3bd59ae0fc19b962816e0d0b3d..f55f73e382fc38180d7d36fd0d6ba8333c283d4b 100644 (file)
--- a/xen/drivers/char/xhci-dbc.c
+++ b/xen/drivers/char/xhci-dbc.c
@@ -20,6 +20,7 @@
  */
 
 #include <xen/delay.h>
+#include <xen/iommu.h>
 #include <xen/mm.h>
 #include <xen/param.h>
 #include <xen/serial.h>
@@ -1051,13 +1052,21 @@ static struct uart_driver dbc_uart_driver = {
 };
 
 /* Those are accessed via DMA. */
-static struct xhci_trb evt_trb[DBC_TRB_RING_CAP];
-static struct xhci_trb out_trb[DBC_TRB_RING_CAP];
-static struct xhci_trb in_trb[DBC_TRB_RING_CAP];
-static struct xhci_erst_segment erst __aligned(16);
-static struct xhci_dbc_ctx ctx __aligned(16);
-static uint8_t out_wrk_buf[DBC_WORK_RING_CAP];
-static struct xhci_string_descriptor str_buf[DBC_STRINGS_COUNT];
+struct dbc_dma_bufs {
+    struct xhci_trb evt_trb[DBC_TRB_RING_CAP];
+    struct xhci_trb out_trb[DBC_TRB_RING_CAP];
+    struct xhci_trb in_trb[DBC_TRB_RING_CAP];
+    uint8_t out_wrk_buf[DBC_WORK_RING_CAP];
+    struct xhci_erst_segment erst __aligned(16);
+    struct xhci_dbc_ctx ctx __aligned(16);
+    struct xhci_string_descriptor str_buf[DBC_STRINGS_COUNT];
+    /*
+     * Don't place anything else on this page - it will be
+     * DMA-reachable by the USB controller.
+     */
+};
+static struct dbc_dma_bufs __section(".bss.page_aligned") __aligned(PAGE_SIZE)
+    dbc_dma_bufs;
 
 static int __init xhci_parse_dbgp(const char *opt_dbgp)
 {
@@ -1104,16 +1113,22 @@ void __init xhci_dbc_uart_init(void)
     if ( !dbc->enable )
         return;
 
-    dbc->dbc_ctx = &ctx;
-    dbc->dbc_erst = &erst;
-    dbc->dbc_ering.trb = evt_trb;
-    dbc->dbc_oring.trb = out_trb;
-    dbc->dbc_iring.trb = in_trb;
-    dbc->dbc_owork.buf = out_wrk_buf;
-    dbc->dbc_str = str_buf;
+    dbc->dbc_ctx = &dbc_dma_bufs.ctx;
+    dbc->dbc_erst = &dbc_dma_bufs.erst;
+    dbc->dbc_ering.trb = dbc_dma_bufs.evt_trb;
+    dbc->dbc_oring.trb = dbc_dma_bufs.out_trb;
+    dbc->dbc_iring.trb = dbc_dma_bufs.in_trb;
+    dbc->dbc_owork.buf = dbc_dma_bufs.out_wrk_buf;
+    dbc->dbc_str = dbc_dma_bufs.str_buf;
 
     if ( dbc_open(dbc) )
+    {
+        iommu_add_extra_reserved_device_memory(
+                PFN_DOWN(virt_to_maddr(&dbc_dma_bufs)),
+                PFN_UP(sizeof(dbc_dma_bufs)),
+                uart->dbc.sbdf);
         serial_register_uart(SERHND_XHCI, &dbc_uart_driver, &dbc_uart);
+    }
 }
 
 #ifdef DBC_DEBUG