[xen master] drivers/char: mark DMA buffers as reserved for the XHCI

[patchbot@xxxxxxx]

commit 3a1a7b809ffa4251a9673858a75b161c49c6c241
Author:     Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>
AuthorDate: Mon Sep 26 11:11:33 2022 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Mon Sep 26 11:11:33 2022 +0200

    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@xxxxxxxxxxxxxxxxxxxxxx>
    Acked-by: Jan Beulich <jbeulich@xxxxxxxx>
---
 xen/drivers/char/xhci-dbc.c | 43 +++++++++++++++++++++++++++++--------------
 1 file changed, 29 insertions(+), 14 deletions(-)

diff --git a/xen/drivers/char/xhci-dbc.c b/xen/drivers/char/xhci-dbc.c
index 4712faaabe..f55f73e382 100644
--- 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
--
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