xen: properly gate host writes of modified PCI CFG contents

The old logic didn't work as intended when an access spanned multiple
fields (for example a 32-bit access to the location of the MSI Message
Data field with the high 16 bits not being covered by any known field).
Remove it and derive which fields not to write to from the accessed
fields' emulation masks: When they're all ones, there's no point in
doing any host write.

This fixes a secondary issue at once: We obviously shouldn't make any
host write attempt when already the host read failed.

This is XSA-128.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>

diff --git a/hw/xen/xen_pt.c b/hw/xen/xen_pt.c
index d9d08850e3d00bf5c3fa49b64ab318ffd733ec0c..da3953e8e316125e5ff2cb72887b75b8e4ea8220 100644 (file)
--- a/hw/xen/xen_pt.c
+++ b/hw/xen/xen_pt.c
@@ -234,7 +234,7 @@ static void xen_pt_pci_write_config(PCIDevice *d, uint32_t addr,
     int index = 0;
     XenPTRegGroup *reg_grp_entry = NULL;
     int rc = 0;
-    uint32_t read_val = 0;
+    uint32_t read_val = 0, wb_mask;
     int emul_len = 0;
     XenPTReg *reg_entry = NULL;
     uint32_t find_addr = addr;
@@ -271,6 +271,9 @@ static void xen_pt_pci_write_config(PCIDevice *d, uint32_t addr,
     if (rc < 0) {
         XEN_PT_ERR(d, "pci_read_block failed. return value: %d.\n", rc);
         memset(&read_val, 0xff, len);
+        wb_mask = 0;
+    } else {
+        wb_mask = 0xFFFFFFFF >> ((4 - len) << 3);
     }
 
     /* pass directly to the real device for passthrough type register group */
@@ -298,6 +301,11 @@ static void xen_pt_pci_write_config(PCIDevice *d, uint32_t addr,
 
             valid_mask <<= (find_addr - real_offset) << 3;
             ptr_val = (uint8_t *)&val + (real_offset & 3);
+            if (reg->emu_mask == (0xFFFFFFFF >> ((4 - reg->size) << 3))) {
+                wb_mask &= ~((reg->emu_mask
+                              >> ((find_addr - real_offset) << 3))
+                             << ((len - emul_len) << 3));
+            }
 
             /* do emulation based on register size */
             switch (reg->size) {
@@ -350,10 +358,19 @@ static void xen_pt_pci_write_config(PCIDevice *d, uint32_t addr,
     memory_region_transaction_commit();
 
 out:
-    if (!(reg && reg->no_wb)) {
+    for (index = 0; wb_mask; index += len) {
         /* unknown regs are passed through */
-        rc = xen_host_pci_set_block(&s->real_device, addr,
-                                    (uint8_t *)&val, len);
+        while (!(wb_mask & 0xff)) {
+            index++;
+            wb_mask >>= 8;
+        }
+        len = 0;
+        do {
+            len++;
+            wb_mask >>= 8;
+        } while (wb_mask & 0xff);
+        rc = xen_host_pci_set_block(&s->real_device, addr + index,
+                                    (uint8_t *)&val + index, len);
 
         if (rc < 0) {
             XEN_PT_ERR(d, "pci_write_block failed. return value: %d.\n", rc);

diff --git a/hw/xen/xen_pt.h b/hw/xen/xen_pt.h
index 942dc60cc72f82e37eea03b46f50e6f15c08318a..52ceb856f9794b2471321ce544aa5dc72a721141 100644 (file)
--- a/hw/xen/xen_pt.h
+++ b/hw/xen/xen_pt.h
@@ -105,8 +105,6 @@ struct XenPTRegInfo {
     uint32_t ro_mask;
     /* reg emulate field mask (ON:emu, OFF:passthrough) */
     uint32_t emu_mask;
-    /* no write back allowed */
-    uint32_t no_wb;
     xen_pt_conf_reg_init init;
     /* read/write function pointer
      * for double_word/word/byte size */

diff --git a/hw/xen/xen_pt_config_init.c b/hw/xen/xen_pt_config_init.c
index c4c031935dab49cda96c1824b26de003b8f716ef..fd732819ca2fcd8792a88f5ed41030e5055274bd 100644 (file)
--- a/hw/xen/xen_pt_config_init.c
+++ b/hw/xen/xen_pt_config_init.c
@@ -1281,7 +1281,6 @@ static XenPTRegInfo xen_pt_emu_reg_msi[] = {
         .init_val   = 0x00000000,
         .ro_mask    = 0x00000003,
         .emu_mask   = 0xFFFFFFFF,
-        .no_wb      = 1,
         .init       = xen_pt_common_reg_init,
         .u.dw.read  = xen_pt_long_reg_read,
         .u.dw.write = xen_pt_msgaddr32_reg_write,
@@ -1293,7 +1292,6 @@ static XenPTRegInfo xen_pt_emu_reg_msi[] = {
         .init_val   = 0x00000000,
         .ro_mask    = 0x00000000,
         .emu_mask   = 0xFFFFFFFF,
-        .no_wb      = 1,
         .init       = xen_pt_msgaddr64_reg_init,
         .u.dw.read  = xen_pt_long_reg_read,
         .u.dw.write = xen_pt_msgaddr64_reg_write,
@@ -1305,7 +1303,6 @@ static XenPTRegInfo xen_pt_emu_reg_msi[] = {
         .init_val   = 0x0000,
         .ro_mask    = 0x0000,
         .emu_mask   = 0xFFFF,
-        .no_wb      = 1,
         .init       = xen_pt_msgdata_reg_init,
         .u.w.read   = xen_pt_word_reg_read,
         .u.w.write  = xen_pt_msgdata_reg_write,
@@ -1317,7 +1314,6 @@ static XenPTRegInfo xen_pt_emu_reg_msi[] = {
         .init_val   = 0x0000,
         .ro_mask    = 0x0000,
         .emu_mask   = 0xFFFF,
-        .no_wb      = 1,
         .init       = xen_pt_msgdata_reg_init,
         .u.w.read   = xen_pt_word_reg_read,
         .u.w.write  = xen_pt_msgdata_reg_write,