[PATCH for-4.21] vpci/msix: improve handling of bogus MSI-X capabilities

[Roger Pau Monne <roger.pau@xxxxxxxxxx>]

I've had the luck to come across a PCI card that exposes a MSI-X capability
where the BIR of the vector and PBA tables points at a BAR that has 0 size.

This doesn't play nice with the code in vpci_make_msix_hole(), as it would
still use the address of such empty BAR (0) and attempt to crave a hole in
the p2m.  This leads to errors like the one below being reported by Xen:

d0v0 0000:22:00.0: existing mapping (mfn: 181c4300 type: 0) at 0 clobbers MSIX 
MMIO area

And the device left unable to enable memory decoding due to the failure
reported by vpci_make_msix_hole().

Introduce checking in init_msix() to ensure the BARs containing the MSI-X
tables are usable.  This requires checking that the BIR points to a
non-empty BAR, and the offset and size of the MSI-X tables can fit in the
target BAR.

This fixes booting PVH dom0 on Supermicro AS -2126HS-TN severs with AMD
EPYC 9965 processors.  The broken device is:

22:00.0 SATA controller: Advanced Micro Devices, Inc. [AMD] FCH SATA Controller 
[AHCI mode] (rev 93)

There are multiple of those integrated controllers in the system, all
broken in the same way.

Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
---
Cc: Stewart Hildebrand <stewart.hildebrand@xxxxxxx>
Cc: Jan Beulich <jbeulich@xxxxxxxx>
Cc: Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>

While not strictly a bugfix, I consider this a worthy improvement so that
PVH dom0 has a chance to boot on hardware that exposes such broken MSI-X
capabilities.  Hence I think this change should be considered for inclusion
into 4.21.  There a risk of regressing on hardware that was already working
with PVH, but given enough testing that should be minimal.
---
 xen/drivers/vpci/msix.c | 50 ++++++++++++++++++++++++++++++++++++-----
 1 file changed, 45 insertions(+), 5 deletions(-)

diff --git a/xen/drivers/vpci/msix.c b/xen/drivers/vpci/msix.c
index 54a5070733aa..8458955d5bbb 100644
--- a/xen/drivers/vpci/msix.c
+++ b/xen/drivers/vpci/msix.c
@@ -675,6 +675,51 @@ static int cf_check init_msix(struct pci_dev *pdev)
     if ( !msix )
         return -ENOMEM;
 
+    msix->tables[VPCI_MSIX_TABLE] =
+        pci_conf_read32(pdev->sbdf, msix_table_offset_reg(msix_offset));
+    msix->tables[VPCI_MSIX_PBA] =
+        pci_conf_read32(pdev->sbdf, msix_pba_offset_reg(msix_offset));
+
+    /* Check that the provided BAR is valid. */
+    for ( i = 0; i < ARRAY_SIZE(msix->tables); i++ )
+    {
+        const char *name = (i == VPCI_MSIX_TABLE) ? "vector" : "PBA";
+        const struct vpci_bar *bars = pdev->vpci->header.bars;
+        unsigned int bir = msix->tables[i] & PCI_MSIX_BIRMASK;
+        unsigned int type;
+        unsigned int offset = msix->tables[i] & ~PCI_MSIX_BIRMASK;
+        unsigned int size =
+            (i == VPCI_MSIX_TABLE) ? max_entries * PCI_MSIX_ENTRY_SIZE
+                                   : ROUNDUP(DIV_ROUND_UP(max_entries, 8), 8);
+
+        if ( bir >= ARRAY_SIZE(pdev->vpci->header.bars) )
+        {
+            printk(XENLOG_ERR "%pp: MSI-X %s table with out of range BIR %u\n",
+                   &pdev->sbdf, name, bir);
+ invalid:
+            xfree(msix);
+            return -ENODEV;
+
+        }
+
+        type = bars[bir].type;
+        if ( type != VPCI_BAR_MEM32 && type != VPCI_BAR_MEM64_LO )
+        {
+            printk(XENLOG_ERR
+                   "%pp: MSI-X %s table at invalid BAR%u with type %u\n",
+                   &pdev->sbdf, name, bir, type);
+            goto invalid;
+        }
+
+        if ( (uint64_t)offset + size > bars[bir].size )
+        {
+            printk(XENLOG_ERR
+                   "%pp: MSI-X %s table offset %#x size %#x outside of BAR%u 
size %#lx\n",
+                   &pdev->sbdf, name, offset, size, bir, bars[bir].size);
+            goto invalid;
+        }
+    }
+
     rc = vpci_add_register(pdev->vpci, control_read, control_write,
                            msix_control_reg(msix_offset), 2, msix);
     if ( rc )
@@ -686,11 +731,6 @@ static int cf_check init_msix(struct pci_dev *pdev)
     msix->max_entries = max_entries;
     msix->pdev = pdev;
 
-    msix->tables[VPCI_MSIX_TABLE] =
-        pci_conf_read32(pdev->sbdf, msix_table_offset_reg(msix_offset));
-    msix->tables[VPCI_MSIX_PBA] =
-        pci_conf_read32(pdev->sbdf, msix_pba_offset_reg(msix_offset));
-
     for ( i = 0; i < max_entries; i++)
     {
         msix->entries[i].masked = true;
-- 
2.51.0