[PATCH 1/1] hw/cxl: fix OOB access in cxl_doe_cdat_rsp via entry_handle

From: Haotian Jiang <[email protected]>

cxl_doe_cdat_rsp() takes ent = req->entry_handle (uint16_t, fully
guest-controlled, 0..0xFFFF) and directly indexes cdat->entry[ent]
without checking ent < cdat->entry_len. For a default cxl-type3 with
one volatile memory region, entry_len = 1 + CT3_CDAT_NUM_ENTRIES = 7,
so any entry_handle >= 7 reads past the CDATEntry array into host heap.

The OOB-read base/length are then used in
memcpy(read_mbox + offset, base, len) at cxl_type3.c:298-299, leaking
host heap memory to the guest via PCI_EXP_DOE_RD_DATA_MBOX, and
potentially overflowing the 1 MiB read_mbox heap buffer when the OOB
length field is large.

The same bug exists in the cxl-upstream implementation.

Existing checks do not bound ent: assert(cdat->entry_len) only ensures
the table is loaded; the minimum-length check only guards against a
truncated CDATReq; the entry_handle ternary at line 293 only decides
the next-handle echo, not the current access; pcie_doe_get_obj_len
reads header.length, not entry_handle.

Reproduce: build QEMU with CONFIG_CXL, boot
  -M q35,cxl=on -device pxb-cxl,bus_nr=52 ... -device cxl-type3,...
then send a CDATReq with entry_handle=0xFFFF via the DOE mailbox at
config offset 0x190. Under ASAN this reports SEGV in cxl_doe_cdat_rsp
at cxl_type3.c:281.

Fixes: f5ee7413d5 ("hw/mem/cxl-type3: Add CXL CDAT Data Object Exchange")
Fixes: 882877fc35 ("hw/pci-bridge/cxl-upstream: Add a CDAT table access DOE")
Signed-off-by: Haotian Jiang <[email protected]>
Cc: [email protected]
---
 hw/mem/cxl_type3.c           | 3 +++
 hw/pci-bridge/cxl_upstream.c | 3 +++
 2 files changed, 6 insertions(+)

diff --git a/hw/mem/cxl_type3.c b/hw/mem/cxl_type3.c
index cba05ec57d..28f41fa623 100644
--- a/hw/mem/cxl_type3.c
+++ b/hw/mem/cxl_type3.c
@@ -278,6 +278,9 @@ static bool cxl_doe_cdat_rsp(DOECap *doe_cap)
     }
 
     ent = req->entry_handle;
+    if (ent >= cdat->entry_len) {
+        return false;
+    }
     base = cdat->entry[ent].base;
     len = cdat->entry[ent].length;
 
diff --git a/hw/pci-bridge/cxl_upstream.c b/hw/pci-bridge/cxl_upstream.c
index b6281cbd4c..69773ff163 100644
--- a/hw/pci-bridge/cxl_upstream.c
+++ b/hw/pci-bridge/cxl_upstream.c
@@ -158,6 +158,9 @@ static bool cxl_doe_cdat_rsp(DOECap *doe_cap)
     }
 
     ent = req->entry_handle;
+    if (ent >= cdat->entry_len) {
+        return false;
+    }
     base = cdat->entry[ent].base;
     len = cdat->entry[ent].length;
 
-- 
2.34.1