[RFC PATCH 1/5] Add RegistryOpenParametersKey

[Owen Smith <owen.smith@xxxxxxxxx>]

Use IoOpenDriverRegistryKey to avoid opening an absolute registry path.
Driver Verifier can detect registry isolation violations when running WHQL
tests on Server 2025. The rule states that a driver may not open an absolute
registry key path. Use the specific API to open the 'Parameters' key with
KEY_READ when querying settings.

Signed-off-by: Owen Smith <owen.smith@xxxxxxxxx>
---
 src/common/registry.c | 22 +++++++++++++++++++++-
 src/common/registry.h |  9 ++++++++-
 src/xen/driver.c      |  2 +-
 src/xenbus/driver.c   | 19 ++-----------------
 src/xenfilt/driver.c  | 33 +++------------------------------
 5 files changed, 35 insertions(+), 50 deletions(-)

diff --git a/src/common/registry.c b/src/common/registry.c
index 0d29ddc..73a55d2 100644
--- a/src/common/registry.c
+++ b/src/common/registry.c
@@ -38,6 +38,7 @@
 
 #define REGISTRY_TAG 'GERX'
 
+static PDRIVER_OBJECT   DriverObject;
 static UNICODE_STRING   RegistryPath;
 
 static FORCEINLINE PVOID
@@ -58,7 +59,8 @@ __RegistryFree(
 
 NTSTATUS
 RegistryInitialize(
-    IN PUNICODE_STRING  Path
+    IN  PDRIVER_OBJECT  DrvObj,
+    IN  PUNICODE_STRING Path
     )
 {
     NTSTATUS            status;
@@ -69,6 +71,9 @@ RegistryInitialize(
     if (!NT_SUCCESS(status))
         goto fail1;
 
+    ASSERT3P(DriverObject, ==, NULL);
+    DriverObject = DrvObj;
+
     return STATUS_SUCCESS;
 
 fail1:
@@ -82,11 +87,26 @@ RegistryTeardown(
     VOID
     )
 {
+    DriverObject = NULL;
+
     RtlFreeUnicodeString(&RegistryPath);
     RegistryPath.Buffer = NULL;
     RegistryPath.MaximumLength = RegistryPath.Length = 0;
 }
 
+NTSTATUS
+RegistryOpenParametersKey(
+    IN  ACCESS_MASK     DesiredAccess,
+    OUT PHANDLE         Key
+    )
+{
+    return IoOpenDriverRegistryKey(DriverObject,
+                                   DriverRegKeyParameters,
+                                   DesiredAccess,
+                                   0,
+                                   Key);
+}
+
 NTSTATUS
 RegistryOpenKey(
     IN  HANDLE          Parent,
diff --git a/src/common/registry.h b/src/common/registry.h
index cbe9015..efa96ea 100644
--- a/src/common/registry.h
+++ b/src/common/registry.h
@@ -37,7 +37,8 @@
 
 extern NTSTATUS
 RegistryInitialize(
-    IN PUNICODE_STRING  Path
+    IN  PDRIVER_OBJECT  DrvObj,
+    IN  PUNICODE_STRING Path
     );
 
 extern VOID
@@ -45,6 +46,12 @@ RegistryTeardown(
     VOID
     );
 
+extern NTSTATUS
+RegistryOpenParametersKey(
+    IN  ACCESS_MASK     DesiredAccess,
+    OUT PHANDLE         Key
+    );
+
 extern NTSTATUS
 RegistryOpenKey(
     IN  HANDLE          Parent,
diff --git a/src/xen/driver.c b/src/xen/driver.c
index 8fe6c5c..e04a772 100644
--- a/src/xen/driver.c
+++ b/src/xen/driver.c
@@ -515,7 +515,7 @@ DllInitialize(
     if (!NT_SUCCESS(status))
         goto fail1;
 
-    status = RegistryInitialize(RegistryPath);
+    status = RegistryInitialize(NULL, RegistryPath);
     if (!NT_SUCCESS(status))
         goto fail2;
 
diff --git a/src/xenbus/driver.c b/src/xenbus/driver.c
index 522acef..d6efe89 100644
--- a/src/xenbus/driver.c
+++ b/src/xenbus/driver.c
@@ -811,7 +811,6 @@ DriverEntry(
     IN  PUNICODE_STRING RegistryPath
     )
 {
-    HANDLE              ServiceKey;
     HANDLE              ParametersKey;
     ULONG               Index;
     LOG_LEVEL           LogLevel;
@@ -839,21 +838,14 @@ DriverEntry(
          MONTH,
          YEAR);
 
-    status = RegistryInitialize(RegistryPath);
+    status = RegistryInitialize(DriverObject, RegistryPath);
     if (!NT_SUCCESS(status))
         goto fail1;
 
-    status = RegistryOpenServiceKey(KEY_READ, &ServiceKey);
+    status = RegistryOpenParametersKey(KEY_READ, &ParametersKey);
     if (!NT_SUCCESS(status))
         goto fail2;
 
-    status = RegistryOpenSubKey(ServiceKey,
-                                "Parameters",
-                                KEY_READ,
-                                &ParametersKey);
-    if (!NT_SUCCESS(status))
-        goto fail3;
-
     __DriverSetParametersKey(ParametersKey);
 
     status = LogReadLogLevel(ParametersKey,
@@ -864,8 +856,6 @@ DriverEntry(
 
     __DriverSetConsoleLogLevel(LogLevel);
 
-    RegistryCloseKey(ServiceKey);
-
     status = XenTouch(__MODULE__,
                       MAJOR_VERSION,
                       MINOR_VERSION,
@@ -900,11 +890,6 @@ done:
 
     return STATUS_SUCCESS;
 
-fail3:
-    Error("fail3\n");
-
-    RegistryCloseKey(ServiceKey);
-
 fail2:
     Error("fail2\n");
 
diff --git a/src/xenfilt/driver.c b/src/xenfilt/driver.c
index 724d418..aee663a 100644
--- a/src/xenfilt/driver.c
+++ b/src/xenfilt/driver.c
@@ -113,33 +113,6 @@ DriverGetDriverObject(
     return __DriverGetDriverObject();
 }
 
-static FORCEINLINE NTSTATUS
-__DriverOpenParametersKey(
-    OUT PHANDLE     ParametersKey
-    )
-{
-    HANDLE          ServiceKey;
-    NTSTATUS        status;
-
-    status = RegistryOpenServiceKey(KEY_READ, &ServiceKey);
-    if (!NT_SUCCESS(status))
-        goto fail1;
-
-    status = RegistryOpenSubKey(ServiceKey, "Parameters", KEY_READ, 
ParametersKey);
-    if (!NT_SUCCESS(status))
-        goto fail2;
-
-    RegistryCloseKey(ServiceKey);
-
-    return STATUS_SUCCESS;
-
-fail2:
-    RegistryCloseKey(ServiceKey);
-
-fail1:
-    return status;
-}
-
 static FORCEINLINE VOID
 __DriverSetEmulatedContext(
     IN  PXENFILT_EMULATED_CONTEXT   Context
@@ -247,7 +220,7 @@ __DriverGetActive(
 
     ASSERT3U(KeGetCurrentIrql(), ==, PASSIVE_LEVEL);
 
-    status = __DriverOpenParametersKey(&ParametersKey);
+    status = RegistryOpenParametersKey(KEY_READ, &ParametersKey);
     if (!NT_SUCCESS(status))
         goto fail1;
 
@@ -752,7 +725,7 @@ DriverGetEmulatedType(
     ULONG                           Index;
     NTSTATUS                        status;
 
-    status = __DriverOpenParametersKey(&ParametersKey);
+    status = RegistryOpenParametersKey(KEY_READ, &ParametersKey);
     if (!NT_SUCCESS(status))
         goto fail1;
 
@@ -947,7 +920,7 @@ DriverEntry(
     if (!NT_SUCCESS(status))
         goto done;
 
-    status = RegistryInitialize(RegistryPath);
+    status = RegistryInitialize(DriverObject, RegistryPath);
     if (!NT_SUCCESS(status))
         goto fail1;
 
-- 
2.44.0.windows.1