Index: VirtualBox-6.1.34/src/VBox/HostDrivers/VBoxNetFlt/linux/VBoxNetFlt-linux.c
===================================================================
--- VirtualBox-6.1.34.orig/src/VBox/HostDrivers/VBoxNetFlt/linux/VBoxNetFlt-linux.c
+++ VirtualBox-6.1.34/src/VBox/HostDrivers/VBoxNetFlt/linux/VBoxNetFlt-linux.c
@@ -2311,7 +2311,13 @@ int  vboxNetFltPortOsXmit(PVBOXNETFLTINS
                 vboxNetFltDumpPacket(pSG, true, "host", (fDst & INTNETTRUNKDIR_WIRE) ? 0 : 1);
                 Log6(("vboxNetFltPortOsXmit: pBuf->cb dump:\n%.*Rhxd\n", sizeof(pBuf->cb), pBuf->cb));
                 Log6(("vboxNetFltPortOsXmit: netif_rx_ni(%p)\n", pBuf));
+#if RTLNX_VER_MIN(5,18,0)
+                local_bh_disable();
+                err = netif_rx(pBuf);
+                local_bh_enable();
+#else
                 err = netif_rx_ni(pBuf);
+#endif
                 if (err)
                     rc = RTErrConvertFromErrno(err);
             }
Index: VirtualBox-6.1.34/src/VBox/HostDrivers/Support/SUPDrv.cpp
===================================================================
--- VirtualBox-6.1.34.orig/src/VBox/HostDrivers/Support/SUPDrv.cpp
+++ VirtualBox-6.1.34/src/VBox/HostDrivers/Support/SUPDrv.cpp
@@ -1742,7 +1742,15 @@ static int supdrvIOCtlInnerUnrestricted(
 
             /* execute */
             pReq->u.Out.cFunctions = RT_ELEMENTS(g_aFunctions);
+
+            /* In 5.18.0, memcpy became a wrapper which does fortify checks
+             * before triggering __underlying_memcpy() call. We do not pass these checks here,
+             * so bypass them for now.  */
+#if RTLNX_VER_MIN(5,18,0)
+             __underlying_memcpy(&pReq->u.Out.aFunctions[0], g_aFunctions, sizeof(g_aFunctions));
+#else
             memcpy(&pReq->u.Out.aFunctions[0], g_aFunctions, sizeof(g_aFunctions));
+#endif
             pReq->Hdr.rc = VINF_SUCCESS;
             return 0;
         }
Index: VirtualBox-6.1.34/src/VBox/HostDrivers/Support/SUPLib.cpp
===================================================================
--- VirtualBox-6.1.34.orig/src/VBox/HostDrivers/Support/SUPLib.cpp
+++ VirtualBox-6.1.34/src/VBox/HostDrivers/Support/SUPLib.cpp
@@ -505,7 +505,7 @@ static int supInitFake(PSUPDRVSESSION *p
     if (g_pSupFunctions)
     {
         g_pSupFunctions->u.Out.cFunctions = RT_ELEMENTS(s_aFakeFunctions);
-        memcpy(&g_pSupFunctions->u.Out.aFunctions[0], &s_aFakeFunctions[0], sizeof(s_aFakeFunctions));
+	memcpy(&g_pSupFunctions->u.Out.aFunctions, &s_aFakeFunctions[0], sizeof(s_aFakeFunctions));
         g_pSession = (PSUPDRVSESSION)(void *)g_pSupFunctions;
         if (ppSession)
             *ppSession = g_pSession;
Index: VirtualBox-6.1.34/src/VBox/Additions/linux/sharedfolders/regops.c
===================================================================
--- VirtualBox-6.1.34.orig/src/VBox/Additions/linux/sharedfolders/regops.c
+++ VirtualBox-6.1.34/src/VBox/Additions/linux/sharedfolders/regops.c
@@ -3823,7 +3823,9 @@ struct address_space_operations vbsf_reg
     .readpage       = vbsf_readpage,
     .writepage      = vbsf_writepage,
     /** @todo Need .writepages if we want msync performance...  */
-#if RTLNX_VER_MIN(2,5,12)
+#if RTLNX_VER_MIN(5,18,0)
+    .dirty_folio    = block_dirty_folio,
+#elif RTLNX_VER_MIN(2,5,12)
     .set_page_dirty = __set_page_dirty_buffers,
 #endif
 #if RTLNX_VER_MIN(5,14,0)
Index: VirtualBox-6.1.34/Config.kmk
===================================================================
--- VirtualBox-6.1.34.orig/Config.kmk
+++ VirtualBox-6.1.34/Config.kmk
@@ -4502,11 +4502,14 @@ ifeq ($(VBOX_LDR_FMT),elf)
 TEMPLATE_VBoxR0_TOOL                = $(VBOX_GCC_TOOL)
 TEMPLATE_VBoxR0_CFLAGS              = -fno-pie -nostdinc -g $(VBOX_GCC_pipe) $(VBOX_GCC_WERR) $(VBOX_GCC_PEDANTIC_C) \
 	$(VBOX_GCC_Wno-variadic-macros) $(VBOX_GCC_R0_OPT) $(VBOX_GCC_R0_FP) -fno-strict-aliasing -fno-exceptions \
-	$(VBOX_GCC_fno-stack-protector) -fno-common $(VBOX_GCC_fvisibility-hidden) -std=gnu99 $(VBOX_GCC_IPRT_FMT_CHECK)
+	$(VBOX_GCC_fno-stack-protector) -fno-common -ffreestanding $(VBOX_GCC_fvisibility-hidden) -std=gnu99 $(VBOX_GCC_IPRT_FMT_CHECK)
 TEMPLATE_VBoxR0_CXXFLAGS            = -fno-pie -nostdinc -g $(VBOX_GCC_pipe) $(VBOX_GCC_WERR) $(VBOX_GCC_PEDANTIC_CXX) \
 	$(VBOX_GCC_Wno-variadic-macros) $(VBOX_GCC_R0_OPT) $(VBOX_GCC_R0_FP) -fno-strict-aliasing -fno-exceptions \
 	$(VBOX_GCC_fno-stack-protector) -fno-common $(VBOX_GCC_fvisibility-inlines-hidden) $(VBOX_GCC_fvisibility-hidden) \
 	-fno-rtti $(VBOX_GCC_IPRT_FMT_CHECK)
+ if $(VBOX_GCC_VERSION_CC) >= 40500 # 4.1.2 complains, 4.5.2 is okay, didn't check which version inbetween made it okay with g++.
+	TEMPLATE_VBoxR0_CXXFLAGS           += -ffreestanding
+ endif
 TEMPLATE_VBoxR0_CFLAGS.amd64        = -m64 -mno-red-zone -mno-sse -mno-mmx -mno-sse2 -mno-3dnow -fasynchronous-unwind-tables -ffreestanding
 TEMPLATE_VBoxR0_CXXFLAGS.amd64      = -m64 -mno-red-zone -mno-sse -mno-mmx -mno-sse2 -mno-3dnow -fasynchronous-unwind-tables
 TEMPLATE_VBoxR0_CXXFLAGS.freebsd    = -ffreestanding