pcapif: add option PCAPIF_RX_READONLY to simulate readonly RX

This uses VirtualAlloc/VirtualProtect on windows to simulate RX buffers
that are readonly to lwIP (see task #14807).

Signed-off-by: Simon Goldschmidt <goldsimon@gmx.de>

contrib/ports/win32/pcapif.c

@@ -113,6 +113,8 @@
 
 /** If 1, use PBUF_REF for RX (for testing purposes mainly).
  * For this, LWIP_SUPPORT_CUSTOM_PBUF must be enabled.
+ * Also, PBUF_POOL_BUFSIZE must be set high enough to ensure all rx packets
+ * fit into a single pbuf.
  */
 #ifndef PCAPIF_RX_REF
 #define PCAPIF_RX_REF                 0
@@ -127,6 +129,13 @@
 #define PCAPIF_GET_STATE_PTR(netif)   ((netif)->state)
 #endif
 
+/** Define this to 1 to allocate readonly pbufs for RX (needs PCAPIF_RX_REF,
+ * only implemented for windows, for now)
+ */
+#ifndef PCAPIF_RX_READONLY
+#define PCAPIF_RX_READONLY            0
+#endif
+
 #if PCAPIF_HANDLE_LINKSTATE
 #include "pcapif_helper.h"
 
@@ -320,7 +329,11 @@ pcaipf_is_tx_packet(struct netif *netif, const void *packet, int packet_len)
 struct pcapif_pbuf_custom
 {
    struct pbuf_custom pc;
+#if PCAPIF_RX_READONLY
+   void *ro_mem;
+#else
    struct pbuf* p;
+#endif
 };
 #endif /* PCAPIF_RX_REF */
 
@@ -961,9 +974,15 @@ pcapif_rx_pbuf_free_custom(struct pbuf *p)
   struct pcapif_pbuf_custom* ppc;
   LWIP_ASSERT("NULL pointer", p != NULL);
   ppc = (struct pcapif_pbuf_custom*)p;
+#if PCAPIF_RX_READONLY
+  LWIP_ASSERT("NULL pointer", ppc->ro_mem != NULL);
+  pcapifh_free_readonly_mem(ppc->ro_mem);
+  ppc->ro_mem = NULL;
+#else
   LWIP_ASSERT("NULL pointer", ppc->p != NULL);
   pbuf_free(ppc->p);
   ppc->p = NULL;
+#endif
   mem_free(p);
 }
 
@@ -972,6 +991,8 @@ pcapif_rx_ref(struct pbuf* p)
 {
   struct pcapif_pbuf_custom* ppc;
   struct pbuf* q;
+  u16_t len;
+  void *payload_mem;
 
   LWIP_ASSERT("NULL pointer", p != NULL);
   LWIP_ASSERT("chained pbuf not supported here", p->next == NULL);
@@ -979,9 +1000,18 @@ pcapif_rx_ref(struct pbuf* p)
   ppc = (struct pcapif_pbuf_custom*)mem_malloc(sizeof(struct pcapif_pbuf_custom));
   LWIP_ASSERT("out of memory for RX", ppc != NULL);
   ppc->pc.custom_free_function = pcapif_rx_pbuf_free_custom;
+  len = p->tot_len;
+#if PCAPIF_RX_READONLY
+  payload_mem = pcapifh_alloc_readonly_copy(p->payload, len);
+  LWIP_ASSERT("out of readonly memory for RX", payload_mem != NULL);
+  pbuf_free(p);
+  ppc->ro_mem = payload_mem;
+#else
   ppc->p = p;
+  payload_mem = p->payload;
+#endif
 
-  q = pbuf_alloced_custom(PBUF_RAW, p->tot_len, PBUF_REF, &ppc->pc, p->payload, p->tot_len);
+  q = pbuf_alloced_custom(PBUF_RAW, len, PBUF_REF, &ppc->pc, payload_mem, len);
   LWIP_ASSERT("pbuf_alloced_custom returned NULL", q != NULL);
   return q;
 }

contrib/ports/win32/pcapif_helper.c

@@ -78,6 +78,43 @@ void pcapifh_linkstate_close(struct pcapifh_linkstate* state)
   }
 }
 
+/** Helper function for PCAPIF_RX_READONLY for windows: copy the date to a new
+ * page which is set to READONLY after copying.
+ * This is a helper to simulate hardware that receives to memory that cannot be
+ * written by the CPU.
+ */
+void *
+pcapifh_alloc_readonly_copy(void *data, size_t len)
+{
+  DWORD oldProtect;
+  void *ret;
+  if (len > 4096) {
+    lwip_win32_platform_diag("pcapifh_alloc_readonly_copy: invalid len: %d\n", len);
+    while(1);
+  }
+  ret = VirtualAlloc(NULL, 4096, MEM_COMMIT, PAGE_READWRITE);
+  if (ret == NULL) {
+    lwip_win32_platform_diag("VirtualAlloc failed: %d\n", GetLastError());
+    while(1);
+  }
+  memcpy(ret, data, len);
+  if (!VirtualProtect(ret, len, PAGE_READONLY, &oldProtect)) {
+    lwip_win32_platform_diag("VirtualProtect failed: %d\n", GetLastError());
+    while(1);
+  }
+  printf("pcapifh_alloc_readonly_copy(%d): 0x%08x\n", len, ret);
+  return ret;
+}
+
+void
+pcapifh_free_readonly_mem(void *data)
+{
+  if (!VirtualFree(data, 0, MEM_RELEASE)) {
+    lwip_win32_platform_diag("VirtualFree(0x%08x) failed: %d\n", data, GetLastError());
+    while(1);
+  }
+}
+
 #else /* WIN32 */
 
 /* @todo: add linux/unix implementation? */

contrib/ports/win32/pcapif_helper.h

@@ -1,6 +1,8 @@
 #ifndef LWIP_PCAPIF_HELPER_H
 #define LWIP_PCAPIF_HELPER_H
 
+#include <stddef.h>
+
 #ifdef __cplusplus
 extern "C" {
 #endif
@@ -17,6 +19,8 @@ struct pcapifh_linkstate* pcapifh_linkstate_init(char *adapter_name);
 enum pcapifh_link_event pcapifh_linkstate_get(struct pcapifh_linkstate* state);
 void pcapifh_linkstate_close(struct pcapifh_linkstate* state);
 
+void *pcapifh_alloc_readonly_copy(void *data, size_t len);
+void pcapifh_free_readonly_mem(void *data);
 
 #ifdef __cplusplus
 }