[PATCH gnumach] Consider protected payloads in mach_msg_header_t when resizing messages.

[Flavio Cruz]

Protected payloads will be 8-byte longs which are the same size as
kernel ports.

Also aligned all the structures to be 4-byte aligned since it makes it
easier to parse them as padding won't be added to mach_msg_user_header_t
before the protected payload.
---
 include/mach/message.h |  9 ++++++++-
 x86_64/copy_user.c     | 22 ++++++++++++++++++++++
 2 files changed, 30 insertions(+), 1 deletion(-)

diff --git a/include/mach/message.h b/include/mach/message.h
index 21c551c2..63341e6f 100644
--- a/include/mach/message.h
+++ b/include/mach/message.h
@@ -132,6 +132,9 @@ typedef     unsigned int mach_msg_size_t;
 typedef natural_t mach_msg_seqno_t;
 typedef integer_t mach_msg_id_t;
 
+/* Force 4-byte alignment to simplify how the kernel parses the messages */
+#pragma pack(push, 4)
+
 /* full header structure, may have different size in user/kernel spaces */
 typedef        struct mach_msg_header {
     mach_msg_bits_t    msgh_bits;
@@ -151,7 +154,10 @@ typedef    struct {
     mach_msg_bits_t    msgh_bits;
     mach_msg_size_t    msgh_size;
     mach_port_name_t   msgh_remote_port;
-    mach_port_name_t   msgh_local_port;
+    union {
+        mach_port_name_t       msgh_local_port;
+        rpc_uintptr_t msgh_protected_payload;
+    };
     mach_port_seqno_t  msgh_seqno;
     mach_msg_id_t      msgh_id;
 } mach_msg_user_header_t;
@@ -224,6 +230,7 @@ typedef     struct  {
     natural_t          msgtl_number;
 } mach_msg_type_long_t;
 
+#pragma pack(pop)
 
 /*
  *     Known values for the msgt_name field.
diff --git a/x86_64/copy_user.c b/x86_64/copy_user.c
index b340d6f0..ae062645 100644
--- a/x86_64/copy_user.c
+++ b/x86_64/copy_user.c
@@ -16,6 +16,7 @@
  * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
  */
 
+#include <stddef.h>
 #include <string.h>
 
 #include <kern/debug.h>
@@ -181,8 +182,21 @@ int copyinmsg (const void *userbuf, void *kernelbuf, const 
size_t usize)
   /* kmsg->msgh_size is filled in later */
   if (copyin_port(&umsg->msgh_remote_port, &kmsg->msgh_remote_port))
     return 1;
+#ifdef USER32
+  /* This could contain a payload, but for 32 bits it will be the same size as 
a mach_port_name_t */
+  _Static_assert(sizeof(rpc_uintptr_t) == sizeof(mach_port_name_t),
+                 "rpc_uintptr_t and mach_port_name_t expected to have the same 
size");
   if (copyin_port(&umsg->msgh_local_port, &kmsg->msgh_local_port))
     return 1;
+#else
+  /* For pure 64 bits, the protected payload is as large as a port pointer. */
+  _Static_assert(sizeof(rpc_uintptr_t) == sizeof(mach_port_t),
+                 "rpc_uintptr_t and mach_port_t expected to have the same 
size");
+  if (copyin((char*)umsg + offsetof(mach_msg_user_header_t, msgh_local_port),
+              (char*)kmsg + offsetof(mach_msg_header_t, msgh_local_port),
+             sizeof(rpc_uintptr_t)))
+    return 1;
+#endif
   if (copyin(&umsg->msgh_seqno, &kmsg->msgh_seqno,
              sizeof(kmsg->msgh_seqno) + sizeof(kmsg->msgh_id)))
     return 1;
@@ -275,8 +289,16 @@ int copyoutmsg (const void *kernelbuf, void *userbuf, 
const size_t ksize)
   /* umsg->msgh_size is filled in later */
   if (copyout_port(&kmsg->msgh_remote_port, &umsg->msgh_remote_port))
     return 1;
+#ifdef USER32
   if (copyout_port(&kmsg->msgh_local_port, &umsg->msgh_local_port))
     return 1;
+#else
+  /* Handle protected payloads correctly, same as copyinmsg. */
+  if (copyout((char*)kmsg + offsetof(mach_msg_header_t, msgh_local_port),
+              (char*)umsg + offsetof(mach_msg_user_header_t, msgh_local_port),
+             sizeof(rpc_uintptr_t)))
+    return 1;
+#endif
   if (copyout(&kmsg->msgh_seqno, &umsg->msgh_seqno,
              sizeof(kmsg->msgh_seqno) + sizeof(kmsg->msgh_id)))
     return 1;
-- 
2.39.1