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L4Re Operating System Framework
Interface and Usage Documentation
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L4Re Operating System Framework
Interface and Usage Documentation
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The C++ IPC gate interface, see IPC-Gate API for the C interface. More...
#include <ipc_gate>
Inheritance diagram for L4::Ipc_gate: Collaboration diagram for L4::Ipc_gate:Public Member Functions | |
| l4_msgtag_t | get_infos (l4_umword_t *label) |
| Get information about the IPC-gate. | |
| Public Member Functions inherited from L4::Rcv_endpoint | |
| l4_msgtag_t | bind_thread (Ipc::Cap< Thread > t, l4_umword_t label) |
| Bind the IPC receive endpoint to a thread. | |
| Public Member Functions inherited from L4::Kobject | |
| l4_msgtag_t | dec_refcnt (l4_mword_t diff, l4_utcb_t *utcb=l4_utcb()) |
| Decrement the in kernel reference counter for the object. | |
Additional Inherited Members | |
| Protected Types inherited from L4::Kobject_t< Ipc_gate, Rcv_endpoint, L4_PROTO_KOBJECT, Type_info::Demand_t< 1 > > | |
| typedef Ipc_gate | Class |
| The target interface type (inheriting from Kobject_t) | |
| typedef Typeid::Iface< PROTO, Ipc_gate > | __Iface |
| The interface description for the derived class. | |
| typedef Typeid::Merge_list< Typeid::Iface_list< __Iface >, typename Base::__Iface_list > | __Iface_list |
| The list of all RPC interfaces provided directly or through inheritance. | |
| Protected Types inherited from L4::Kobject_t< Rcv_endpoint, Kobject, L4_PROTO_KOBJECT, Type_info::Demand_t< 1 > > | |
| typedef Rcv_endpoint | Class |
| The target interface type (inheriting from Kobject_t) | |
| typedef Typeid::Iface< PROTO, Rcv_endpoint > | __Iface |
| The interface description for the derived class. | |
| typedef Typeid::Merge_list< Typeid::Iface_list< __Iface >, typename Base::__Iface_list > | __Iface_list |
| The list of all RPC interfaces provided directly or through inheritance. | |
| Protected Member Functions inherited from L4::Kobject_t< Ipc_gate, Rcv_endpoint, L4_PROTO_KOBJECT, Type_info::Demand_t< 1 > > | |
| L4::Cap< Class > | c () const noexcept |
| Get the capability to ourselves. | |
| Protected Member Functions inherited from L4::Kobject_t< Rcv_endpoint, Kobject, L4_PROTO_KOBJECT, Type_info::Demand_t< 1 > > | |
| L4::Cap< Class > | c () const noexcept |
| Get the capability to ourselves. | |
| Protected Member Functions inherited from L4::Kobject | |
| l4_cap_idx_t | cap () const noexcept |
| Return capability selector. | |
| Static Protected Member Functions inherited from L4::Kobject_t< Ipc_gate, Rcv_endpoint, L4_PROTO_KOBJECT, Type_info::Demand_t< 1 > > | |
| static void | __check_protocols__ () noexcept |
| Helper to check for protocol conflicts. | |
| Static Protected Member Functions inherited from L4::Kobject_t< Rcv_endpoint, Kobject, L4_PROTO_KOBJECT, Type_info::Demand_t< 1 > > | |
| static void | __check_protocols__ () noexcept |
| Helper to check for protocol conflicts. | |
The C++ IPC gate interface, see IPC-Gate API for the C interface.
IPC gates are used to create secure communication channels between protection domains. An IPC gate can be created using the L4::Factory interface.
Depending on the permissions of the capability used, an IPC gate forwards IPC to the L4::Thread the IPC gate is bound to (cf. bind_thread()). If the capability has the L4_FPAGE_C_IPCGATE_SVR permission, only IPC using a protocol different from the L4_PROTO_KOBJECT protocol is forwarded. Without the L4_FPAGE_C_IPCGATE_SVR permission, all IPC is forwarded. The latter is the usual case for a client in a client/server scenario. When not bound to a thread yet, the forwarded IPC blocks until the IPC gate is bound to a thread or the IPC times out.
Forwarded IPC is always forwarded to the userland of the thread the IPC gate is bound to. That means, the L4::Thread interface of that thread is not accessible via an IPC gate. The L4::Ipc_gate interface of an IPC gate is only accessible if the capability used has the L4_FPAGE_C_IPCGATE_SVR permission (cf. previous paragraph). Conversely that means, if the capability used lacks the L4_FPAGE_C_IPCGATE_SVR permission, L4::Ipc_gate interface calls are forwarded to the thread the IPC gate is bound to instead of being processed by the IPC gate itself. In a client/server scenario, a client should only get IPC gate capabilities without L4_FPAGE_C_IPCGATE_SVR permission so the client cannot tamper with the IPC gate.
When binding an IPC gate to a thread, a user-defined, kernel protected, machine-word sized payload called the IPC gate’s label is assigned to the IPC gate (note that the two least significant bits of the label must be zero; cf. bind_thread()). When a send-only IPC or call IPC is forwarded via an IPC gate, the label provided by the sender is ignored and replaced by the IPC gate’s label where the two least significant bits are set to the L4_CAP_FPAGE_S and L4_CAP_FPAGE_W permissions of the capability used. The replaced label is only visible to the thread the IPC gate is bound to upon receive. However, the configured label of an IPC gate can also be queried via get_infos() if the capability used has the L4_FPAGE_C_IPCGATE_SVR permission.
When deleting an IPC gate or when unbinding it from a thread, the label of IPC already in flight won't be changed. To ensure that no IPC from this IPC gate is received by a thread with an unexpected label, L4::Thread::modify_senders() shall be used to change the labels of every pending IPC to that gate. This is also required if the label of an already bound IPC gate is changed. It is not necessary after binding the IPC gate to a thread for the first time.
When binding a currently bound IPC gate to a new thread, the same label should be used that was used with the old thread. Otherwise the old and the new thread need to synchronize to avoid IPC messages with unexpected labels.
For the C interface refer to the C IPC-Gate API.
| l4_msgtag_t L4::Ipc_gate::get_infos | ( | l4_umword_t * | label | ) |
Get information about the IPC-gate.
| [out] | label | The label of the IPC gate is returned here. |
1.9.8