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sel4: testing the unwrapping of capabilities

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This commit is contained in:
Norman Feske 2015-02-10 16:18:20 +01:00 committed by Christian Helmuth
parent 33c2bc3bf2
commit 418f2ab119
2 changed files with 107 additions and 19 deletions
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45
repos/base-sel4/doc/ipc_and_virt_mem.txt
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@ -185,6 +185,51 @@ single RPC call.
That said, the simple capability-delegation test works as expected.
Translation of capabilities aka "unwrapping"
============================================
In addition to receiving delegated capabilities under a new name, seL4's IPC
mechanism allows the recipient of a capability that originated from the
recipient to obtain a custom defined value instead of receiving a new name.
In seL4 terminology, this mechanism is called "unwrapping".
Capability unwrapping is supposed to happen if the transferred capability is
a minted endpoint capability and the recipient is the original creator of
the capability. For testing the mechanism, we replace the 'SECOND_THREAD_CAP'
argument of the 'seL4_Call' by a minted endpoint capability derived from
the endpoint used by the second thread.
For creating a minted endpoint capability, we allocate a new index for the
minted capability (EP_MINTED_CAP) and use the 'seL4_CNode_Mint' operation
as follows:
! seL4_CNode const service = seL4_CapInitThreadCNode;
! seL4_Word const dest_index = EP_MINTED_CAP;
! uint8_t const dest_depth = 32;
! seL4_CNode const src_root = seL4_CapInitThreadCNode;
! seL4_Word const src_index = EP_CAP;
! uint8_t const src_depth = 32;
! seL4_CapRights const rights = seL4_Transfer_Mint;
! seL4_CapData_t const badge = seL4_CapData_Badge_new(111);
!
! int const ret = seL4_CNode_Mint(service,
! dest_index,
! dest_depth,
! src_root,
! src_index,
! src_depth,
! rights,
! badge);
The badge is set to the magic value 111.
When specifying the resulting EP_MINTED_CAP as IPC argument for a 'seL4_Call',
the kernel will translate the capability to the badge value. The callee
observes the reception of such an "unwrapped" capability via the
'capsUnwrapped' field of the 'seL4_MessageInfo' structure returned by the
'seL4_Wait' operation. The badge value can be obtained from the IPC buffer via
'seL4_GetBadge(0)'. This simple experiment shows that the mechanism works
as expected.

81
repos/base-sel4/src/test/sel4/main.cc
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@ -87,29 +87,34 @@ enum { EP_CAP = 0x101 };
*/
enum { RECV_CAP = 0x102 };
/*
* Minted endpoint capability, derived from EP_CAP
*/
enum { EP_MINTED_CAP = 0x103 };
void second_thread_entry()
{
init_ipc_buffer();
seL4_SetCapReceivePath(seL4_CapInitThreadCNode, RECV_CAP, 32);
for (;;) {
seL4_SetCapReceivePath(seL4_CapInitThreadCNode, RECV_CAP, 32);
PDBG("call seL4_Wait");
seL4_MessageInfo_t msg_info = seL4_Wait(EP_CAP, nullptr);
PDBG("returned from seL4_Wait, call seL4_Reply");
PDBG("call seL4_Wait");
seL4_MessageInfo_t msg_info = seL4_Wait(EP_CAP, nullptr);
PDBG("returned from seL4_Wait, call seL4_Reply");
PDBG("msg_info: got unwrapped %d", seL4_MessageInfo_get_capsUnwrapped(msg_info));
PDBG(" got extra caps %d", seL4_MessageInfo_get_extraCaps(msg_info));
PDBG(" label %d", seL4_MessageInfo_get_label(msg_info));
PDBG("msg_info: got unwrapped %d", seL4_MessageInfo_get_capsUnwrapped(msg_info));
PDBG(" got extra caps %d", seL4_MessageInfo_get_extraCaps(msg_info));
PDBG(" label %d", seL4_MessageInfo_get_label(msg_info));
seL4_TCB_Suspend(RECV_CAP);
if (seL4_MessageInfo_get_capsUnwrapped(msg_info)) {
PDBG(" badge %d", seL4_CapData_Badge_get_Badge(seL4_GetBadge(0)));
}
PDBG("this message should not appear");
seL4_Reply(msg_info);
PDBG("returned from seL4_Reply");
*(int *)0x2244 = 0;
seL4_Reply(msg_info);
PDBG("returned from seL4_Reply");
}
}
@ -225,15 +230,53 @@ int main()
seL4_TCB_SetPriority(SECOND_THREAD_CAP, 0xff);
PDBG("call seL4_Call");
PDBG("seL4_Call, delegating a TCB capability");
{
seL4_MessageInfo_t msg_info = seL4_MessageInfo_new(13, 0, 1, 0);
seL4_MessageInfo_t msg_info = seL4_MessageInfo_new(13, 0, 1, 0);
seL4_SetCap(0, SECOND_THREAD_CAP);
seL4_SetCap(0, SECOND_THREAD_CAP);
seL4_Call(EP_CAP, msg_info);
seL4_Call(EP_CAP, msg_info);
PDBG("returned from seL4_Call");
}
PDBG("returned from seL4_Call");
PDBG("seL4_Call, delegating a minted endpoint capability");
{
/* mint EP_CAP into EP_MINTED_CAP */
seL4_CNode const service = seL4_CapInitThreadCNode;
seL4_Word const dest_index = EP_MINTED_CAP;
uint8_t const dest_depth = 32;
seL4_CNode const src_root = seL4_CapInitThreadCNode;
seL4_Word const src_index = EP_CAP;
uint8_t const src_depth = 32;
seL4_CapRights const rights = seL4_Transfer_Mint;
seL4_CapData_t const badge = seL4_CapData_Badge_new(111);
int const ret = seL4_CNode_Mint(service,
dest_index,
dest_depth,
src_root,
src_index,
src_depth,
rights,
badge);
PDBG("seL4_CNode_Mint (EP_MINTED_CAP) returned %d", ret);
seL4_MessageInfo_t msg_info = seL4_MessageInfo_new(13, 0, 3, 0);
/*
* Supply 3 capabilities as arguments. The first and third will be
* unwrapped at the receiver, the second will be delegated.
*/
seL4_SetCap(0, EP_MINTED_CAP);
seL4_SetCap(1, SECOND_THREAD_CAP);
seL4_SetCap(2, EP_MINTED_CAP);
seL4_Call(EP_CAP, msg_info);
PDBG("returned from seL4_Call");
}
*(int *)0x1122 = 0;
return 0;