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base: fix dangling session pointers in rm_session 

If page faults are handled concurrently (as for base-nova) the traverse lookup
call in rm_session_component must be thread safe, which it isn't.
If the faulting area is backed by nested dataspaces which are managed by
various rm_sessions then a race happens under following circumstances
(triggered occasionally by the bomb test).

The traverse lookup may return a pointer to a rm_session of a nested dataspace.
If the rm_session is in parallel subject to destruction it happened that faults
got enqueued to the faulters list of the deleted rm_session and internally to
a list of the current rm_session of the Rm_client.

During destruction of the faulting Rm_client the associated rm_session will
be dissolved from the Rm_client, which leads to dereferencing the
dangling pointer of the already destructed rm_session.

On base-nova the memory of the rm_session object get unmapped eventually, so
that the de-referencing of the dangling pointer caused page faults in core.

The memory on other kernels inside core never get unmapped so that the
bug doesn't trigger visible faults.

The patch replace the keeping of a rm_session pointer by keeping a
capability instead. The rm_session object must be looked up now explicitly in
the Object_pool implementation, which implements proper reference counting on
the rm_session object.

Issue #549
This commit is contained in:
Alexander Boettcher 2012-12-14 09:29:49 +01:00 committed by Norman Feske
parent 08d87adb4b
commit f50d816555
5 changed files with 100 additions and 29 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

12
base-linux/src/core/include/rm_session_component.h
View File

@ -28,10 +28,20 @@ namespace Genode {
class Rm_session_component : public Rpc_object<Rm_session>
{
private:
class Rm_dataspace_component {
public:
void sub_rm_session(Native_capability _cap) { }
};
public:
Rm_session_component(Rpc_entrypoint *ds_ep,
Rpc_entrypoint *thread_ep,
Rpc_entrypoint *session_ep,
Allocator *md_alloc,
size_t ram_quota,
Pager_entrypoint *pager_ep,
@ -56,7 +66,7 @@ namespace Genode {
Dataspace_capability dataspace() { return Dataspace_capability(); }
void dissolve(Rm_client *cl) { }
Rm_dataspace_component *dataspace_component() { return 0; }
};
struct Rm_member { Rm_session_component *member_rm_session() { return 0; } };

5
base/src/core/include/dataspace_component.h
View File

@ -27,7 +27,6 @@
namespace Genode {
class Rm_region;
class Rm_session_component;
/**
* Deriving classes can own a dataspace to implement conditional behavior
@ -117,9 +116,9 @@ namespace Genode {
/**
* Return region-manager session corresponding to nested dataspace
*
* \retval 0 dataspace is not a nested dataspace
* \retval invalid capability if dataspace is not a nested one
*/
virtual Rm_session_component *sub_rm_session() { return 0; }
virtual Native_capability sub_rm_session() { return Dataspace_capability(); }
addr_t core_local_addr() const { return _core_local_addr; }
bool is_io_mem() const { return _is_io_mem; }

27
base/src/core/include/rm_root.h
View File

@ -49,10 +49,31 @@ namespace Genode {
return new (md_alloc())
Rm_session_component(_ds_ep,
_thread_ep,
this->ep(),
_md_alloc, ram_quota,
&_pager_ep,
start == ~0UL ? _vm_start : start,
size == 0 ? _vm_size : size);
&_pager_ep,
start == ~0UL ? _vm_start : start,
size == 0 ? _vm_size : size);
}
Session_capability session(Root::Session_args const &args)
{
Session_capability cap = Root_component<Rm_session_component>::session(args);
/* lookup rm_session_component object */
Object_pool<Rm_session_component>::Guard rm_session(ep()->lookup_and_lock(cap));
if (!rm_session)
/* should never happen */
return cap;
/**
* Assign rm_session capability to dataspace component. It can
* not be done beforehand because the dataspace_component is
* constructed before the rm_session
*/
if (rm_session->dataspace_component())
rm_session->dataspace_component()->sub_rm_session(rm_session->cap());
return cap;
}
void _upgrade_session(Rm_session_component *rm, const char *args)

22
base/src/core/include/rm_session_component.h
View File

@ -212,6 +212,7 @@ namespace Genode {
Rpc_entrypoint *_ds_ep;
Rpc_entrypoint *_thread_ep;
Rpc_entrypoint *_session_ep;
Allocator_guard _md_alloc;
Signal_transmitter _fault_notifier; /* notification mechanism for
@ -239,24 +240,25 @@ namespace Genode {
{
private:
Rm_session_component *_rm_session_component;
Native_capability _rm_session_cap;
public:
/**
* Constructor
*/
Rm_dataspace_component(Rm_session_component *rsc, size_t size)
Rm_dataspace_component(size_t size)
:
Dataspace_component(size, 0, false, false, 0),
_rm_session_component(rsc) { _managed = true; }
Dataspace_component(size, 0, false, false, 0)
{ _managed = true; }
/***********************************
** Dataspace component interface **
***********************************/
Rm_session_component *sub_rm_session() { return _rm_session_component; }
Native_capability sub_rm_session() { return _rm_session_cap; }
void sub_rm_session(Native_capability _cap) { _rm_session_cap = _cap; }
};
@ -286,6 +288,7 @@ namespace Genode {
*/
Rm_session_component(Rpc_entrypoint *ds_ep,
Rpc_entrypoint *thread_ep,
Rpc_entrypoint *session_ep,
Allocator *md_alloc,
size_t ram_quota,
Pager_entrypoint *pager_ep,
@ -301,10 +304,11 @@ namespace Genode {
*
* \return true lookup succeeded
*/
bool reverse_lookup(addr_t dst_base,
Fault_area *dst_fault_region,
Dataspace_component **src_dataspace,
Fault_area *src_fault_region);
bool reverse_lookup(addr_t dst_base,
Fault_area *dst_fault_region,
Dataspace_component **src_dataspace,
Fault_area *src_fault_region,
Rm_session_component **sub_rm_session);
/**
* Register fault

63
base/src/core/rm_session_component.cc
View File

@ -2,6 +2,7 @@
* \brief Implementation of the RM session interface
* \author Christian Helmuth
* \author Norman Feske
* \author Alexander Boettcher
* \date 2006-07-17
*
* FIXME arg_string and quota missing
@ -173,34 +174,59 @@ int Rm_client::pager(Ipc_pager &pager)
print_page_fault("page fault", pf_addr, pf_ip, pf_type, badge());
Rm_session_component *curr_rm_session = member_rm_session();
addr_t curr_rm_base = 0;
Dataspace_component *src_dataspace = 0;
Rm_session_component *sub_rm_session = 0;
addr_t curr_rm_base = 0;
Dataspace_component *src_dataspace = 0;
Rm_session_component::Fault_area src_fault_area;
Rm_session_component::Fault_area dst_fault_area(pf_addr);
bool lookup;
/* traverse potentially nested dataspaces until we hit a leaf dataspace */
unsigned level;
enum { MAX_NESTING_LEVELS = 5 };
for (level = 0; level < MAX_NESTING_LEVELS; level++) {
/* helper guard to release the rm_session lock on return */
class Guard {
private:
Rm_session_component ** _release_session;
unsigned * _level;
public:
explicit Guard(Rm_session_component ** rs, unsigned * level)
: _release_session(rs), _level(level) {}
~Guard() {
if ((*_level > 0) && (*_release_session))
(*_release_session)->release();
}
} release_guard(&curr_rm_session, &level);
/* traverse potentially nested dataspaces until we hit a leaf dataspace */
for (level = 0; level < MAX_NESTING_LEVELS; level++) {
lookup = curr_rm_session->reverse_lookup(curr_rm_base,
&dst_fault_area,
&src_dataspace,
&src_fault_area);
if (!lookup)
break;
&src_fault_area,
&sub_rm_session);
/* check if we need to traverse into a nested dataspace */
Rm_session_component *sub_rm_session = src_dataspace->sub_rm_session();
if (!sub_rm_session)
break;
if (!lookup) {
sub_rm_session->release();
break;
}
/* set up next iteration */
curr_rm_base = dst_fault_area.fault_addr()
- src_fault_area.fault_addr() + src_dataspace->map_src_addr();
if (level > 0)
curr_rm_session->release();
curr_rm_session = sub_rm_session;
sub_rm_session = 0;
}
if (level == MAX_NESTING_LEVELS) {
@ -624,7 +650,8 @@ void Rm_session_component::remove_client(Pager_capability pager_cap)
bool Rm_session_component::reverse_lookup(addr_t dst_base,
Fault_area *dst_fault_area,
Dataspace_component **src_dataspace,
Fault_area *src_fault_area)
Fault_area *src_fault_area,
Rm_session_component **sub_rm_session)
{
/* serialize access */
Lock::Guard lock_guard(_lock);
@ -672,7 +699,16 @@ bool Rm_session_component::reverse_lookup(addr_t dst_base,
/* constrain source fault area by the source dataspace dimensions */
src_fault_area->constrain(src_base, (*src_dataspace)->size());
return src_fault_area->valid() && dst_fault_area->valid();
bool lookup = src_fault_area->valid() && dst_fault_area->valid();
if (!lookup)
return lookup;
/* lookup and lock nested dataspace if required */
Native_capability session_cap = (*src_dataspace)->sub_rm_session();
*sub_rm_session = dynamic_cast<Rm_session_component *>(_session_ep->lookup_and_lock(session_cap));
return lookup;
}
@ -732,17 +768,18 @@ static Dataspace_capability _type_deduction_helper(Dataspace_capability cap) {
Rm_session_component::Rm_session_component(Rpc_entrypoint *ds_ep,
Rpc_entrypoint *thread_ep,
Rpc_entrypoint *session_ep,
Allocator *md_alloc,
size_t ram_quota,
Pager_entrypoint *pager_ep,
addr_t vm_start,
size_t vm_size)
:
_ds_ep(ds_ep), _thread_ep(thread_ep),
_ds_ep(ds_ep), _thread_ep(thread_ep), _session_ep(session_ep),
_md_alloc(md_alloc, ram_quota),
_client_slab(&_md_alloc), _ref_slab(&_md_alloc),
_map(&_md_alloc), _pager_ep(pager_ep),
_ds(this, vm_size), _ds_cap(_type_deduction_helper(ds_ep->manage(&_ds)))
_ds(vm_size), _ds_cap(_type_deduction_helper(ds_ep->manage(&_ds)))
{
/* configure managed VM area */
_map.add_range(vm_start, vm_size);