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Session::recreate_shared_mmap fixes #3863

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merged 1 commit into from
Nov 3, 2024
Merged

Session::recreate_shared_mmap fixes #3863

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21 changes: 18 additions & 3 deletions src/Session.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -560,9 +560,22 @@ const AddressSpace::Mapping Session::recreate_shared_mmap(
uint32_t flags = m.flags;
size_t size = m.map.size();
void* preserved_data = preserve == PRESERVE_CONTENTS ? m.local_addr : nullptr;
if (preserved_data) {
remote.task()->vm()->detach_local_mapping(m.map.start());
void* remote_task_local_mapping = nullptr;

{
// Note that Mapping `m` may correspond to a Mapping from a different Task
// than the `maybe_detach_mapping`. See replay_syscall.cc prepare_clone()
// for an example.
auto remote_task_mapping = remote.task()->vm()->mapping_of(m.map.start());

// Sanity check
ASSERT(remote.task(), size == remote_task_mapping.map.size());
ASSERT(remote.task(), m.map.start() == remote_task_mapping.map.start());

remote_task_local_mapping =
remote.task()->vm()->detach_local_mapping(m.map.start());
}

remote_ptr<void> new_addr =
create_shared_mmap(remote, m.map.size(), m.map.start(),
extract_name(name, sizeof(name)), m.map.prot(), 0,
Expand All @@ -575,9 +588,11 @@ const AddressSpace::Mapping Session::recreate_shared_mmap(
new_map = remote.task()->vm()->mapping_of(new_addr);
if (preserved_data) {
memcpy(new_map.local_addr, preserved_data, size);
munmap(preserved_data, size);
}
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This here is very problematic as it could unmap the local memory for the wrong task. We want to unmap for remote.task()Mapping's local_addr and not for Mapping m's local_addr

}
if (remote_task_local_mapping) {
munmap(remote_task_local_mapping, size);
}
return new_map;
}

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