[lldb] [debugserver] Shut down the exception thread when clearing #70979
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MachProcess has a MachTask as an ivar. In the MachProcess dtor, we call MachTask::Clear() to clear its state, before running the dtor of all our ivars, including the MachTask one. When we attach on darwin, MachProcess calls MachTask::StartExceptionThread which does the task_for_pid and then starts a thread to listen for mach messages. Then MachProcess calls ptrace(PT_ATTACHEXC). If that ptrace() fails, MachProcess will call MachTask::Clear. But the exception thread is now up & running and is not stopped; its ivars will be reset by the Clear() method, and its object will be freed after the dtor runs. Actually eliciting a crash in this scenario is very timing sensitive; I hand-modified debugserver to fail to PT_ATTACHEXC trying to simulate it on my desktop and was unable. But looking at the source, and an occasional crash report we've received, it's clear that this is possible. rdar://117521198
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@llvm/pr-subscribers-lldb Author: Jason Molenda (jasonmolenda) ChangesMachProcess has a MachTask as an ivar. In the MachProcess dtor, we call MachTask::Clear() to clear its state, before running the dtor of all our ivars, including the MachTask one. When we attach on darwin, MachProcess calls MachTask::StartExceptionThread which does the task_for_pid and then starts a thread to listen for mach messages. Then MachProcess calls ptrace(PT_ATTACHEXC). If that ptrace() fails, MachProcess will call MachTask::Clear. But the exception thread is now up & running and is not stopped; its ivars will be reset by the Clear() method, and its object will be freed after the dtor runs. Actually eliciting a crash in this scenario is very timing sensitive; I hand-modified debugserver to fail to PT_ATTACHEXC trying to simulate it on my desktop and was unable. But looking at the source, and an occasional crash report we've received, it's clear that this is possible. rdar://117521198 Full diff: https://github.com/llvm/llvm-project/pull/70979.diff 1 Files Affected:
diff --git a/lldb/tools/debugserver/source/MacOSX/MachTask.mm b/lldb/tools/debugserver/source/MacOSX/MachTask.mm
index 4f5b4039243f662..fd2ac64ac6cf79c 100644
--- a/lldb/tools/debugserver/source/MacOSX/MachTask.mm
+++ b/lldb/tools/debugserver/source/MacOSX/MachTask.mm
@@ -145,6 +145,8 @@
//----------------------------------------------------------------------
void MachTask::Clear() {
// Do any cleanup needed for this task
+ if (m_exception_thread)
+ ShutDownExcecptionThread();
m_task = TASK_NULL;
m_exception_thread = 0;
m_exception_port = MACH_PORT_NULL;
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JDevlieghere
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Nov 1, 2023
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…vm#70979) MachProcess has a MachTask as an ivar. In the MachProcess dtor, we call MachTask::Clear() to clear its state, before running the dtor of all our ivars, including the MachTask one. When we attach on darwin, MachProcess calls MachTask::StartExceptionThread which does the task_for_pid and then starts a thread to listen for mach messages. Then MachProcess calls ptrace(PT_ATTACHEXC). If that ptrace() fails, MachProcess will call MachTask::Clear. But the exception thread is now up & running and is not stopped; its ivars will be reset by the Clear() method, and its object will be freed after the dtor runs. Actually eliciting a crash in this scenario is very timing sensitive; I hand-modified debugserver to fail to PT_ATTACHEXC trying to simulate it on my desktop and was unable. But looking at the source, and an occasional crash report we've received, it's clear that this is possible. rdar://117521198 (cherry picked from commit 66b9283)
jasonmolenda
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…tion-thread-from-MachTask-Clear [lldb] [debugserver] Shut down the exception thread when clearing (llvm#70979)
jasonmolenda
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Nov 8, 2023
…vm#70979) MachProcess has a MachTask as an ivar. In the MachProcess dtor, we call MachTask::Clear() to clear its state, before running the dtor of all our ivars, including the MachTask one. When we attach on darwin, MachProcess calls MachTask::StartExceptionThread which does the task_for_pid and then starts a thread to listen for mach messages. Then MachProcess calls ptrace(PT_ATTACHEXC). If that ptrace() fails, MachProcess will call MachTask::Clear. But the exception thread is now up & running and is not stopped; its ivars will be reset by the Clear() method, and its object will be freed after the dtor runs. Actually eliciting a crash in this scenario is very timing sensitive; I hand-modified debugserver to fail to PT_ATTACHEXC trying to simulate it on my desktop and was unable. But looking at the source, and an occasional crash report we've received, it's clear that this is possible. rdar://117521198 (cherry picked from commit 66b9283)
jasonmolenda
added a commit
to swiftlang/llvm-project
that referenced
this pull request
Nov 8, 2023
…-when-clearing [lldb] [debugserver] Shut down the exception thread when clearing (llvm#70979)
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MachProcess has a MachTask as an ivar. In the MachProcess dtor, we call MachTask::Clear() to clear its state, before running the dtor of all our ivars, including the MachTask one.
When we attach on darwin, MachProcess calls MachTask::StartExceptionThread which does the task_for_pid and then starts a thread to listen for mach messages. Then MachProcess calls ptrace(PT_ATTACHEXC). If that ptrace() fails, MachProcess will call MachTask::Clear. But the exception thread is now up & running and is not stopped; its ivars will be reset by the Clear() method, and its object will be freed after the dtor runs.
Actually eliciting a crash in this scenario is very timing sensitive; I hand-modified debugserver to fail to PT_ATTACHEXC trying to simulate it on my desktop and was unable. But looking at the source, and an occasional crash report we've received, it's clear that this is possible.
rdar://117521198