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Kernel: Add 'ptrace' syscall

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This commit adds a basic implementation of
the ptrace syscall, which allows one process
(the tracer) to control another process (the tracee).

While a process is being traced, it is stopped whenever a signal is
received (other than SIGCONT).

The tracer can start tracing another thread with PT_ATTACH,
which causes the tracee to stop.

From there, the tracer can use PT_CONTINUE
to continue the execution of the tracee,
or use other request codes (which haven't been implemented yet)
to modify the state of the tracee.

Additional request codes are PT_SYSCALL, which causes the tracee to
continue exection but stop at the next entry or exit from a syscall,
and PT_GETREGS which fethces the last saved register set of the tracee
(can be used to inspect syscall arguments and return value).

A special request code is PT_TRACE_ME, which is issued by the tracee
and causes it to stop when it calls execve and wait for the
tracer to attach.
This commit is contained in:
Itamar 2020-03-28 11:47:16 +03:00 • committed by Andreas Kling
parent c9396be83f
commit 6b74d38aab
13 changed files with 300 additions and 102 deletions
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41
Kernel/Thread.cpp
View file

@ -33,6 +33,7 @@
#include <Kernel/Profiling.h>
#include <Kernel/Scheduler.h>
#include <Kernel/Thread.h>
#include <Kernel/ThreadTracer.h>
#include <Kernel/VM/MemoryManager.h>
#include <Kernel/VM/PageDirectory.h>
#include <Kernel/VM/ProcessPagingScope.h>
@ -508,6 +509,29 @@ ShouldUnblockThread Thread::dispatch_signal(u8 signal)
ASSERT(m_stop_state != State::Invalid);
set_state(m_stop_state);
m_stop_state = State::Invalid;
// make sure SemiPermanentBlocker is unblocked
if (m_state != Thread::Runnable && m_state != Thread::Running
&& m_blocker && m_blocker->is_reason_signal())
unblock();
}
else {
auto* thread_tracer = tracer();
if (thread_tracer != nullptr) {
// when a thread is traced, it should be stopped whenever it receives a signal
// the tracer is notified of this by using waitpid()
// only "pending signals" from the tracer are sent to the tracee
if (!thread_tracer->has_pending_signal(signal)) {
m_stop_signal = signal;
// make sure SemiPermanentBlocker is unblocked
if (m_blocker && m_blocker->is_reason_signal())
unblock();
m_stop_state = m_state;
set_state(Stopped);
return ShouldUnblockThread::No;
}
thread_tracer->unset_signal(signal);
}
}
auto handler_vaddr = action.handler_or_sigaction;
@ -900,4 +924,21 @@ void Thread::reset_fpu_state()
memcpy(m_fpu_state, &s_clean_fpu_state, sizeof(FPUState));
}
void Thread::start_tracing_from(pid_t tracer)
{
m_tracer = ThreadTracer::create(tracer);
}
void Thread::stop_tracing()
{
m_tracer = nullptr;
}
void Thread::tracer_trap(const RegisterState& regs)
{
ASSERT(m_tracer.ptr());
m_tracer->set_regs(regs);
send_urgent_signal_to_self(SIGTRAP);
}
}