Kernel: Move syscall implementations out of Process.cpp

This is something I've been meaning to do for a long time, and here we
finally go. This patch moves all sys$foo functions out of Process.cpp
and into files in Kernel/Syscalls/.

It's not exactly one syscall per file (although it could be, but I got
a bit tired of the repetitive work here..)

This makes hacking on individual syscalls a lot less painful since you
don't have to rebuild nearly as much code every time. I'm also hopeful
that this makes it easier to understand individual syscalls. :^)

Kernel/Syscalls/ptrace.cpp

@@ -0,0 +1,112 @@
+/*
+ * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <Kernel/Process.h>
+#include <Kernel/Ptrace.h>
+#include <Kernel/VM/MemoryManager.h>
+#include <Kernel/VM/PrivateInodeVMObject.h>
+#include <Kernel/VM/ProcessPagingScope.h>
+#include <Kernel/VM/Region.h>
+#include <Kernel/VM/SharedInodeVMObject.h>
+
+namespace Kernel {
+
+int Process::sys$ptrace(const Syscall::SC_ptrace_params* user_params)
+{
+    REQUIRE_PROMISE(proc);
+    Syscall::SC_ptrace_params params;
+    if (!validate_read_and_copy_typed(&params, user_params))
+        return -EFAULT;
+    auto result = Ptrace::handle_syscall(params, *this);
+    return result.is_error() ? result.error() : result.value();
+}
+
+bool Process::has_tracee_thread(int tracer_pid) const
+{
+    bool has_tracee = false;
+
+    for_each_thread([&](Thread& t) {
+        if (t.tracer() && t.tracer()->tracer_pid() == tracer_pid) {
+            has_tracee = true;
+            return IterationDecision::Break;
+        }
+        return IterationDecision::Continue;
+    });
+    return has_tracee;
+}
+
+KResultOr<u32> Process::peek_user_data(u32* address)
+{
+    if (!MM.validate_user_read(*this, VirtualAddress(address), sizeof(u32))) {
+        dbg() << "Invalid address for peek_user_data: " << address;
+        return KResult(-EFAULT);
+    }
+    uint32_t result;
+
+    // This function can be called from the context of another
+    // process that called PT_PEEK
+    ProcessPagingScope scope(*this);
+    copy_from_user(&result, address);
+
+    return result;
+}
+
+KResult Process::poke_user_data(u32* address, u32 data)
+{
+    // We validate for read (rather than write) because PT_POKE can write to readonly pages.
+    // So we effectively only care that the poke operation is trying to write to user pages.
+    if (!MM.validate_user_read(*this, VirtualAddress(address), sizeof(u32))) {
+        dbg() << "Invalid address for poke_user_data: " << address;
+        return KResult(-EFAULT);
+    }
+    ProcessPagingScope scope(*this);
+    Range range = { VirtualAddress(address), sizeof(u32) };
+    auto* region = region_containing(range);
+    ASSERT(region != nullptr);
+    if (region->is_shared()) {
+        // If the region is shared, we change its vmobject to a PrivateInodeVMObject
+        // to prevent the write operation from chaning any shared inode data
+        ASSERT(region->vmobject().is_shared_inode());
+        region->set_vmobject(PrivateInodeVMObject::create_with_inode(static_cast<SharedInodeVMObject&>(region->vmobject()).inode()));
+        region->set_shared(false);
+    }
+    const bool was_writable = region->is_writable();
+    if (!was_writable) //TODO refactor into scopeguard
+    {
+        region->set_writable(true);
+        region->remap();
+    }
+
+    copy_to_user(address, &data);
+
+    if (!was_writable) {
+        region->set_writable(false);
+        region->remap();
+    }
+    return KResult(KSuccess);
+}
+
+}