UserspaceEmulator: Make mmap'ed memory track read/write protection

Here's the first time we get a taste of better information than the
real hardware can give us: unlike x86 CPUs, we can actually support
write-only memory, so now we do!

While this isn't immediately useful, it's still pretty cool. :^)

DevTools/UserspaceEmulator/CMakeLists.txt

@@ -1,5 +1,6 @@
 set(SOURCES
     Emulator.cpp
+    MmapRegion.cpp
     SimpleRegion.cpp
     SoftCPU.cpp
     SoftMMU.cpp

DevTools/UserspaceEmulator/Emulator.cpp

@@ -25,6 +25,7 @@
  */
 
 #include "Emulator.h"
+#include "MmapRegion.h"
 #include "SimpleRegion.h"
 #include "SoftCPU.h"
 #include <AK/LexicalPath.h>
@@ -44,10 +45,20 @@ namespace UserspaceEmulator {
 static constexpr u32 stack_location = 0x10000000;
 static constexpr size_t stack_size = 64 * KB;
 
+static Emulator* s_the;
+
+Emulator& Emulator::the()
+{
+    ASSERT(s_the);
+    return *s_the;
+}
+
 Emulator::Emulator(const Vector<String>& arguments, NonnullRefPtr<ELF::Loader> elf)
     : m_elf(move(elf))
     , m_cpu(*this)
 {
+    ASSERT(!s_the);
+    s_the = this;
     setup_stack(arguments);
 }
 
@@ -315,7 +326,7 @@ u32 Emulator::virt$mmap(u32 params_addr)
 
     next_address = final_address + final_size;
 
-    mmu().add_region(make<SimpleRegion>(final_address, final_size));
+    mmu().add_region(make<MmapRegion>(final_address, final_size, params.prot));
 
     return final_address;
 }

DevTools/UserspaceEmulator/Emulator.h

@@ -37,6 +37,8 @@ namespace UserspaceEmulator {
 
 class Emulator {
 public:
+    static Emulator& the();
+
     Emulator(const Vector<String>& arguments, NonnullRefPtr<ELF::Loader>);
 
     bool load_elf();

DevTools/UserspaceEmulator/MmapRegion.cpp

@@ -0,0 +1,117 @@
+/*
+ * Copyright (c) 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 "MmapRegion.h"
+#include "Emulator.h"
+#include <sys/mman.h>
+
+namespace UserspaceEmulator {
+
+MmapRegion::MmapRegion(u32 base, u32 size, int prot)
+    : Region(base, size)
+    , m_prot(prot)
+{
+    m_data = (u8*)calloc(1, size);
+}
+
+MmapRegion::~MmapRegion()
+{
+    free(m_data);
+}
+
+u8 MmapRegion::read8(FlatPtr offset)
+{
+    if (!is_readable()) {
+        warn() << "8-bit read from unreadable MmapRegion @ " << (const void*)(base() + offset);
+        Emulator::the().dump_backtrace();
+        TODO();
+    }
+
+    ASSERT(offset < size());
+    return *reinterpret_cast<const u8*>(m_data + offset);
+}
+
+u16 MmapRegion::read16(u32 offset)
+{
+    if (!is_readable()) {
+        warn() << "16-bit from unreadable MmapRegion @ " << (const void*)(base() + offset);
+        Emulator::the().dump_backtrace();
+        TODO();
+    }
+
+    ASSERT(offset + 1 < size());
+    return *reinterpret_cast<const u16*>(m_data + offset);
+}
+
+u32 MmapRegion::read32(u32 offset)
+{
+    if (!is_readable()) {
+        warn() << "32-bit read from unreadable MmapRegion @ " << (const void*)(base() + offset);
+        Emulator::the().dump_backtrace();
+        TODO();
+    }
+
+    ASSERT(offset + 3 < size());
+    return *reinterpret_cast<const u32*>(m_data + offset);
+}
+
+void MmapRegion::write8(u32 offset, u8 value)
+{
+    if (!is_writable()) {
+        warn() << "8-bit write to unreadable MmapRegion @ " << (const void*)(base() + offset);
+        Emulator::the().dump_backtrace();
+        TODO();
+    }
+
+    ASSERT(offset < size());
+    *reinterpret_cast<u8*>(m_data + offset) = value;
+}
+
+void MmapRegion::write16(u32 offset, u16 value)
+{
+    if (!is_writable()) {
+        warn() << "16-bit write to unreadable MmapRegion @ " << (const void*)(base() + offset);
+        Emulator::the().dump_backtrace();
+        TODO();
+    }
+
+    ASSERT(offset + 1 < size());
+    *reinterpret_cast<u16*>(m_data + offset) = value;
+}
+
+void MmapRegion::write32(u32 offset, u32 value)
+{
+    if (!is_writable()) {
+        warn() << "32-bit write to unreadable MmapRegion @ " << (const void*)(base() + offset);
+        Emulator::the().dump_backtrace();
+        TODO();
+    }
+
+    ASSERT(offset + 3 < size());
+    *reinterpret_cast<u32*>(m_data + offset) = value;
+}
+
+}

DevTools/UserspaceEmulator/MmapRegion.h

@@ -0,0 +1,58 @@
+/*
+ * Copyright (c) 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.
+ */
+
+#pragma once
+
+#include "SoftMMU.h"
+#include <sys/mman.h>
+
+namespace UserspaceEmulator {
+
+class MmapRegion final : public SoftMMU::Region {
+public:
+    MmapRegion(u32 base, u32 size, int prot);
+    virtual ~MmapRegion() override;
+
+    virtual u8 read8(u32 offset) override;
+    virtual u16 read16(u32 offset) override;
+    virtual u32 read32(u32 offset) override;
+
+    virtual void write8(u32 offset, u8 value) override;
+    virtual void write16(u32 offset, u16 value) override;
+    virtual void write32(u32 offset, u32 value) override;
+
+    u8* data() { return m_data; }
+
+    bool is_readable() const { return m_prot & PROT_READ; }
+    bool is_writable() const { return m_prot & PROT_WRITE; }
+    bool is_executable() const { return m_prot & PROT_EXEC; }
+
+private:
+    u8* m_data { nullptr };
+    int m_prot { 0 };
+};
+
+}