Merge pull request #849 from DarkLordZach/xci

XCI and Encrypted NCA Support

6 files changed, 446 insertions, 44 deletions

diff --git a/src/core/file_sys/card_image.cpp b/src/core/file_sys/card_image.cpp
new file mode 100644
index 000000000..395eea8ae
--- /dev/null
+++ b/src/core/file_sys/card_image.cpp
@@ -0,0 +1,149 @@
+// Copyright 2018 yuzu emulator team
+// Licensed under GPLv2 or any later version
+// Refer to the license.txt file included.
+
+#include <array>
+#include <string>
+#include <core/loader/loader.h>
+#include "core/file_sys/card_image.h"
+#include "core/file_sys/partition_filesystem.h"
+#include "core/file_sys/vfs_offset.h"
+
+namespace FileSys {
+
+XCI::XCI(VirtualFile file_) : file(std::move(file_)), partitions(0x4) {
+    if (file->ReadObject(&header) != sizeof(GamecardHeader)) {
+        status = Loader::ResultStatus::ErrorInvalidFormat;
+        return;
+    }
+
+    if (header.magic != Common::MakeMagic('H', 'E', 'A', 'D')) {
+        status = Loader::ResultStatus::ErrorInvalidFormat;
+        return;
+    }
+
+    PartitionFilesystem main_hfs(
+        std::make_shared<OffsetVfsFile>(file, header.hfs_size, header.hfs_offset));
+
+    if (main_hfs.GetStatus() != Loader::ResultStatus::Success) {
+        status = main_hfs.GetStatus();
+        return;
+    }
+
+    static constexpr std::array<const char*, 0x4> partition_names = {"update", "normal", "secure",
+                                                                     "logo"};
+
+    for (XCIPartition partition :
+         {XCIPartition::Update, XCIPartition::Normal, XCIPartition::Secure, XCIPartition::Logo}) {
+        auto raw = main_hfs.GetFile(partition_names[static_cast<size_t>(partition)]);
+        if (raw != nullptr)
+            partitions[static_cast<size_t>(partition)] = std::make_shared<PartitionFilesystem>(raw);
+    }
+
+    auto result = AddNCAFromPartition(XCIPartition::Secure);
+    if (result != Loader::ResultStatus::Success) {
+        status = result;
+        return;
+    }
+
+    result = AddNCAFromPartition(XCIPartition::Update);
+    if (result != Loader::ResultStatus::Success) {
+        status = result;
+        return;
+    }
+
+    result = AddNCAFromPartition(XCIPartition::Normal);
+    if (result != Loader::ResultStatus::Success) {
+        status = result;
+        return;
+    }
+
+    if (GetFormatVersion() >= 0x2) {
+        result = AddNCAFromPartition(XCIPartition::Logo);
+        if (result != Loader::ResultStatus::Success) {
+            status = result;
+            return;
+        }
+    }
+
+    status = Loader::ResultStatus::Success;
+}
+
+Loader::ResultStatus XCI::GetStatus() const {
+    return status;
+}
+
+VirtualDir XCI::GetPartition(XCIPartition partition) const {
+    return partitions[static_cast<size_t>(partition)];
+}
+
+VirtualDir XCI::GetSecurePartition() const {
+    return GetPartition(XCIPartition::Secure);
+}
+
+VirtualDir XCI::GetNormalPartition() const {
+    return GetPartition(XCIPartition::Normal);
+}
+
+VirtualDir XCI::GetUpdatePartition() const {
+    return GetPartition(XCIPartition::Update);
+}
+
+VirtualDir XCI::GetLogoPartition() const {
+    return GetPartition(XCIPartition::Logo);
+}
+
+std::shared_ptr<NCA> XCI::GetNCAByType(NCAContentType type) const {
+    const auto iter =
+        std::find_if(ncas.begin(), ncas.end(),
+                     [type](const std::shared_ptr<NCA>& nca) { return nca->GetType() == type; });
+    return iter == ncas.end() ? nullptr : *iter;
+}
+
+VirtualFile XCI::GetNCAFileByType(NCAContentType type) const {
+    auto nca = GetNCAByType(type);
+    if (nca != nullptr)
+        return nca->GetBaseFile();
+    return nullptr;
+}
+
+std::vector<std::shared_ptr<VfsFile>> XCI::GetFiles() const {
+    return {};
+}
+
+std::vector<std::shared_ptr<VfsDirectory>> XCI::GetSubdirectories() const {
+    return std::vector<std::shared_ptr<VfsDirectory>>();
+}
+
+std::string XCI::GetName() const {
+    return file->GetName();
+}
+
+std::shared_ptr<VfsDirectory> XCI::GetParentDirectory() const {
+    return file->GetContainingDirectory();
+}
+
+bool XCI::ReplaceFileWithSubdirectory(VirtualFile file, VirtualDir dir) {
+    return false;
+}
+
+Loader::ResultStatus XCI::AddNCAFromPartition(XCIPartition part) {
+    if (partitions[static_cast<size_t>(part)] == nullptr) {
+        return Loader::ResultStatus::ErrorInvalidFormat;
+    }
+
+    for (const VirtualFile& file : partitions[static_cast<size_t>(part)]->GetFiles()) {
+        if (file->GetExtension() != "nca")
+            continue;
+        auto nca = std::make_shared<NCA>(file);
+        if (nca->GetStatus() == Loader::ResultStatus::Success)
+            ncas.push_back(std::move(nca));
+    }
+
+    return Loader::ResultStatus::Success;
+}
+
+u8 XCI::GetFormatVersion() const {
+    return GetLogoPartition() == nullptr ? 0x1 : 0x2;
+}
+} // namespace FileSys
diff --git a/src/core/file_sys/card_image.h b/src/core/file_sys/card_image.h
new file mode 100644
index 000000000..e089d737c
--- /dev/null
+++ b/src/core/file_sys/card_image.h
@@ -0,0 +1,96 @@
+// Copyright 2018 yuzu emulator team
+// Licensed under GPLv2 or any later version
+// Refer to the license.txt file included.
+
+#pragma once
+
+#include <array>
+#include <vector>
+#include "common/common_types.h"
+#include "common/swap.h"
+#include "core/file_sys/content_archive.h"
+#include "core/file_sys/vfs.h"
+#include "core/loader/loader.h"
+
+namespace FileSys {
+
+enum class GamecardSize : u8 {
+    S_1GB = 0xFA,
+    S_2GB = 0xF8,
+    S_4GB = 0xF0,
+    S_8GB = 0xE0,
+    S_16GB = 0xE1,
+    S_32GB = 0xE2,
+};
+
+struct GamecardInfo {
+    std::array<u8, 0x70> data;
+};
+static_assert(sizeof(GamecardInfo) == 0x70, "GamecardInfo has incorrect size.");
+
+struct GamecardHeader {
+    std::array<u8, 0x100> signature;
+    u32_le magic;
+    u32_le secure_area_start;
+    u32_le backup_area_start;
+    u8 kek_index;
+    GamecardSize size;
+    u8 header_version;
+    u8 flags;
+    u64_le package_id;
+    u64_le valid_data_end;
+    u128 info_iv;
+    u64_le hfs_offset;
+    u64_le hfs_size;
+    std::array<u8, 0x20> hfs_header_hash;
+    std::array<u8, 0x20> initial_data_hash;
+    u32_le secure_mode_flag;
+    u32_le title_key_flag;
+    u32_le key_flag;
+    u32_le normal_area_end;
+    GamecardInfo info;
+};
+static_assert(sizeof(GamecardHeader) == 0x200, "GamecardHeader has incorrect size.");
+
+enum class XCIPartition : u8 { Update, Normal, Secure, Logo };
+
+class XCI : public ReadOnlyVfsDirectory {
+public:
+    explicit XCI(VirtualFile file);
+
+    Loader::ResultStatus GetStatus() const;
+
+    u8 GetFormatVersion() const;
+
+    VirtualDir GetPartition(XCIPartition partition) const;
+    VirtualDir GetSecurePartition() const;
+    VirtualDir GetNormalPartition() const;
+    VirtualDir GetUpdatePartition() const;
+    VirtualDir GetLogoPartition() const;
+
+    std::shared_ptr<NCA> GetNCAByType(NCAContentType type) const;
+    VirtualFile GetNCAFileByType(NCAContentType type) const;
+
+    std::vector<std::shared_ptr<VfsFile>> GetFiles() const override;
+
+    std::vector<std::shared_ptr<VfsDirectory>> GetSubdirectories() const override;
+
+    std::string GetName() const override;
+
+    std::shared_ptr<VfsDirectory> GetParentDirectory() const override;
+
+protected:
+    bool ReplaceFileWithSubdirectory(VirtualFile file, VirtualDir dir) override;
+
+private:
+    Loader::ResultStatus AddNCAFromPartition(XCIPartition part);
+
+    VirtualFile file;
+    GamecardHeader header{};
+
+    Loader::ResultStatus status;
+
+    std::vector<VirtualDir> partitions;
+    std::vector<std::shared_ptr<NCA>> ncas;
+};
+} // namespace FileSys
diff --git a/src/core/file_sys/content_archive.cpp b/src/core/file_sys/content_archive.cpp
index 61cb0bbe3..79e70f6ef 100644
--- a/src/core/file_sys/content_archive.cpp
+++ b/src/core/file_sys/content_archive.cpp
@@ -4,12 +4,14 @@
 
 #include <algorithm>
 #include <utility>
-
+#include <boost/optional.hpp>
 #include "common/logging/log.h"
+#include "core/crypto/aes_util.h"
+#include "core/crypto/ctr_encryption_layer.h"
 #include "core/file_sys/content_archive.h"
+#include "core/file_sys/romfs.h"
 #include "core/file_sys/vfs_offset.h"
 #include "core/loader/loader.h"
-#include "romfs.h"
 
 namespace FileSys {
 
@@ -29,11 +31,19 @@ enum class NCASectionFilesystemType : u8 {
 struct NCASectionHeaderBlock {
     INSERT_PADDING_BYTES(3);
     NCASectionFilesystemType filesystem_type;
-    u8 crypto_type;
+    NCASectionCryptoType crypto_type;
     INSERT_PADDING_BYTES(3);
 };
 static_assert(sizeof(NCASectionHeaderBlock) == 0x8, "NCASectionHeaderBlock has incorrect size.");
 
+struct NCASectionRaw {
+    NCASectionHeaderBlock header;
+    std::array<u8, 0x138> block_data;
+    std::array<u8, 0x8> section_ctr;
+    INSERT_PADDING_BYTES(0xB8);
+};
+static_assert(sizeof(NCASectionRaw) == 0x200, "NCASectionRaw has incorrect size.");
+
 struct PFS0Superblock {
     NCASectionHeaderBlock header_block;
     std::array<u8, 0x20> hash;
@@ -43,67 +53,170 @@ struct PFS0Superblock {
     u64_le hash_table_size;
     u64_le pfs0_header_offset;
     u64_le pfs0_size;
-    INSERT_PADDING_BYTES(432);
+    INSERT_PADDING_BYTES(0x1B0);
 };
 static_assert(sizeof(PFS0Superblock) == 0x200, "PFS0Superblock has incorrect size.");
 
 struct RomFSSuperblock {
     NCASectionHeaderBlock header_block;
     IVFCHeader ivfc;
+    INSERT_PADDING_BYTES(0x118);
 };
-static_assert(sizeof(RomFSSuperblock) == 0xE8, "RomFSSuperblock has incorrect size.");
+static_assert(sizeof(RomFSSuperblock) == 0x200, "RomFSSuperblock has incorrect size.");
+
+union NCASectionHeader {
+    NCASectionRaw raw;
+    PFS0Superblock pfs0;
+    RomFSSuperblock romfs;
+};
+static_assert(sizeof(NCASectionHeader) == 0x200, "NCASectionHeader has incorrect size.");
+
+bool IsValidNCA(const NCAHeader& header) {
+    // TODO(DarkLordZach): Add NCA2/NCA0 support.
+    return header.magic == Common::MakeMagic('N', 'C', 'A', '3');
+}
+
+boost::optional<Core::Crypto::Key128> NCA::GetKeyAreaKey(NCASectionCryptoType type) const {
+    u8 master_key_id = header.crypto_type;
+    if (header.crypto_type_2 > master_key_id)
+        master_key_id = header.crypto_type_2;
+    if (master_key_id > 0)
+        --master_key_id;
+
+    if (!keys.HasKey(Core::Crypto::S128KeyType::KeyArea, master_key_id, header.key_index))
+        return boost::none;
+
+    std::vector<u8> key_area(header.key_area.begin(), header.key_area.end());
+    Core::Crypto::AESCipher<Core::Crypto::Key128> cipher(
+        keys.GetKey(Core::Crypto::S128KeyType::KeyArea, master_key_id, header.key_index),
+        Core::Crypto::Mode::ECB);
+    cipher.Transcode(key_area.data(), key_area.size(), key_area.data(), Core::Crypto::Op::Decrypt);
+
+    Core::Crypto::Key128 out;
+    if (type == NCASectionCryptoType::XTS)
+        std::copy(key_area.begin(), key_area.begin() + 0x10, out.begin());
+    else if (type == NCASectionCryptoType::CTR)
+        std::copy(key_area.begin() + 0x20, key_area.begin() + 0x30, out.begin());
+    else
+        LOG_CRITICAL(Crypto, "Called GetKeyAreaKey on invalid NCASectionCryptoType type={:02X}",
+                     static_cast<u8>(type));
+    u128 out_128{};
+    memcpy(out_128.data(), out.data(), 16);
+    LOG_DEBUG(Crypto, "called with crypto_rev={:02X}, kak_index={:02X}, key={:016X}{:016X}",
+              master_key_id, header.key_index, out_128[1], out_128[0]);
+
+    return out;
+}
+
+VirtualFile NCA::Decrypt(NCASectionHeader header, VirtualFile in, u64 starting_offset) const {
+    if (!encrypted)
+        return in;
+
+    switch (header.raw.header.crypto_type) {
+    case NCASectionCryptoType::NONE:
+        LOG_DEBUG(Crypto, "called with mode=NONE");
+        return in;
+    case NCASectionCryptoType::CTR:
+        LOG_DEBUG(Crypto, "called with mode=CTR, starting_offset={:016X}", starting_offset);
+        {
+            const auto key = GetKeyAreaKey(NCASectionCryptoType::CTR);
+            if (key == boost::none)
+                return nullptr;
+            auto out = std::make_shared<Core::Crypto::CTREncryptionLayer>(
+                std::move(in), key.value(), starting_offset);
+            std::vector<u8> iv(16);
+            for (u8 i = 0; i < 8; ++i)
+                iv[i] = header.raw.section_ctr[0x8 - i - 1];
+            out->SetIV(iv);
+            return std::static_pointer_cast<VfsFile>(out);
+        }
+    case NCASectionCryptoType::XTS:
+        // TODO(DarkLordZach): Implement XTSEncryptionLayer and title key encryption.
+    default:
+        LOG_ERROR(Crypto, "called with unhandled crypto type={:02X}",
+                  static_cast<u8>(header.raw.header.crypto_type));
+        return nullptr;
+    }
+}
 
 NCA::NCA(VirtualFile file_) : file(std::move(file_)) {
     if (sizeof(NCAHeader) != file->ReadObject(&header))
-        LOG_CRITICAL(Loader, "File reader errored out during header read.");
+        LOG_ERROR(Loader, "File reader errored out during header read.");
+
+    encrypted = false;
 
     if (!IsValidNCA(header)) {
-        status = Loader::ResultStatus::ErrorInvalidFormat;
-        return;
+        NCAHeader dec_header{};
+        Core::Crypto::AESCipher<Core::Crypto::Key256> cipher(
+            keys.GetKey(Core::Crypto::S256KeyType::Header), Core::Crypto::Mode::XTS);
+        cipher.XTSTranscode(&header, sizeof(NCAHeader), &dec_header, 0, 0x200,
+                            Core::Crypto::Op::Decrypt);
+        if (IsValidNCA(dec_header)) {
+            header = dec_header;
+            encrypted = true;
+        } else {
+            if (!keys.HasKey(Core::Crypto::S256KeyType::Header))
+                status = Loader::ResultStatus::ErrorMissingKeys;
+            else
+                status = Loader::ResultStatus::ErrorDecrypting;
+            return;
+        }
     }
 
-    std::ptrdiff_t number_sections =
+    const std::ptrdiff_t number_sections =
         std::count_if(std::begin(header.section_tables), std::end(header.section_tables),
                       [](NCASectionTableEntry entry) { return entry.media_offset > 0; });
 
+    std::vector<NCASectionHeader> sections(number_sections);
+    const auto length_sections = SECTION_HEADER_SIZE * number_sections;
+
+    if (encrypted) {
+        auto raw = file->ReadBytes(length_sections, SECTION_HEADER_OFFSET);
+        Core::Crypto::AESCipher<Core::Crypto::Key256> cipher(
+            keys.GetKey(Core::Crypto::S256KeyType::Header), Core::Crypto::Mode::XTS);
+        cipher.XTSTranscode(raw.data(), length_sections, sections.data(), 2, SECTION_HEADER_SIZE,
+                            Core::Crypto::Op::Decrypt);
+    } else {
+        file->ReadBytes(sections.data(), length_sections, SECTION_HEADER_OFFSET);
+    }
+
     for (std::ptrdiff_t i = 0; i < number_sections; ++i) {
-        // Seek to beginning of this section.
-        NCASectionHeaderBlock block{};
-        if (sizeof(NCASectionHeaderBlock) !=
-            file->ReadObject(&block, SECTION_HEADER_OFFSET + i * SECTION_HEADER_SIZE))
-            LOG_CRITICAL(Loader, "File reader errored out during header read.");
-
-        if (block.filesystem_type == NCASectionFilesystemType::ROMFS) {
-            RomFSSuperblock sb{};
-            if (sizeof(RomFSSuperblock) !=
-                file->ReadObject(&sb, SECTION_HEADER_OFFSET + i * SECTION_HEADER_SIZE))
-                LOG_CRITICAL(Loader, "File reader errored out during header read.");
+        auto section = sections[i];
 
+        if (section.raw.header.filesystem_type == NCASectionFilesystemType::ROMFS) {
             const size_t romfs_offset =
                 header.section_tables[i].media_offset * MEDIA_OFFSET_MULTIPLIER +
-                sb.ivfc.levels[IVFC_MAX_LEVEL - 1].offset;
-            const size_t romfs_size = sb.ivfc.levels[IVFC_MAX_LEVEL - 1].size;
-            files.emplace_back(std::make_shared<OffsetVfsFile>(file, romfs_size, romfs_offset));
-            romfs = files.back();
-        } else if (block.filesystem_type == NCASectionFilesystemType::PFS0) {
-            PFS0Superblock sb{};
-            // Seek back to beginning of this section.
-            if (sizeof(PFS0Superblock) !=
-                file->ReadObject(&sb, SECTION_HEADER_OFFSET + i * SECTION_HEADER_SIZE))
-                LOG_CRITICAL(Loader, "File reader errored out during header read.");
-
+                section.romfs.ivfc.levels[IVFC_MAX_LEVEL - 1].offset;
+            const size_t romfs_size = section.romfs.ivfc.levels[IVFC_MAX_LEVEL - 1].size;
+            auto dec =
+                Decrypt(section, std::make_shared<OffsetVfsFile>(file, romfs_size, romfs_offset),
+                        romfs_offset);
+            if (dec != nullptr) {
+                files.push_back(std::move(dec));
+                romfs = files.back();
+            } else {
+                status = Loader::ResultStatus::ErrorMissingKeys;
+                return;
+            }
+        } else if (section.raw.header.filesystem_type == NCASectionFilesystemType::PFS0) {
             u64 offset = (static_cast<u64>(header.section_tables[i].media_offset) *
                           MEDIA_OFFSET_MULTIPLIER) +
-                         sb.pfs0_header_offset;
+                         section.pfs0.pfs0_header_offset;
             u64 size = MEDIA_OFFSET_MULTIPLIER * (header.section_tables[i].media_end_offset -
                                                   header.section_tables[i].media_offset);
-            auto npfs = std::make_shared<PartitionFilesystem>(
-                std::make_shared<OffsetVfsFile>(file, size, offset));
+            auto dec =
+                Decrypt(section, std::make_shared<OffsetVfsFile>(file, size, offset), offset);
+            if (dec != nullptr) {
+                auto npfs = std::make_shared<PartitionFilesystem>(std::move(dec));
 
-            if (npfs->GetStatus() == Loader::ResultStatus::Success) {
-                dirs.emplace_back(npfs);
-                if (IsDirectoryExeFS(dirs.back()))
-                    exefs = dirs.back();
+                if (npfs->GetStatus() == Loader::ResultStatus::Success) {
+                    dirs.push_back(std::move(npfs));
+                    if (IsDirectoryExeFS(dirs.back()))
+                        exefs = dirs.back();
+                }
+            } else {
+                status = Loader::ResultStatus::ErrorMissingKeys;
+                return;
             }
         }
     }
@@ -153,6 +266,10 @@ VirtualDir NCA::GetExeFS() const {
     return exefs;
 }
 
+VirtualFile NCA::GetBaseFile() const {
+    return file;
+}
+
 bool NCA::ReplaceFileWithSubdirectory(VirtualFile file, VirtualDir dir) {
     return false;
 }
diff --git a/src/core/file_sys/content_archive.h b/src/core/file_sys/content_archive.h
index 0b8b9db61..6492163b5 100644
--- a/src/core/file_sys/content_archive.h
+++ b/src/core/file_sys/content_archive.h
@@ -8,14 +8,18 @@
 #include <memory>
 #include <string>
 #include <vector>
-
+#include <boost/optional.hpp>
 #include "common/common_funcs.h"
 #include "common/common_types.h"
 #include "common/swap.h"
+#include "core/crypto/key_manager.h"
 #include "core/file_sys/partition_filesystem.h"
+#include "core/loader/loader.h"
 
 namespace FileSys {
 
+union NCASectionHeader;
+
 enum class NCAContentType : u8 {
     Program = 0,
     Meta = 1,
@@ -24,6 +28,13 @@ enum class NCAContentType : u8 {
     Data = 4,
 };
 
+enum class NCASectionCryptoType : u8 {
+    NONE = 1,
+    XTS = 2,
+    CTR = 3,
+    BKTR = 4,
+};
+
 struct NCASectionTableEntry {
     u32_le media_offset;
     u32_le media_end_offset;
@@ -48,7 +59,7 @@ struct NCAHeader {
     std::array<u8, 0x10> rights_id;
     std::array<NCASectionTableEntry, 0x4> section_tables;
     std::array<std::array<u8, 0x20>, 0x4> hash_tables;
-    std::array<std::array<u8, 0x10>, 0x4> key_area;
+    std::array<u8, 0x40> key_area;
     INSERT_PADDING_BYTES(0xC0);
 };
 static_assert(sizeof(NCAHeader) == 0x400, "NCAHeader has incorrect size.");
@@ -58,10 +69,7 @@ inline bool IsDirectoryExeFS(const std::shared_ptr<VfsDirectory>& pfs) {
     return pfs->GetFile("main") != nullptr && pfs->GetFile("main.npdm") != nullptr;
 }
 
-inline bool IsValidNCA(const NCAHeader& header) {
-    return header.magic == Common::MakeMagic('N', 'C', 'A', '2') ||
-           header.magic == Common::MakeMagic('N', 'C', 'A', '3');
-}
+bool IsValidNCA(const NCAHeader& header);
 
 // An implementation of VfsDirectory that represents a Nintendo Content Archive (NCA) conatiner.
 // After construction, use GetStatus to determine if the file is valid and ready to be used.
@@ -81,10 +89,15 @@ public:
     VirtualFile GetRomFS() const;
     VirtualDir GetExeFS() const;
 
+    VirtualFile GetBaseFile() const;
+
 protected:
     bool ReplaceFileWithSubdirectory(VirtualFile file, VirtualDir dir) override;
 
 private:
+    boost::optional<Core::Crypto::Key128> GetKeyAreaKey(NCASectionCryptoType type) const;
+    VirtualFile Decrypt(NCASectionHeader header, VirtualFile in, u64 starting_offset) const;
+
     std::vector<VirtualDir> dirs;
     std::vector<VirtualFile> files;
 
@@ -95,6 +108,10 @@ private:
     NCAHeader header{};
 
     Loader::ResultStatus status{};
+
+    bool encrypted;
+
+    Core::Crypto::KeyManager keys;
 };
 
 } // namespace FileSys
diff --git a/src/core/file_sys/vfs.cpp b/src/core/file_sys/vfs.cpp
index 84a6a7397..dae1c16ef 100644
--- a/src/core/file_sys/vfs.cpp
+++ b/src/core/file_sys/vfs.cpp
@@ -285,6 +285,26 @@ bool ReadOnlyVfsDirectory::Rename(std::string_view name) {
     return false;
 }
 
+bool DeepEquals(const VirtualFile& file1, const VirtualFile& file2, size_t block_size) {
+    if (file1->GetSize() != file2->GetSize())
+        return false;
+
+    std::vector<u8> f1_v(block_size);
+    std::vector<u8> f2_v(block_size);
+    for (size_t i = 0; i < file1->GetSize(); i += block_size) {
+        auto f1_vs = file1->Read(f1_v.data(), block_size, i);
+        auto f2_vs = file2->Read(f2_v.data(), block_size, i);
+
+        if (f1_vs != f2_vs)
+            return false;
+        auto iters = std::mismatch(f1_v.begin(), f1_v.end(), f2_v.begin(), f2_v.end());
+        if (iters.first != f1_v.end() && iters.second != f2_v.end())
+            return false;
+    }
+
+    return true;
+}
+
 bool VfsRawCopy(VirtualFile src, VirtualFile dest) {
     if (src == nullptr || dest == nullptr)
         return false;
diff --git a/src/core/file_sys/vfs.h b/src/core/file_sys/vfs.h
index cf871edd6..fab9e2b45 100644
--- a/src/core/file_sys/vfs.h
+++ b/src/core/file_sys/vfs.h
@@ -245,6 +245,9 @@ struct ReadOnlyVfsDirectory : public VfsDirectory {
     bool Rename(std::string_view name) override;
 };
 
+// Compare the two files, byte-for-byte, in increments specificed by block_size
+bool DeepEquals(const VirtualFile& file1, const VirtualFile& file2, size_t block_size = 0x200);
+
 // A method that copies the raw data between two different implementations of VirtualFile. If you
 // are using the same implementation, it is probably better to use the Copy method in the parent
 // directory of src/dest.