From 716e0a126a22cfdeeaad6204f236324429345d2e Mon Sep 17 00:00:00 2001
From: Liam <byteslice@airmail.cc>
Date: Wed, 6 Sep 2023 01:06:03 -0400
Subject: core: implement basic integrity verification

---
 src/core/loader/nca.cpp | 76 +++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 76 insertions(+)

(limited to 'src/core/loader/nca.cpp')

diff --git a/src/core/loader/nca.cpp b/src/core/loader/nca.cpp
index 09d40e695..4feb6968a 100644
--- a/src/core/loader/nca.cpp
+++ b/src/core/loader/nca.cpp
@@ -3,6 +3,8 @@
 
 #include <utility>
 
+#include "common/hex_util.h"
+#include "common/scope_exit.h"
 #include "core/core.h"
 #include "core/file_sys/content_archive.h"
 #include "core/file_sys/nca_metadata.h"
@@ -12,6 +14,7 @@
 #include "core/hle/service/filesystem/filesystem.h"
 #include "core/loader/deconstructed_rom_directory.h"
 #include "core/loader/nca.h"
+#include "mbedtls/sha256.h"
 
 namespace Loader {
 
@@ -80,6 +83,79 @@ AppLoader_NCA::LoadResult AppLoader_NCA::Load(Kernel::KProcess& process, Core::S
     return load_result;
 }
 
+ResultStatus AppLoader_NCA::VerifyIntegrity(std::function<bool(size_t, size_t)> progress_callback) {
+    using namespace Common::Literals;
+
+    constexpr size_t NcaFileNameWithHashLength = 36;
+    constexpr size_t NcaFileNameHashLength = 32;
+    constexpr size_t NcaSha256HashLength = 32;
+    constexpr size_t NcaSha256HalfHashLength = NcaSha256HashLength / 2;
+
+    // Get the file name.
+    const auto name = file->GetName();
+
+    // We won't try to verify meta NCAs.
+    if (name.ends_with(".cnmt.nca")) {
+        return ResultStatus::Success;
+    }
+
+    // Check if we can verify this file. NCAs should be named after their hashes.
+    if (!name.ends_with(".nca") || name.size() != NcaFileNameWithHashLength) {
+        LOG_WARNING(Loader, "Unable to validate NCA with name {}", name);
+        return ResultStatus::ErrorIntegrityVerificationNotImplemented;
+    }
+
+    // Get the expected truncated hash of the NCA.
+    const auto input_hash =
+        Common::HexStringToVector(file->GetName().substr(0, NcaFileNameHashLength), false);
+
+    // Declare buffer to read into.
+    std::vector<u8> buffer(4_MiB);
+
+    // Initialize sha256 verification context.
+    mbedtls_sha256_context ctx;
+    mbedtls_sha256_init(&ctx);
+    mbedtls_sha256_starts_ret(&ctx, 0);
+
+    // Ensure we maintain a clean state on exit.
+    SCOPE_EXIT({ mbedtls_sha256_free(&ctx); });
+
+    // Declare counters.
+    const size_t total_size = file->GetSize();
+    size_t processed_size = 0;
+
+    // Begin iterating the file.
+    while (processed_size < total_size) {
+        // Refill the buffer.
+        const size_t intended_read_size = std::min(buffer.size(), total_size - processed_size);
+        const size_t read_size = file->Read(buffer.data(), intended_read_size, processed_size);
+
+        // Update the hash function with the buffer contents.
+        mbedtls_sha256_update_ret(&ctx, buffer.data(), read_size);
+
+        // Update counters.
+        processed_size += read_size;
+
+        // Call the progress function.
+        if (!progress_callback(processed_size, total_size)) {
+            return ResultStatus::ErrorIntegrityVerificationFailed;
+        }
+    }
+
+    // Finalize context and compute the output hash.
+    std::array<u8, NcaSha256HashLength> output_hash;
+    mbedtls_sha256_finish_ret(&ctx, output_hash.data());
+
+    // Compare to expected.
+    if (std::memcmp(input_hash.data(), output_hash.data(), NcaSha256HalfHashLength) != 0) {
+        LOG_ERROR(Loader, "NCA hash mismatch detected for file {}", name);
+        return ResultStatus::ErrorIntegrityVerificationFailed;
+    }
+
+    // File verified.
+    return ResultStatus::Success;
+}
+
 ResultStatus AppLoader_NCA::ReadRomFS(FileSys::VirtualFile& dir) {
     if (nca == nullptr) {
         return ResultStatus::ErrorNotInitialized;
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