[core/loader] Implement a bit improper ASLR (#2945)

A bit improper of an ASLR - it does something but something good? Who knows...
All I know is that there is a non-uniform distrobution for rand() and that rng_seed is likely a better solution?
I don't know

Signed-off-by: lizzie lizzie@eden-emu.dev

Reviewed-on: https://git.eden-emu.dev/eden-emu/eden/pulls/2945
Reviewed-by: Maufeat <sahyno1996@gmail.com>
Reviewed-by: MaranBr <maranbr@eden-emu.dev>
Co-authored-by: lizzie <lizzie@eden-emu.dev>
Co-committed-by: lizzie <lizzie@eden-emu.dev>

src/core/hle/kernel/k_process.cpp

@@ -28,9 +28,6 @@ namespace Kernel {
 
 namespace {
 
-// TODO: Remove this workaround when proper ASLR is implemented for all address spaces.
-constexpr u64 CodeStartOffset = 0x500000UL;
-
 Result TerminateChildren(KernelCore& kernel, KProcess* process,
                          const KThread* thread_to_not_terminate) {
     // Request that all children threads terminate.
@@ -1157,7 +1154,7 @@ KProcess::KProcess(KernelCore& kernel)
 KProcess::~KProcess() = default;
 
 Result KProcess::LoadFromMetadata(const FileSys::ProgramMetadata& metadata, std::size_t code_size,
-                                  KProcessAddress aslr_space_start, bool is_hbl) {
+    KProcessAddress aslr_space_start, size_t aslr_space_offset, bool is_hbl) {
     // Create a resource limit for the process.
     const auto pool = static_cast<KMemoryManager::Pool>(metadata.GetPoolPartition());
     const auto physical_memory_size = m_kernel.MemoryManager().GetSize(pool);
@@ -1187,25 +1184,24 @@ Result KProcess::LoadFromMetadata(const FileSys::ProgramMetadata& metadata, std:
     // Set the address space type and code address.
     switch (metadata.GetAddressSpaceType()) {
     case FileSys::ProgramAddressSpaceType::Is39Bit:
-        flag |= Svc::CreateProcessFlag::AddressSpace64Bit;
-
         // For 39-bit processes, the ASLR region starts at 0x800'0000 and is ~512GiB large.
         // However, some (buggy) programs/libraries like skyline incorrectly depend on the
         // existence of ASLR pages before the entry point, so we will adjust the load address
         // to point to about 2GiB into the ASLR region.
-        code_address = 0x8000'0000;
+        flag |= Svc::CreateProcessFlag::AddressSpace64Bit;
+        code_address = 0x8000'0000 + aslr_space_offset;
         break;
     case FileSys::ProgramAddressSpaceType::Is36Bit:
         flag |= Svc::CreateProcessFlag::AddressSpace64BitDeprecated;
-        code_address = 0x800'0000;
+        code_address = 0x800'0000 + aslr_space_offset;
         break;
     case FileSys::ProgramAddressSpaceType::Is32Bit:
         flag |= Svc::CreateProcessFlag::AddressSpace32Bit;
-        code_address = 0x20'0000 + CodeStartOffset;
+        code_address = 0x20'0000 + aslr_space_offset;
         break;
     case FileSys::ProgramAddressSpaceType::Is32BitNoMap:
         flag |= Svc::CreateProcessFlag::AddressSpace32BitWithoutAlias;
-        code_address = 0x20'0000 + CodeStartOffset;
+        code_address = 0x20'0000 + aslr_space_offset;
         break;
     }
 

src/core/hle/kernel/k_process.h

@@ -511,7 +511,7 @@ public:
 
 public:
     Result LoadFromMetadata(const FileSys::ProgramMetadata& metadata, std::size_t code_size,
-                            KProcessAddress aslr_space_start, bool is_hbl);
+        KProcessAddress aslr_space_start, size_t aslr_space_offset, bool is_hbl);
 
     void LoadModule(CodeSet code_set, KProcessAddress base_addr);
 

src/core/loader/deconstructed_rom_directory.cpp

@@ -1,3 +1,6 @@
+// SPDX-FileCopyrightText: Copyright 2025 Eden Emulator Project
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 // SPDX-FileCopyrightText: Copyright 2018 yuzu Emulator Project
 // SPDX-License-Identifier: GPL-2.0-or-later
 
@@ -223,8 +226,13 @@ AppLoader_DeconstructedRomDirectory::LoadResult AppLoader_DeconstructedRomDirect
     // Add patch size to the total module size
     code_size += patch_ctx.GetTotalPatchSize();
 
+    // TODO: this is bad form of ASLR, it sucks
+    size_t aslr_offset = ((::Settings::values.rng_seed_enabled.GetValue()
+        ? ::Settings::values.rng_seed.GetValue()
+        : std::rand()) * 0x734287f27) & 0xfff000;
+
     // Setup the process code layout
-    if (process.LoadFromMetadata(metadata, code_size, fastmem_base, is_hbl).IsError()) {
+    if (process.LoadFromMetadata(metadata, code_size, fastmem_base, aslr_offset, is_hbl).IsError()) {
         return {ResultStatus::ErrorUnableToParseKernelMetadata, {}};
     }
 

src/core/loader/kip.cpp

@@ -5,6 +5,7 @@
 // SPDX-License-Identifier: GPL-2.0-or-later
 
 #include <cstring>
+#include "common/settings.h"
 #include "core/file_sys/kernel_executable.h"
 #include "core/file_sys/program_metadata.h"
 #include "core/hle/kernel/code_set.h"
@@ -76,11 +77,10 @@ AppLoader::LoadResult AppLoader_KIP::Load(Kernel::KProcess& process,
     Kernel::CodeSet codeset;
     Kernel::PhysicalMemory program_image;
 
-    const auto load_segment = [&program_image](Kernel::CodeSet::Segment& segment,
+    const auto load_segment = [&program_image](Kernel::CodeSet::Segment& segment, const std::vector<u8>& data, u32 offset) {
-                                               const std::vector<u8>& data, u32 offset) {
         segment.addr = offset;
         segment.offset = offset;
-        segment.size = PageAlignSize(static_cast<u32>(data.size()));
+        segment.size = PageAlignSize(u32(data.size()));
         program_image.resize(offset + data.size());
         std::memcpy(program_image.data() + offset, data.data(), data.size());
     };
@@ -92,10 +92,14 @@ AppLoader::LoadResult AppLoader_KIP::Load(Kernel::KProcess& process,
     program_image.resize(PageAlignSize(kip->GetBSSOffset()) + kip->GetBSSSize());
     codeset.DataSegment().size += kip->GetBSSSize();
 
+    // TODO: this is bad form of ASLR, it sucks
+    size_t aslr_offset = ((::Settings::values.rng_seed_enabled.GetValue()
+        ? ::Settings::values.rng_seed.GetValue()
+        : std::rand()) * 0x734287f27) & 0xfff000;
+
     // Setup the process code layout
     if (process
-            .LoadFromMetadata(FileSys::ProgramMetadata::GetDefault(), program_image.size(), 0,
+            .LoadFromMetadata(FileSys::ProgramMetadata::GetDefault(), program_image.size(), 0, aslr_offset, false)
-                              false)
             .IsError()) {
         return {ResultStatus::ErrorNotInitialized, {}};
     }

src/core/loader/nro.cpp

@@ -1,3 +1,6 @@
+// SPDX-FileCopyrightText: Copyright 2025 Eden Emulator Project
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 // SPDX-FileCopyrightText: Copyright 2018 yuzu Emulator Project
 // SPDX-License-Identifier: GPL-2.0-or-later
 
@@ -237,10 +240,14 @@ static bool LoadNroImpl(Core::System& system, Kernel::KProcess& process,
         return 0;
     }();
 
+    // TODO: this is bad form of ASLR, it sucks
+    size_t aslr_offset = ((::Settings::values.rng_seed_enabled.GetValue()
+        ? ::Settings::values.rng_seed.GetValue()
+        : std::rand()) * 0x734287f27) & 0xfff000;
+
     // Setup the process code layout
     if (process
-            .LoadFromMetadata(FileSys::ProgramMetadata::GetDefault(), image_size, fastmem_base,
+            .LoadFromMetadata(FileSys::ProgramMetadata::GetDefault(), image_size, fastmem_base, aslr_offset, false)
-                              false)
             .IsError()) {
         return false;
     }