diff --git a/libraries/libstratosphere/source/os/impl/os_address_space_allocator.cpp b/libraries/libstratosphere/source/os/impl/os_address_space_allocator.cpp
new file mode 100644
index 000000000..7209bc96b
--- /dev/null
+++ b/libraries/libstratosphere/source/os/impl/os_address_space_allocator.cpp
@@ -0,0 +1,86 @@
+/*
+ * Copyright (c) 2018-2020 Atmosphère-NX
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms and conditions of the GNU General Public License,
+ * version 2, as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+#include <stratosphere.hpp>
+#include "os_address_space_allocator_types.hpp"
+#include "os_rng_manager.hpp"
+
+namespace ams::os::impl {
+
+    AddressSpaceAllocator::AddressSpaceAllocator(uintptr_t sa, uintptr_t ea, size_t gsz) : cs() {
+        /* Check preconditions. */
+        AMS_ASSERT(sa >= gsz);
+        AMS_ASSERT(ea + gsz >= ea);
+
+        this->guard_page_count = util::DivideUp(gsz, MemoryPageSize);
+        this->start_page       = sa / MemoryPageSize;
+        this->end_page         = (ea / MemoryPageSize) + this->guard_page_count;
+    }
+
+    bool AddressSpaceAllocator::GetNextNonOverlappedNodeUnsafe(uintptr_t page, size_t page_num) {
+        AMS_ASSERT(page < (page + page_num));
+
+        return CheckFreeSpace(page * MemoryPageSize, page_num * MemoryPageSize);
+    }
+
+    void *AddressSpaceAllocator::AllocateSpace(size_t size, size_t align) {
+        /* Check pre-conditions. */
+        AMS_ASSERT(align > 0);
+
+        /* Determine the page count. */
+        const size_t page_count = util::DivideUp(size, MemoryPageSize);
+
+        /* Determine the alignment pages. */
+        AMS_ASSERT(util::IsAligned(align, MemoryPageSize));
+        const size_t align_page_count = align / MemoryPageSize;
+
+        /* Check the page count. */
+        if (page_count > this->end_page - this->guard_page_count) {
+            return nullptr;
+        }
+
+        /* Determine the range to look in. */
+        const uintptr_t rand_start = util::DivideUp(this->start_page + this->guard_page_count, align_page_count);
+        const uintptr_t rand_end   = (this->end_page - page_count - this->guard_page_count) / align_page_count;
+
+        /* Check that we can find a space. */
+        if (rand_start > rand_end) {
+            return nullptr;
+        }
+
+        /* Try to find space up to 512 times. */
+        for (size_t i = 0; i < 512; ++i) {
+            /* Acquire exclusive access before doing calculations. */
+            std::scoped_lock lk(this->cs);
+
+            /* Determine a random page. */
+            const uintptr_t target = ((GetRngManager().GenerateRandomU64() % (rand_end - rand_start + 1)) + rand_start) * align_page_count;
+            AMS_ASSERT(this->start_page <= target - this->guard_page_count && target + page_count + this->guard_page_count <= this->end_page);
+
+            /* If the page is valid, use it. */
+            if (GetNextNonOverlappedNodeUnsafe(target - this->guard_page_count, page_count + 2 * this->guard_page_count)) {
+                return reinterpret_cast<void *>(target * MemoryPageSize);
+            }
+        }
+
+        /* We failed to find space. */
+        return nullptr;
+    }
+
+    bool AddressSpaceAllocator::CheckGuardSpace(uintptr_t address, size_t size, size_t guard_size) {
+        return CheckFreeSpace(address - guard_size, guard_size) && CheckFreeSpace(address + size, guard_size);
+    }
+
+}
diff --git a/libraries/libstratosphere/source/os/impl/os_address_space_allocator_impl.os.horizon.hpp b/libraries/libstratosphere/source/os/impl/os_address_space_allocator_impl.os.horizon.hpp
new file mode 100644
index 000000000..925fc17fe
--- /dev/null
+++ b/libraries/libstratosphere/source/os/impl/os_address_space_allocator_impl.os.horizon.hpp
@@ -0,0 +1,31 @@
+/*
+ * Copyright (c) 2018-2020 Atmosphère-NX
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms and conditions of the GNU General Public License,
+ * version 2, as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+#pragma once
+#include <stratosphere.hpp>
+
+namespace ams::os::impl {
+
+    inline bool CheckFreeSpace(uintptr_t address, size_t size) {
+        /* Query the memory. */
+        svc::MemoryInfo memory_info;
+        svc::PageInfo page_info;
+        const auto result = svc::QueryMemory(std::addressof(memory_info), std::addressof(page_info), address);
+        AMS_ASSERT(R_SUCCEEDED(result));
+
+        return memory_info.state == svc::MemoryState_Free && address + size <= memory_info.addr + memory_info.size;
+    }
+
+}
diff --git a/libraries/libstratosphere/source/os/impl/os_address_space_allocator_types.hpp b/libraries/libstratosphere/source/os/impl/os_address_space_allocator_types.hpp
new file mode 100644
index 000000000..ff602b115
--- /dev/null
+++ b/libraries/libstratosphere/source/os/impl/os_address_space_allocator_types.hpp
@@ -0,0 +1,44 @@
+/*
+ * Copyright (c) 2018-2020 Atmosphère-NX
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms and conditions of the GNU General Public License,
+ * version 2, as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+#pragma once
+#include <stratosphere.hpp>
+
+#ifdef ATMOSPHERE_OS_HORIZON
+    #include "os_address_space_allocator_impl.os.horizon.hpp"
+#else
+    #error "Unknown OS for AddressSpaceAllocatorImpl"
+#endif
+
+namespace ams::os::impl {
+
+    class AddressSpaceAllocator {
+        NON_COPYABLE(AddressSpaceAllocator);
+        NON_MOVEABLE(AddressSpaceAllocator);
+        private:
+            InternalCriticalSection cs;
+            uintptr_t start_page;
+            uintptr_t end_page;
+            size_t guard_page_count;
+        private:
+            bool GetNextNonOverlappedNodeUnsafe(uintptr_t page, size_t page_num);
+        public:
+            AddressSpaceAllocator(uintptr_t sa, uintptr_t ea, size_t gsz);
+
+            void *AllocateSpace(size_t size, size_t align);
+            bool CheckGuardSpace(uintptr_t address, size_t size, size_t guard_size);
+    };
+
+}
diff --git a/libraries/libstratosphere/source/os/impl/os_aslr_space_manager.hpp b/libraries/libstratosphere/source/os/impl/os_aslr_space_manager.hpp
new file mode 100644
index 000000000..224b0107f
--- /dev/null
+++ b/libraries/libstratosphere/source/os/impl/os_aslr_space_manager.hpp
@@ -0,0 +1,27 @@
+/*
+ * Copyright (c) 2018-2020 Atmosphère-NX
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms and conditions of the GNU General Public License,
+ * version 2, as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+#pragma once
+#include <stratosphere.hpp>
+#include "os_aslr_space_manager_types.hpp"
+#include "os_resource_manager.hpp"
+
+namespace ams::os::impl {
+
+    ALWAYS_INLINE AslrSpaceManager &GetAslrSpaceManager() {
+        return GetResourceManager().GetAslrSpaceManager();
+    }
+
+}
diff --git a/libraries/libstratosphere/source/os/impl/os_aslr_space_manager_impl.os.horizon.hpp b/libraries/libstratosphere/source/os/impl/os_aslr_space_manager_impl.os.horizon.hpp
new file mode 100644
index 000000000..ca1a7a4cd
--- /dev/null
+++ b/libraries/libstratosphere/source/os/impl/os_aslr_space_manager_impl.os.horizon.hpp
@@ -0,0 +1,85 @@
+/*
+ * Copyright (c) 2018-2020 Atmosphère-NX
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms and conditions of the GNU General Public License,
+ * version 2, as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+#pragma once
+#include <stratosphere.hpp>
+
+namespace ams::os::impl {
+
+    class AslrSpaceManagerHorizonImpl {
+        NON_COPYABLE(AslrSpaceManagerHorizonImpl);
+        NON_MOVEABLE(AslrSpaceManagerHorizonImpl);
+        private:
+            static constexpr u64 AslrBase32Bit           = 0x0000200000ul;
+            static constexpr u64 AslrSize32Bit           = 0x003FE00000ul;
+            static constexpr u64 AslrBase64BitDeprecated = 0x0008000000ul;
+            static constexpr u64 AslrSize64BitDeprecated = 0x0078000000ul;
+            static constexpr u64 AslrBase64Bit           = 0x0008000000ul;
+            static constexpr u64 AslrSize64Bit           = 0x7FF8000000ul;
+        private:
+            static u64 GetAslrInfo(svc::InfoType type) {
+                u64 value;
+                R_ABORT_UNLESS(svc::GetInfo(std::addressof(value), type, svc::PseudoHandle::CurrentProcess, 0));
+                static_assert(std::same_as<size_t, uintptr_t>);
+                AMS_ASSERT(value <= std::numeric_limits<size_t>::max());
+                return static_cast<u64>(value & std::numeric_limits<size_t>::max());
+            }
+        public:
+            constexpr AslrSpaceManagerHorizonImpl() = default;
+
+            static u64 GetHeapSpaceBeginAddress() {
+                return GetAslrInfo(svc::InfoType_HeapRegionAddress);
+            }
+
+            static u64 GetHeapSpaceBeginSize() {
+                return GetAslrInfo(svc::InfoType_HeapRegionSize);
+            }
+
+            static u64 GetAliasSpaceBeginAddress() {
+                return GetAslrInfo(svc::InfoType_AliasRegionAddress);
+            }
+
+            static u64 GetAliasSpaceBeginSize() {
+                return GetAslrInfo(svc::InfoType_AliasRegionSize);
+            }
+
+            static u64 GetAslrSpaceBeginAddress() {
+                if (hos::GetVersion() >= hos::Version_2_0_0 || svc::IsKernelMesosphere()) {
+                    return GetAslrInfo(svc::InfoType_AslrRegionAddress);
+                } else {
+                    if (GetHeapSpaceBeginAddress() < AslrBase64BitDeprecated || GetAliasSpaceBeginAddress() < AslrBase64BitDeprecated) {
+                        return AslrBase32Bit;
+                    } else {
+                        return AslrBase64BitDeprecated;
+                    }
+                }
+            }
+
+            static u64 GetAslrSpaceEndAddress() {
+                if (hos::GetVersion() >= hos::Version_2_0_0 || svc::IsKernelMesosphere()) {
+                    return GetAslrInfo(svc::InfoType_AslrRegionAddress) + GetAslrInfo(svc::InfoType_AslrRegionSize);
+                } else {
+                    if (GetHeapSpaceBeginAddress() < AslrBase64BitDeprecated || GetAliasSpaceBeginAddress() < AslrBase64BitDeprecated) {
+                        return AslrBase32Bit + AslrSize32Bit;
+                    } else {
+                        return AslrBase64BitDeprecated + AslrSize64BitDeprecated;
+                    }
+                }
+            }
+    };
+
+    using AslrSpaceManagerImpl = AslrSpaceManagerHorizonImpl;
+
+}
diff --git a/libraries/libstratosphere/source/os/impl/os_aslr_space_manager_types.hpp b/libraries/libstratosphere/source/os/impl/os_aslr_space_manager_types.hpp
new file mode 100644
index 000000000..19a51a9f2
--- /dev/null
+++ b/libraries/libstratosphere/source/os/impl/os_aslr_space_manager_types.hpp
@@ -0,0 +1,54 @@
+/*
+ * Copyright (c) 2018-2020 Atmosphère-NX
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms and conditions of the GNU General Public License,
+ * version 2, as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+#pragma once
+#include <stratosphere.hpp>
+
+#include "os_address_space_allocator_types.hpp"
+
+#ifdef ATMOSPHERE_OS_HORIZON
+    #include "os_aslr_space_manager_impl.os.horizon.hpp"
+#else
+    #error "Unknown OS for AslrSpaceManagerImpl"
+#endif
+
+namespace ams::os::impl {
+
+    constexpr inline size_t AslrSpaceLargeAlign = 2_MB;
+    constexpr inline size_t AslrSpaceGuardSize  = 4 * MemoryPageSize;
+
+    class AslrSpaceManager {
+        NON_COPYABLE(AslrSpaceManager);
+        NON_MOVEABLE(AslrSpaceManager);
+        private:
+            AddressSpaceAllocator allocator;
+            AslrSpaceManagerImpl impl;
+        public:
+            AslrSpaceManager() : allocator(impl.GetAslrSpaceBeginAddress(), impl.GetAslrSpaceEndAddress(), AslrSpaceGuardSize) { /* ... */ }
+
+            void *AllocateSpace(size_t size) {
+                void *address = this->allocator.AllocateSpace(size, AslrSpaceLargeAlign);
+                if (address == nullptr) {
+                    address = this->allocator.AllocateSpace(size, MemoryPageSize);
+                }
+                return address;
+            }
+
+            bool CheckGuardSpace(uintptr_t address, size_t size) {
+                return this->allocator.CheckGuardSpace(address, size, AslrSpaceGuardSize);
+            }
+    };
+
+}
diff --git a/libraries/libstratosphere/source/os/impl/os_resource_manager.hpp b/libraries/libstratosphere/source/os/impl/os_resource_manager.hpp
index 473b3ddb6..b79babfbf 100644
--- a/libraries/libstratosphere/source/os/impl/os_resource_manager.hpp
+++ b/libraries/libstratosphere/source/os/impl/os_resource_manager.hpp
@@ -18,12 +18,14 @@
 #include "os_rng_manager_impl.hpp"
 #include "os_thread_manager_types.hpp"
 #include "os_tick_manager_impl.hpp"
+#include "os_aslr_space_manager_types.hpp"
 
 namespace ams::os::impl {
 
     class OsResourceManager {
         private:
             RngManager  rng_manager{};
+            AslrSpaceManager aslr_space_manager;
             /* TODO */
             ThreadManager thread_manager{};
             /* TODO */
@@ -33,6 +35,7 @@ namespace ams::os::impl {
             OsResourceManager() = default;
 
             constexpr ALWAYS_INLINE RngManager &GetRngManager() { return this->rng_manager; }
+            constexpr ALWAYS_INLINE AslrSpaceManager &GetAslrSpaceManager() { return this->aslr_space_manager; }
             constexpr ALWAYS_INLINE ThreadManager &GetThreadManager() { return this->thread_manager; }
             constexpr ALWAYS_INLINE TickManager &GetTickManager() { return this->tick_manager; }
     };
diff --git a/libraries/libstratosphere/source/os/os_transfer_memory_api.cpp b/libraries/libstratosphere/source/os/os_transfer_memory_api.cpp
index 747e1492e..e2b438bcc 100644
--- a/libraries/libstratosphere/source/os/os_transfer_memory_api.cpp
+++ b/libraries/libstratosphere/source/os/os_transfer_memory_api.cpp
@@ -16,6 +16,8 @@
 #include <stratosphere.hpp>
 #include "impl/os_thread_manager.hpp"
 #include "impl/os_transfer_memory_impl.hpp"
+#include "impl/os_aslr_space_manager_types.hpp"
+#include "impl/os_aslr_space_manager.hpp"
 
 namespace ams::os {
 
@@ -131,7 +133,7 @@ namespace ams::os {
         for (int i = 0; i < 64; ++i) {
             /* Reserve space to map the memory. */
             /* TODO: os::AslrSpaceManager */
-            void *map_address = ::virtmemReserve(tmem->size);
+            void *map_address = impl::GetAslrSpaceManager().AllocateSpace(tmem->size);
             R_UNLESS(map_address != nullptr, os::ResultOutOfAddressSpace());
 
             /* Mark allocated. */
@@ -144,8 +146,13 @@ namespace ams::os {
                 R_CATCH(os::ResultInvalidCurrentMemoryState) { continue; }
             } R_END_TRY_CATCH;
 
-            /* TODO: Check guard space via aslr manager. */
-            if (false /* !impl::GetAslrSpaceManager()->CheckGuardSpace(reinterpret_cast<uintptr_t>(tmem->address), tmem->size) */) {
+            /* Check guard space via aslr manager. */
+            if (!impl::GetAslrSpaceManager().CheckGuardSpace(reinterpret_cast<uintptr_t>(tmem->address), tmem->size)) {
+                /* NOTE: Nintendo bug here. If this case occurs, they will return ResultSuccess() without actually mapping the transfer memory. */
+                /* This is because they basically do if (!os::ResultInvalidCurrentMemoryState::Includes(result)) { return result; }, and */
+                /* ResultSuccess() is not included by ResultInvalidCurrentMemoryState. */
+
+                /* We will do better than them, and will not falsely return ResultSuccess(). */
                 impl::TransferMemoryImpl::Unmap(tmem->handle, tmem->address, tmem->size);
                 continue;
             }