From 7cbe9579ba2e38ca003d7400a160fba55ee35c50 Mon Sep 17 00:00:00 2001
From: Ryan Houdek <Sonicadvance1@gmail.com>
Date: Sun, 20 Jun 2021 01:37:11 -0700
Subject: [PATCH] Fixes 32-bit allocator returning 64-bit pointers on old
 kernels

In the case of a kernel older than 4.17 then MAP_FIXED_NOREPLACE doesn't exist.
This adds a check in to see if the pointer returned was valid but not what we asked for
---
 Source/Tests/LinuxSyscalls/x32/Syscalls.cpp | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/Source/Tests/LinuxSyscalls/x32/Syscalls.cpp b/Source/Tests/LinuxSyscalls/x32/Syscalls.cpp
index 3ccf756c2..7f02d175a 100644
--- a/Source/Tests/LinuxSyscalls/x32/Syscalls.cpp
+++ b/Source/Tests/LinuxSyscalls/x32/Syscalls.cpp
@@ -207,7 +207,15 @@ restart:
             errno != EEXIST) {
           return reinterpret_cast<void*>(-errno);
         }
-        else if (MappedPtr == MAP_FAILED) {
+        else if (MappedPtr == MAP_FAILED ||
+                 MappedPtr >= reinterpret_cast<void*>(TOP_KEY << PAGE_SHIFT)) {
+          // Handles the case where MAP_FIXED_NOREPLACE failed with MAP_FAILED
+          // or if the host system's kernel isn't new enough then it returns the wrong pointer
+          if (MappedPtr >= reinterpret_cast<void*>(TOP_KEY << PAGE_SHIFT)) {
+            // Make sure to munmap this so we don't leak memory
+            ::munmap(MappedPtr, length);
+          }
+
           if (UpperPage == TOP_KEY) {
             BottomPage = BASE_KEY;
             Wrapped = true;