From 708c5daad954f9339732ed86147a4cdee7980785 Mon Sep 17 00:00:00 2001
From: LDA <lda@ari.lt>
Date: Thu, 24 Oct 2024 11:41:33 +0200
Subject: [PATCH] [FIX] Fix memory alignment issues

Some architectures(DEC Alpha as a main outlier, but x86 may behave that
way by setting flags) raise traps on unaligned operations, which can be
either costly(having to talk to the kernel, which may have to emulate
the read) or could cause program termination.

Also adds a basic memory interval for checking if a pointer has any
business living within the heap. Most systems separate those anyways so
it avoids doing potentially dangerous operations.
---
 src/Memory.c | 69 +++++++++++++++++++++++++++++++++++++++-------------
 1 file changed, 52 insertions(+), 17 deletions(-)

diff --git a/src/Memory.c b/src/Memory.c
index 31d8050..e31ec27 100644
--- a/src/Memory.c
+++ b/src/Memory.c
@@ -42,26 +42,30 @@
 
 #define MEMORY_FILE_SIZE 256
 
+#define MEM_BOUND_TYPE uint64_t
+#define MEM_BOUND 0xDEADBEEFBEEFDEAD
+#define MEM_MAGIC 0xDEADBEEFDEADBEEF
+
 struct MemoryInfo
 {
     uint64_t magic;
 
     size_t size;
+    size_t unalignedSize;
     char file[MEMORY_FILE_SIZE];
     int line;
     void *pointer;
 
     MemoryInfo *prev;
     MemoryInfo *next;
+
+    MEM_BOUND_TYPE leftBoundary;
 };
 
-#define MEM_BOUND_TYPE uint32_t
-#define MEM_BOUND 0xDEADBEEF
-#define MEM_MAGIC 0xDEADBEEFDEADBEEF
+#define MEM_SIZE_ACTUAL(x) (MemoryAlignBoundary((x) * sizeof(uint8_t)) + sizeof(MEM_BOUND_TYPE))
+#define MEM_START_BOUNDARY(info) (info->leftBoundary)
+#define MEM_END_BOUNDARY(info) (*(((MEM_BOUND_TYPE *) (((uint8_t *) info->pointer) + info->size)) - 1))
 
-#define MEM_BOUND_LOWER(p) *((MEM_BOUND_TYPE *) p)
-#define MEM_BOUND_UPPER(p, x) *(((MEM_BOUND_TYPE *) (((uint8_t *) p) + x)) + 1)
-#define MEM_SIZE_ACTUAL(x) (((x) * sizeof(uint8_t)) + (2 * sizeof(MEM_BOUND_TYPE)))
 
 static pthread_mutex_t lock;
 static void (*hook) (MemoryAction, MemoryInfo *, void *) = MemoryDefaultHook;
@@ -71,6 +75,19 @@ static size_t allocationsLen = 0;
 
 static MemoryInfo *allocationTail = NULL;
 
+/* Simple range of "plausible" boundaries for heap, serving as an extra 
+ * check */
+static void *heapStart, *heapEnd;
+
+static size_t MemoryAlignBoundary(size_t size)
+{
+    size_t boundSize = sizeof(MEM_BOUND_TYPE);
+    size_t remainder = size % boundSize;
+    size_t closest   = size / boundSize + !!remainder;
+
+    return closest * boundSize;
+}
+
 int
 MemoryRuntimeInit(void)
 {
@@ -85,6 +102,8 @@ MemoryRuntimeInit(void)
     pthread_mutexattr_settype(&attr, PTHREAD_MUTEX_RECURSIVE);
     ret = pthread_mutex_init(&lock, &attr);
     pthread_mutexattr_destroy(&attr);
+    heapStart = NULL;
+    heapEnd = NULL;
 
     ret = (ret == 0);
 
@@ -110,6 +129,15 @@ MemoryInsert(MemoryInfo * a)
     a->prev = allocationTail;
     a->magic = MEM_MAGIC;
 
+    if (!heapStart || heapStart > (void *) a)
+    {
+        heapStart = a;
+    }
+    if (!heapEnd || heapEnd < (void *) a)
+    {
+        heapEnd = a;
+    }
+
     allocationTail = a;
     allocationsLen++;
 
@@ -142,8 +170,9 @@ MemoryDelete(MemoryInfo * a)
 static int
 MemoryCheck(MemoryInfo * a)
 {
-    if (MEM_BOUND_LOWER(a->pointer) != MEM_BOUND ||
-        MEM_BOUND_UPPER(a->pointer, a->size - (2 * sizeof(MEM_BOUND_TYPE))) != MEM_BOUND)
+    if (MEM_START_BOUNDARY(a) != MEM_BOUND || 
+        a->magic != MEM_MAGIC ||
+        MEM_END_BOUNDARY(a) != MEM_BOUND)
     {
         if (hook)
         {
@@ -174,13 +203,14 @@ MemoryAllocate(size_t size, const char *file, int line)
     p = a + 1;
 
     memset(p, 0, MEM_SIZE_ACTUAL(size));
-    MEM_BOUND_LOWER(p) = MEM_BOUND;
-    MEM_BOUND_UPPER(p, size) = MEM_BOUND;
 
     a->size = MEM_SIZE_ACTUAL(size);
+    a->unalignedSize = size;
     strncpy(a->file, file, MEMORY_FILE_SIZE - 1);
     a->line = line;
     a->pointer = p;
+    MEM_START_BOUNDARY(a) = MEM_BOUND;
+    MEM_END_BOUNDARY(a) = MEM_BOUND;
 
     if (!MemoryInsert(a))
     {
@@ -195,7 +225,7 @@ MemoryAllocate(size_t size, const char *file, int line)
     }
 
     pthread_mutex_unlock(&lock);
-    return ((MEM_BOUND_TYPE *) p) + 1;
+    return p;
 }
 
 void *
@@ -220,6 +250,7 @@ MemoryReallocate(void *p, size_t size, const char *file, int line)
         if (new)
         {
             a = new;
+            a->unalignedSize = size;
             a->size = MEM_SIZE_ACTUAL(size);
             strncpy(a->file, file, MEMORY_FILE_SIZE - 1);
             a->line = line;
@@ -228,8 +259,8 @@ MemoryReallocate(void *p, size_t size, const char *file, int line)
             a->pointer = a + 1;
             MemoryInsert(a);
 
-            MEM_BOUND_LOWER(a->pointer) = MEM_BOUND;
-            MEM_BOUND_UPPER(a->pointer, size) = MEM_BOUND;
+            MEM_START_BOUNDARY(a) = MEM_BOUND;
+            MEM_END_BOUNDARY(a) = MEM_BOUND;
 
             if (hook)
             {
@@ -253,7 +284,7 @@ MemoryReallocate(void *p, size_t size, const char *file, int line)
         }
     }
 
-    return ((MEM_BOUND_TYPE *) a->pointer) + 1;
+    return a->pointer;
 }
 
 void
@@ -344,8 +375,12 @@ MemoryInfoGet(void *po)
 
     pthread_mutex_lock(&lock);
 
-    p = ((MEM_BOUND_TYPE *) po) - 1;
     p = ((MemoryInfo *) p) - 1;
+    if (p < heapStart || p > heapEnd)
+    {
+        pthread_mutex_unlock(&lock);
+        return NULL;
+    }
 
     if (((MemoryInfo *)p)->magic != MEM_MAGIC)
     {
@@ -364,7 +399,7 @@ MemoryInfoGetSize(MemoryInfo * a)
         return 0;
     }
 
-    return a->size ? a->size - (2 * sizeof(MEM_BOUND_TYPE)) : 0;
+    return a->size ? a->unalignedSize : 0;
 }
 
 const char *
@@ -397,7 +432,7 @@ MemoryInfoGetPointer(MemoryInfo * a)
         return NULL;
     }
 
-    return ((MEM_BOUND_TYPE *) a->pointer) + 1;
+    return a->pointer;
 }
 
 void
-- 
2.45.2