Kernel: Add memory scrubbing in slab_alloc() and slab_dealloc()

These now scrub allocated and freed memory like kmalloc()/kfree() was
already doing.

Kernel/Arch/i386/CPU.cpp

@@ -319,6 +319,8 @@ void page_fault_handler(RegisterDump regs)
         u32 free_scrub_pattern = explode_byte(FREE_SCRUB_BYTE);
         u32 kmalloc_scrub_pattern = explode_byte(KMALLOC_SCRUB_BYTE);
         u32 kfree_scrub_pattern = explode_byte(KFREE_SCRUB_BYTE);
+        u32 slab_alloc_scrub_pattern = explode_byte(SLAB_ALLOC_SCRUB_BYTE);
+        u32 slab_dealloc_scrub_pattern = explode_byte(SLAB_DEALLOC_SCRUB_BYTE);
         if ((fault_address & 0xffff0000) == (malloc_scrub_pattern & 0xffff0000)) {
             kprintf("\033[33;1mNote: Address %p looks like it may be uninitialized malloc() memory\033[0m\n", fault_address);
         } else if ((fault_address & 0xffff0000) == (free_scrub_pattern & 0xffff0000)) {
@@ -327,6 +329,10 @@ void page_fault_handler(RegisterDump regs)
             kprintf("\033[33;1mNote: Address %p looks like it may be uninitialized kmalloc() memory\033[0m\n", fault_address);
         } else if ((fault_address & 0xffff0000) == (kfree_scrub_pattern & 0xffff0000)) {
             kprintf("\033[33;1mNote: Address %p looks like it may be recently kfree()'d memory\033[0m\n", fault_address);
+        } else if ((fault_address & 0xffff0000) == (slab_alloc_scrub_pattern & 0xffff0000)) {
+            kprintf("\033[33;1mNote: Address %p looks like it may be uninitialized slab_alloc() memory\033[0m\n", fault_address);
+        } else if ((fault_address & 0xffff0000) == (slab_dealloc_scrub_pattern & 0xffff0000)) {
+            kprintf("\033[33;1mNote: Address %p looks like it may be recently slab_dealloc()'d memory\033[0m\n", fault_address);
         } else if (fault_address < 4096) {
             kprintf("\033[33;1mNote: Address %p looks like a possible nullptr dereference\033[0m\n", fault_address);
         }

Kernel/Heap/SlabAllocator.cpp

@@ -61,6 +61,9 @@ public:
         m_freelist = m_freelist->next;
         ++m_num_allocated;
         --m_num_free;
+#ifdef SANITIZE_KMALLOC
+        memset(ptr, SLAB_ALLOC_SCRUB_BYTE, slab_size());
+#endif
         return ptr;
     }
 
@@ -73,6 +76,10 @@ public:
             return;
         }
         ((FreeSlab*)ptr)->next = m_freelist;
+#ifdef SANITIZE_KMALLOC
+        if (slab_size() > sizeof(FreeSlab*))
+            memset(((FreeSlab*)ptr)->padding, SLAB_DEALLOC_SCRUB_BYTE, sizeof(FreeSlab::padding));
+#endif
         m_freelist = (FreeSlab*)ptr;
         ++m_num_allocated;
         --m_num_free;

Kernel/Heap/SlabAllocator.h

@@ -29,6 +29,9 @@
 #include <AK/Function.h>
 #include <AK/Types.h>
 
+#define SLAB_ALLOC_SCRUB_BYTE 0xab
+#define SLAB_DEALLOC_SCRUB_BYTE 0xbc
+
 class JsonObjectSerializer;
 
 void* slab_alloc(size_t slab_size);