Bitmap: Add a fallible variant of match_region() that does not crash if arguments are out of range

This lets us call deallocate_memory() with any address and it will not crash.

kernel/src/memory/UserVM.cpp

@@ -97,7 +97,7 @@ Result<void> UserVM::free_several_pages(u64 address, usize count)
     const u64 index = (address - VM_BASE) / ARCH_PAGE_SIZE;
     if ((index + count) > (MAX_VM_SIZE * 8)) return err(EINVAL);
 
-    if (!m_bitmap.match_region(index, count, true)) return err(EFAULT);
+    if (!TRY(m_bitmap.try_match_region(index, count, true))) return err(EFAULT);
 
     m_bitmap.clear_region(index, count, false);
 

luna/include/luna/Bitmap.h

@@ -50,6 +50,7 @@ class Bitmap
     Option<usize> find_and_toggle_region(bool value, usize count, usize begin = 0);
 
     bool match_region(usize start, usize bits, bool value);
+    Result<bool> try_match_region(usize start, usize bits, bool value);
 
     void clear(bool value);
     void clear_region(usize start, usize bits, bool value);
@@ -60,6 +61,8 @@ class Bitmap
         return b ? 0xff : 0;
     }
 
+    bool match_region_impl(usize start, usize bits, bool value);
+
     u8* m_location = nullptr;
     usize m_size_in_bytes = 0;
 };

luna/src/Bitmap.cpp

@@ -187,11 +187,8 @@ Option<usize> Bitmap::find_and_toggle_region(bool value, usize count, usize begi
     return index;
 }
 
-bool Bitmap::match_region(usize start, usize bits, bool value)
+bool Bitmap::match_region_impl(usize start, usize bits, bool value)
 {
-    expect(initialized(), "Bitmap was never initialized");
-    expect((start + bits) <= size(), "Bitmap match out of range");
-
     if (!bits) return true;
 
     // Match individual bits while not on a byte boundary.
@@ -223,3 +220,19 @@ bool Bitmap::match_region(usize start, usize bits, bool value)
 
     return true;
 }
+
+bool Bitmap::match_region(usize start, usize bits, bool value)
+{
+    expect(initialized(), "Bitmap was never initialized");
+    expect((start + bits) <= size(), "Bitmap match out of range");
+
+    return match_region_impl(start, bits, value);
+}
+
+Result<bool> Bitmap::try_match_region(usize start, usize bits, bool value)
+{
+    expect(initialized(), "Bitmap was never initialized");
+    if ((start + bits) > size()) return err(EINVAL);
+
+    return match_region_impl(start, bits, value);
+}