diff --git a/kernel/src/arch/riscv/vspace/traits.rs b/kernel/src/arch/riscv/vspace/traits.rs
index adc0421..f515705 100644
--- a/kernel/src/arch/riscv/vspace/traits.rs
+++ b/kernel/src/arch/riscv/vspace/traits.rs
@@ -1,5 +1,6 @@
 use num_traits::ToPrimitive;
 use utils::size::{GIB, KIB, MIB, TIB};
+use utils::MASK;
 use vspace::addr::{AddressOps, PhysAddr, VirtAddr};
 use vspace::paging::TableLevel;
 
@@ -8,8 +9,8 @@ pub trait PhysAddrPaging {
     const PPN_BITS: usize;
     const PPN_OFFSET: usize;
 
-    const PA_PPN_MASK: usize = ((1 << Self::PPN_BITS) - 1) << Self::PG_OFFSET;
-    const PTE_PPN_MASK: usize = ((1 << Self::PPN_BITS) - 1) << Self::PPN_OFFSET;
+    const PA_PPN_MASK: usize = MASK!(Self::PPN_BITS) << Self::PG_OFFSET;
+    const PTE_PPN_MASK: usize = MASK!(Self::PPN_BITS) << Self::PPN_OFFSET;
 
     fn to_ppn(&self) -> usize
     where Self: AddressOps {
@@ -61,7 +62,7 @@ pub trait VirtAddrPaging {
 
     fn lower_bits(&self, level: usize) -> usize
     where Self: AddressOps {
-        self.as_usize() & ((1 << (Self::PG_OFFSET + Self::VPN_BITS * (level + 1))) - 1)
+        self.as_usize() & MASK!(Self::PG_OFFSET + Self::VPN_BITS * (level + 1))
     }
 }
 
diff --git a/lib/utils/src/bin.rs b/lib/utils/src/bin.rs
new file mode 100644
index 0000000..fd20624
--- /dev/null
+++ b/lib/utils/src/bin.rs
@@ -0,0 +1,6 @@
+#[macro_export]
+macro_rules! MASK {
+    ($bits:expr) => {
+        (1 << $bits) - 1
+    };
+}
diff --git a/lib/utils/src/lib.rs b/lib/utils/src/lib.rs
index 2fc00c5..3130303 100644
--- a/lib/utils/src/lib.rs
+++ b/lib/utils/src/lib.rs
@@ -3,6 +3,7 @@
 
 pub mod assert;
 pub mod atomic;
+pub mod bin;
 pub mod container_of;
 pub mod extern_addr;
 pub mod function_name;