Make mprotect&munmap return fast when len is zero

kernel/src/syscall/mprotect.rs

@@ -12,7 +12,17 @@ pub fn sys_mprotect(addr: Vaddr, len: usize, perms: u64, ctx: &Context) -> Resul
         addr, len, vm_perms
     );
     let root_vmar = ctx.process.root_vmar();
-    debug_assert!(addr % PAGE_SIZE == 0);
+
+    // According to linux behavior,
+    // <https://elixir.bootlin.com/linux/v6.0.9/source/mm/mprotect.c#L681>,
+    // the addr is checked even if len is 0.
+    if addr % PAGE_SIZE != 0 {
+        return_errno_with_message!(Errno::EINVAL, "the start address should be page aligned");
+    }
+    if len == 0 {
+        return Ok(SyscallReturn::Return(0));
+    }
+
     let len = len.align_up(PAGE_SIZE);
     let range = addr..(addr + len);
     root_vmar.protect(vm_perms, range)?;

kernel/src/syscall/munmap.rs

@@ -7,6 +7,14 @@ use crate::prelude::*;
 
 pub fn sys_munmap(addr: Vaddr, len: usize, ctx: &Context) -> Result<SyscallReturn> {
     debug!("addr = 0x{:x}, len = {}", addr, len);
+
+    if addr % PAGE_SIZE != 0 {
+        return_errno_with_message!(Errno::EINVAL, "munmap addr must be page-aligned");
+    }
+    if len == 0 {
+        return_errno_with_message!(Errno::EINVAL, "munmap len cannot be zero");
+    }
+
     let root_vmar = ctx.process.root_vmar();
     let len = len.align_up(PAGE_SIZE);
     debug!("unmap range = 0x{:x} - 0x{:x}", addr, addr + len);