Fix - Gapped memory vm_addr_end (#472)

* Adds test_gapped_map.

* Fixes vm_addr_end to be double the length if region is gapped.

* Adds missing break statement in slow path while loop.

src/memory_region.rs

@@ -67,17 +67,19 @@ pub struct MemoryRegion {
 
 impl MemoryRegion {
     fn new(slice: &[u8], vm_addr: u64, vm_gap_size: u64, state: MemoryState) -> Self {
+        let mut vm_addr_end = vm_addr.saturating_add(slice.len() as u64);
         let mut vm_gap_shift = (std::mem::size_of::<u64>() as u8)
             .saturating_mul(8)
             .saturating_sub(1);
         if vm_gap_size > 0 {
+            vm_addr_end = vm_addr_end.saturating_add(slice.len() as u64);
             vm_gap_shift = vm_gap_shift.saturating_sub(vm_gap_size.leading_zeros() as u8);
             debug_assert_eq!(Some(vm_gap_size), 1_u64.checked_shl(vm_gap_shift as u32));
         };
         MemoryRegion {
             host_addr: Cell::new(slice.as_ptr() as u64),
             vm_addr,
-            vm_addr_end: vm_addr.saturating_add(slice.len() as u64),
+            vm_addr_end,
             len: slice.len() as u64,
             vm_gap_shift,
             state: Cell::new(state),
@@ -151,7 +153,7 @@ impl fmt::Debug for MemoryRegion {
             self.host_addr,
             self.host_addr.get().saturating_add(self.len),
             self.vm_addr,
-            self.vm_addr.saturating_add(self.len),
+            self.vm_addr_end,
             self.len
         )
     }
@@ -242,7 +244,7 @@ impl<'a> UnalignedMemoryMapping<'a> {
         for index in 1..regions.len() {
             let first = &regions[index.saturating_sub(1)];
             let second = &regions[index];
-            if first.vm_addr.saturating_add(first.len) > second.vm_addr {
+            if first.vm_addr_end > second.vm_addr {
                 return Err(EbpfError::InvalidMemoryRegion(index));
             }
         }
@@ -302,10 +304,7 @@ impl<'a> UnalignedMemoryMapping<'a> {
             // we check for index==0 above, and by construction if we get here index
             // must be contained in region
             let region = unsafe { self.regions.get_unchecked(index - 1) };
-            cache.insert(
-                region.vm_addr..region.vm_addr.saturating_add(region.len),
-                index,
-            );
+            cache.insert(region.vm_addr..region.vm_addr_end, index);
             Some(region)
         }
     }
@@ -390,6 +389,8 @@ impl<'a> UnalignedMemoryMapping<'a> {
                     Some(region) => region,
                     None => break,
                 };
+            } else {
+                break;
             }
         }
 
@@ -461,6 +462,8 @@ impl<'a> UnalignedMemoryMapping<'a> {
                     Some(region) => region,
                     None => break,
                 };
+            } else {
+                break;
             }
         }
 
@@ -987,6 +990,38 @@ mod test {
         );
     }
 
+    #[test]
+    fn test_gapped_map() {
+        for aligned_memory_mapping in [false, true] {
+            let config = Config {
+                aligned_memory_mapping,
+                ..Config::default()
+            };
+            let mut mem1 = vec![0xff; 8];
+            let m = MemoryMapping::new(
+                vec![
+                    MemoryRegion::new_readonly(&[0; 8], ebpf::MM_PROGRAM_START),
+                    MemoryRegion::new_writable_gapped(&mut mem1, ebpf::MM_STACK_START, 2),
+                ],
+                &config,
+            )
+            .unwrap();
+            for frame in 0..4 {
+                let address = ebpf::MM_STACK_START + frame * 4;
+                assert!(m.region(AccessType::Load, address).is_ok());
+                assert!(m.map(AccessType::Load, address, 2, 0).is_ok());
+                assert_error!(
+                    m.map(AccessType::Load, address + 2, 2, 0),
+                    "AccessViolation"
+                );
+                assert_eq!(m.load::<u16>(address, 0).unwrap(), 0xFFFF);
+                assert_error!(m.load::<u16>(address + 2, 0), "AccessViolation");
+                assert!(m.store::<u16>(0xFFFF, address, 0).is_ok());
+                assert_error!(m.store::<u16>(0xFFFF, address + 2, 0), "AccessViolation");
+            }
+        }
+    }
+
     #[test]
     fn test_unaligned_map_overlap() {
         let config = Config::default();