Isolation

Cybersecurity 19 Sep 2026 6 min read

userfaultfd Write Protection Moves Memory Writes Behind a User-Space Fault Boundary

A thread can hold a writable virtual memory mapping and still block when it attempts to modify a particular page. Linux userfaultfd write-protect mode lets user space register a memory range, apply write protection to pages in that range, and receive a page-fault event when a protected page is written. The VMA can remain logically writable while page-table state creates a narrower interception boundary. This mechanism is not a general authorization system. It is a memory-fault control interface. Its security relevance comes from the placement of the decision point: a write can be suspended before the protected page changes, allowing a separate handler to record state, coordinate migration, preserve a snapshot boundary, or reject progress by leaving the fault unresolved.

Cybersecurity Linux

Database 02 Sep 2026 5 min read

Understanding Write Skew and Transaction Isolation

Transaction isolation is often explained with dirty reads and lost updates, but another anomaly is especially important for multi-row business rules: write skew. Write skew occurs when concurrent transactions read the same valid state, make decisions independently, and update different rows in a way that produces an invalid combined state. Because they do not overwrite the same row, ordinary write-conflict detection may not stop them. A simple invariant Imagine an on-call table where at least one doctor must remain available:

Database Transactions