On 10/13/2017 01:03 AM, Mathieu Desnoyers wrote:
Expose a new system call allowing each thread to register one userspace memory area to be used as an ABI between kernel and user-space for two purposes: user-space restartable sequences and quick access to read the current CPU number value from user-space. * Restartable sequences (per-cpu atomics) Restartables sequences allow user-space to perform update operations on per-cpu data without requiring heavy-weight atomic operations. The restartable critical sections (percpu atomics) work has been started by Paul Turner and Andrew Hunter. It lets the kernel handle restart of critical sections. [1] [2] The re-implementation proposed here brings a few simplifications to the ABI which facilitates porting to other architectures and speeds up the user-space fast path. A locking-based fall-back, purely implemented in user-space, is proposed here to deal with debugger single-stepping. This fallback interacts with rseq_start() and rseq_finish(), which force retries in response to concurrent lock-based activity.
This functionality essentially relies on writable function pointers (or pointers to data containing function pointers), right? Is there a way to make this a less attractive target for exploit writers?
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