> A maximum limit of 16 operations per cpu_opv syscall invocation is > enforced, so user-space cannot generate a too long preempt-off critical > section. Except that all the operations could be going to mmapped I/O space and if I pick the right targets could take quite a long time to complete. It's still only 16 operations - But 160ms is a lot worse than 10ms. In fact with compare_iter I could make it much much worse still as I get 2 x TMP_BUFLEN x 16 x worst case latency in my attack. That's enough to screw up plenty of things. So it seems to me at minimum it needs to be restricted to genuine RAM user pages, and in fact would be far far simpler code as well if it were limited to a single page for a given invocation or if like futexes you had to specifically create a per_cpu_opv mapping. Alan -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
