On Wed, 2018-01-31 at 08:03 +0100, Dominik Brodowski wrote: > Whether a process needs protection by IBPB on context switches is a > different question to whether a process should be allowed to be dumped, > though the former may be a superset of the latter. Enable IBPB on all > context switches to a different userspace process, until we have a clear > mitigation strategy for userspace against Spectre-v2 designed and > implemented. > > ... > if (tsk && tsk->mm && > - tsk->mm->context.ctx_id != last_ctx_id && > - get_dumpable(tsk->mm) != SUID_DUMP_USER) > + tsk->mm->context.ctx_id != last_ctx_id) > indirect_branch_prediction_barrier();
I understand your argument and I sympathise. But that's going to hurt a *lot*, and we don't even have a viable proof-of-concept for a user←→user Spectre v2 attack, do we? It's only theoretical? Show a working PoC and it makes the argument somewhat more convincing...
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