On 01/11/2019 02:52 PM, Thomas Gleixner wrote: > On Wed, 19 Dec 2018, Waiman Long wrote: > >> With the default SPEC_STORE_BYPASS_SECCOMP/SPEC_STORE_BYPASS_PRCTL mode, >> the TIF_SSBD bit will be inherited when a new task is fork'ed or cloned. >> >> As only certain class of applications (like Java) requires disabling >> speculative store bypass for security purpose, it may not make sense to >> allow the TIF_SSBD bit to be inherited across execve() boundary where the >> new application may not need SSBD at all and is probably not aware that >> SSBD may have been turned on. This may cause an unnecessary performance >> loss of up to 20% in some cases. > Lot's of MAY's here. Aside of that this fundamentally changes the > behaviour. I'm not really a fan of doing that. > > If there are good reasons to have a non-inherited variant, then we rather > introduce that instead of changing the existing semantics without a way for > existing userspace to notice. I understand your point. How about adding a ",noexec" auxillary option to the spec_store_bypass_disable command line to activate this new behavior without changing the default. Will that be acceptable? Cheers, Longman
