On 13.07.2018 23:32, Jason Thorpe wrote: > > >> On Jul 13, 2018, at 2:22 PM, Kamil Rytarowski <[email protected]> wrote: >> >> On 13.07.2018 23:10, Jaromír Doleček wrote: >>> 2018-07-13 22:54 GMT+02:00 Kamil Rytarowski <[email protected]>: >>>> I disagree with disabling it. The code is not broken, it's covered by >>>> tests, it's in use. >>> >>> This looks like perfect candidate for optional (default off) feature. >>> It is useless and dangerous for general purpose use by virtue of being >>> root only, but useful for specialized use. >>> >>> Honestly, I don't see any reason to have this on by default. > > A sysctl is kind of lame, because it can also result in a branch prediction > miss. > > Protect the sysctl in an #ifdef to enable being able to enable the feature? >
This sysctl does not disable the feature in the kernel, it is designed to control the security extension value whether a user is allowed to set these registers. A user is still allowed to read them always. security.models.extensions.user_set_dbregs = 0 # <- here DB registers It's integrated into the security framework in the kernel that checks whether write operation is allowed. #ifdefing it out in a non-benchmarking application (I was checking ones that do something with syscalls) is more negligible than 0,3% of overhead in the kernel in a loop. However if there is a general consensus that this is a must-have and urgent, I can dedicate time for this.. CC: Christos / Alistair.
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