Messages in this thread | | | Date | Fri, 12 Sep 2014 11:24:49 +0200 (CEST) | From | Thomas Gleixner <> | Subject | Re: [PATCH v8 08/10] x86, mpx: add prctl commands PR_MPX_REGISTER, PR_MPX_UNREGISTER |
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On Fri, 12 Sep 2014, Thomas Gleixner wrote: > On Thu, 11 Sep 2014, Dave Hansen wrote: > > Well, we use it to figure out whether we _potentially_ need to tear down > > an VM_MPX-flagged area. There's no guarantee that there will be one. > > So what you are saying is, that if user space sets the pointer to NULL > via the unregister prctl, kernel can safely ignore vmas which have the > VM_MPX flag set. I really can't follow that logic. > > mmap_mpx(); > prctl(enable mpx); > do lots of crap which uses mpx; > prctl(disable mpx); > > So after that point the previous use of MPX is irrelevant, just > because we set a pointer to NULL? Does it just look like crap because > I do not get the big picture how all of this is supposed to work?
do_bounds() will happily map new BTs no matter whether the prctl was invoked or not. So what's the value of the prctl at all?
The mapping is flagged VM_MPX. Why is this not sufficient?
Thanks,
tglx
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