On 01/08/2018 08:12 AM, Willy Tarreau wrote: > Since we're going to keep running on the same PGD when returning to > userspace for certain performance-critical tasks, we'll need the user > pages to be executable. So this code disables the extra protection > that was added consisting in marking user pages _PAGE_NX so that this > pgd remains usable for userspace. > > Note: it isn't necessarily the best approach, but one way or another > if we want to be able to return to userspace from the kernel, > we'll have to have this executable anyway. Another approach > might consist in using another pgd for userland+kernel but > the current core really looks like an extra careful measure > to catch early bugs if any.
I don't like this. I think the prctl() should apply to an entire process, not to a thread. If it applies to a process, you can unpoison the PGD. I even had code to do this in an earlier version of the (whole system) runtime PTI on/off stuff. Why are you even posting half-baked hacks like this now? Is there something super-pressing about this set that we need to lock in a new ABI now?
