> On Jun 5, 2023, at 9:10 AM, Edgecombe, Rick P <rick.p.edgecombe@xxxxxxxxx> wrote: > > On Mon, 2023-06-05 at 11:11 +0300, Mike Rapoport wrote: >> On Sun, Jun 04, 2023 at 10:52:44PM -0400, Steven Rostedt wrote: >>> On Thu, 1 Jun 2023 16:54:36 -0700 >>> Nadav Amit <nadav.amit@xxxxxxxxx> wrote: >>> >>>>> The way text_poke() is used here, it is creating a new writable >>>>> alias >>>>> and flushing it for *each* write to the module (like for each >>>>> write of >>>>> an individual relocation, etc). I was just thinking it might >>>>> warrant >>>>> some batching or something. >> >>>> I am not advocating to do so, but if you want to have many >>>> efficient >>>> writes, perhaps you can just disable CR0.WP. Just saying that if >>>> you >>>> are about to write all over the memory, text_poke() does not >>>> provide >>>> too much security for the poking thread. >> >> Heh, this is definitely and easier hack to implement :) > > I don't know the details, but previously there was some strong dislike > of CR0.WP toggling. And now there is also the problem of CET. Setting > CR0.WP=0 will #GP if CR4.CET is 1 (as it currently is for kernel IBT). > I guess you might get away with toggling them both in some controlled > situation, but it might be a lot easier to hack up then to be made > fully acceptable. It does sound much more efficient though. Thanks for highlighting this issue. I understand the limitations of CR0.WP. There is also always the concerns that without CET or other control flow integrity mechanism, someone would abuse (using ROP/JOP) functions that clear CR0.WP…
