> On Aug 22, 2022, at 11:39 PM, Christophe Leroy <christophe.leroy@xxxxxxxxxx> wrote: > > > > Le 23/08/2022 à 07:42, Peter Zijlstra a écrit : >> On Mon, Aug 22, 2022 at 04:56:47PM +0000, Song Liu wrote: >>> >>> >>>> On Aug 22, 2022, at 9:34 AM, Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote: >>>> >>>> On Mon, Aug 22, 2022 at 03:46:38PM +0000, Song Liu wrote: >>>>> Could you please share your feedback on this? >>>> >>>> I've looked at it all of 5 minutes, so perhaps I've missed something. >>>> >>>> However, I'm a little surprised you went with a second tree instead of >>>> doing the top-down thing for data. The way you did it makes it hard to >>>> have guard pages between text and data. >>> >>> I didn't realize the importance of the guard pages. But it is not too >> >> I'm not sure how important it is, just seems like a good idea to trap >> anybody trying to cross that divide. Also, to me it seems like a good >> idea to have a single large contiguous text region instead of splintered >> 2M pages. >> >>> hard to do it with this approach. For each 2MB text page, we can reserve >>> 4kB on the beginning and end of it. Would this work? >> >> Typically a guard page has different protections (as in none what so >> ever) so that every access goes *splat*. > > > Text is RO-X, on some architectures even only X. So the only real thing > to protect against is bad execution, isn't it ?. So I guess having some > areas with invalid or trap instructions would be enough ? Agreed that filling with trap instructions should be enough. Thanks, Song
