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 ?
