On Tue 04-07-17 13:21:02, Ben Hutchings wrote: > On Tue, 2017-07-04 at 14:00 +0200, Michal Hocko wrote: > > On Tue 04-07-17 12:36:11, Ben Hutchings wrote: > > > On Tue, 2017-07-04 at 12:42 +0200, Michal Hocko wrote: > > > > On Tue 04-07-17 11:47:28, Willy Tarreau wrote: > > > > > On Tue, Jul 04, 2017 at 11:35:38AM +0200, Michal Hocko wrote: > > > > > > [...] > > > > > But wouldn't this completely disable the check in case such a guard > > > > > page > > > > > is installed, and possibly continue to allow the collision when the > > > > > stack > > > > > allocation is large enough to skip this guard page ? > > > > > > > > Yes and but a PROT_NONE would fault and as the changelog says, we _hope_ > > > > that userspace does the right thing. > > > > > > It may well not be large enough, because of the same wrong assumptions > > > that resulted in the kernel's guard page not being large enough. We > > > should count it as part of the guard gap but not a substitute. > > > > yes, you are right of course. But isn't this a bug on their side > > considering they are managing their _own_ stack gap? > > Yes it's their bug, but you know the rule - don't break user-space.
Absolutely, that is why I belive we should consider the prev VMA but doing anything more just risks for new regressions. Or why do you think that not-checking them would cause a regression? > > Our stack gap > > management is a best effort thing and two such approaches competing will > > always lead to weird cornercases. That was my assumption when saying > > that I am not sure this is really _worth_ it. We should definitely try > > to workaround clashes but that's about it. If others think that we > > should do everything to prevent even those issues I will not oppose > > of course. It just adds more cycles to something that is a weird case > > already. > > I don't want odd behaviour to weaken the stack guard. > > > [...] > > > > > This *doesn't* fix the LibreOffice regression on i386. > > > > Are there any details about this regression? > > Here: > https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=865303#170 > > I haven't reproduced it in Writer, but if I use Base to create a new > HSQLDB database it reliably crashes (HSQLDB is implemented in Java). I haven't read through previous 169 comments but I do not see any stack trace. Ideally with info proc mapping that would tell us the memory layout. -- Michal Hocko SUSE Labs