Messages in this thread | | | Subject | Re: [PATCH] mm: larger stack guard gap, between vmas | From | Ben Hutchings <> | Date | Tue, 04 Jul 2017 13:21:02 +0100 |
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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.
> 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).
Ben.
-- Ben Hutchings The world is coming to an end. Please log off. [unhandled content-type:application/pgp-signature] | |