Messages in this thread | | | Subject | Re: [PATCH] mm: larger stack guard gap, between vmas | From | Ximin Luo <> | Date | Tue, 04 Jul 2017 14:19:00 +0000 |
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Michal Hocko: > 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. >
I've written up an explanation of what happens in the Rust case here:
https://github.com/rust-lang/rust/issues/43052
Hopefully I got the details about Linux correct - I only had them explained to me last night - please reply on that page if not.
X
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