Re: [Xen-devel] pv-grub will cause page fault if build with flag -fstack-protector

[Samuel Thibault <samuel.thibault@xxxxxxxxxxxx>]

Ian Campbell, le Tue 16 Apr 2013 10:47:18 +0100, a écrit :
> On Tue, 2013-04-16 at 10:34 +0100, Chunyan Liu wrote:
> > We asked for Jan's opinion whether we can remove the flag or there
> > isn't a problem with stubdom overwriting something on the stack . Jan
> > viewed it as a mistake use of flag:
> > > I generally view it as a mistake enforce certain kinds of
> > (intrusive) flags onto builds of code that may assume to have full
> > control of everything (e.g. kernel like, which stubdom clearly is).
> > 
> > I wonder if there is other opinion?
> 
> I agree with Jan.

mini-os, which stubdoms are based on, explicitly tries to disable
stack-protector, see extras/mini-os/minios.mk

> > I checked the objdump of problem pv-grub, the page fault place is in
> > xc_interface_open_common, the detail line is a line inserted by
> > -fstack-protector (see 0x404bb in following):
> 
> If you wanted to get really advanced you could implement stack protector
> support for mini-os. I've no idea how hard that would be though.

Actually we can't really support it, because the code introduced by
gcc, which typically uses fs: or gs: adressing, is host-dependent, i.e.
depending on being built on linux, or on freebsd, etc. mini-os would
have to behave differently because the code introduced by gcc behaves
differently... The solution would be to use a separate host triplet, but
we ended up avoiding doing it due to the introduced complexity.

Samuel

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