Re: Regression in 2.6.25-rc3: s2ram segfaults before suspending

[H. Peter Anvin]

Klaus S. Madsen wrote:
> On Fri, Feb 29, 2008 at 22:26:54 +0100, Ingo Molnar wrote:
> > * H. Peter Anvin <hpa@xxxxxxxxx> wrote:
> >
> > > Klaus S. Madsen wrote:
> > > > open("/dev/mem", O_RDWR)                = 5
> > > > mmap2(NULL, 1282, PROT_READ|PROT_WRITE|PROT_EXEC, MAP_SHARED|MAP_FIXED, 5, 0) = 0
> > > > mmap2(0xa0000, 393216, PROT_READ|PROT_WRITE, MAP_SHARED|MAP_FIXED, 5, 0xa0) = 0xa0000
> > >                          ^^^^^^^^^^^^^^^^^^^^
> > > > close(5)                                = 0
> > > > ioperm(0, 0x400, 0x1)                   = 0
> > > > iopl(0x3)                               = 0
> > > > access("/sys/bus/pci", R_OK)            = 0
> > > > write(1, "Calling get_mode\n", 17)      = 17
> > > > vm86(0x1, 0xb7f14ccc, 0xb7f14830, 0xc000, 0x18b6 <unfinished ...>
> > > > --- SIGSEGV (Segmentation fault) @ 0 (0) ---
> > > > +++ killed by SIGSEGV (core dumped) +++
> > > This is the VGA BIOS being mapped, it's mapped PROT_READ|PROT_WRITE, but  
> > > no PROT_EXEC; if the kernel is NX-capable it *should* segfault trying to 
> > > execute out of this area, which is exactly what will happen when vm86 
> > > executes INT 10h.
> > >
> > > If we can find that mmap() in the s2ram source code and add PROT_EXEC 
> > > to it, it would be interesting.
> > Klaus, could you send your .config as well? Lets make sure that NX is 
> > even relevant in this context.
> Allright. The mmap in question is in the x86-common.c file in libx86,
> and adding PROT_EXEC to it solves the problem.
>
> I have attached my .config.
>
> The only thing I don't understand is why this is suddenly a problem with
> 2.6.25, and not with 2.6.24? Is there a bug in 2.6.24 and previously
> that allows real-mode execution of non-executable pages?

One wonders, especially since the checkin it was bisected to it had 
nothing to do with NX.  I suspect there is either a bug in the NX logic, 
which this checkin inadvertently fixed(!), or there is an ad hoc hack 
that should probably never have existed.  More investigation necessary, 
but now we know a lot more.

	-hpa
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