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

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Message-ID: <20080301094525.GQ17932@hjernemadsen.org>
Date:	Sat, 1 Mar 2008 10:45:25 +0100
From:	"Klaus S. Madsen" <ksm@...rnemadsen.org>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	LKML <linux-kernel@...r.kernel.org>, Pavel Machek <pavel@....cz>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: Regression in 2.6.25-rc3: s2ram segfaults before suspending

On Fri, Feb 29, 2008 at 22:26:54 +0100, Ingo Molnar wrote:
> 
> * H. Peter Anvin <hpa@...or.com> 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?

-- 
Kind regards
	Klaus S. Madsen

View attachment "config.t61p.txt" of type "text/plain" (50563 bytes)