linux-kernel - Re: [PATCH] NX protection for kernel data : fix 32 bits S3 suspend

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Date:	Tue, 01 Feb 2011 14:25:32 +0100
From:	castet.matthieu@...e.fr
To:	Ingo Molnar <mingo@...e.hu>
Cc:	matthieu castet <castet.matthieu@...e.fr>,
	Linux Kernel list <linux-kernel@...r.kernel.org>,
	linux-security-module@...r.kernel.org,
	Matthias Hopf <mhopf@...e.de>, rjw@...k.pl,
	Andrew Morton <akpm@...ux-foundation.org>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH] NX protection for kernel data : fix 32 bits S3 suspend

Quoting Ingo Molnar <mingo@...e.hu>:

>
> * matthieu castet <castet.matthieu@...e.fr> wrote:
>
> >  static inline int is_kernel_text(unsigned long addr)
> >  {
> > +#if defined(CONFIG_X86_32) && defined(CONFIG_ACPI_SLEEP)
> > +	/*
> > +	 * We need to make the wakeup trampoline in first 1MB !NX
> > +	 */
> > +	if (addr >= PAGE_OFFSET && addr <= (PAGE_OFFSET + (1<<20)))
> > +		return 1;
> > +#endif
>
> That's pretty ugly. Why not use set_memory_x()/set_memory_nx(), and only for
> the
> trampoline itself? Does the whole 1MB need to be marked X?
The previous code was doing that.

If you prefer I can revert to the old code :

static inline int is_kernel_text(unsigned long addr)
{
    if (addr >= PAGE_OFFSET && addr <= (unsigned long)__init_end)
        return 1;
    return 0;
}

The proper fix will be done in 2.6.29, when S3 resume 32 bit trampoline will be
merged with 64 bit (ie call smp trampoline) [1]

>
> Same goes for the Xen fix.
>
The Xen fix reverts code to old behavior.
We can't assume that all data/bss will be RW. And I see no way to detect witch
page in data/bss we should not force to RW in static protection.
So we assume the code that change protection of data/bss knows what it is doing
(that what was doing old code).

Matthieu


[1]http://marc.info/?l=linux-kernel&m=129616541603610&w=2
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