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

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Date:	Thu, 03 Feb 2011 14:11:01 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Ingo Molnar <mingo@...e.hu>
CC:	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>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] NX protection for kernel data : fix 32 bits S3 suspend

On 02/01/2011 10:26 PM, Ingo Molnar wrote:
> 
> * castet.matthieu@...e.fr <castet.matthieu@...e.fr> wrote:
> 
>> 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.
> 
> So why not call set_memory_x() in your patch? Mind trying that?
> 

OK, there seems to be considerable duplication between
static_protections() and local invocation.  Consider PCI BIOS, which is
another X-needed region.

In static_protections() we have:

>         /*
>          * The BIOS area between 640k and 1Mb needs to be executable for
>          * PCI BIOS based config access (CONFIG_PCI_GOBIOS) support.
>          */
> #ifdef CONFIG_PCI_BIOS
>         if (pcibios_enabled && within(pfn, BIOS_BEGIN >> PAGE_SHIFT, BIOS_END >> PAGE_SHIFT))
>                 pgprot_val(forbidden) |= _PAGE_NX;
> #endif

... however, in arch/x86/pci/pcbios.c:

> static inline void set_bios_x(void)
> {
>         pcibios_enabled = 1;
>         set_memory_x(PAGE_OFFSET + BIOS_BEGIN, (BIOS_END - BIOS_BEGIN) >> PAGE_SHIFT);
>         if (__supported_pte_mask & _PAGE_NX)
>                 printk(KERN_INFO "PCI : PCI BIOS aera is rw and x. Use pci=nobios if you want it NX.\n");
> }

This is blatant and insanely ugly code duplication!  In particular,
static_protections() is "action at a distance" which has no business
existing at all.

What I want to know is if static_protections() can somehow override
set_bios_x() in this context (in which case it's a serious design
error), or if it is plain redundant -- in the latter case we should
simply use the same technique elsewhere.

	-hpa
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