Re: [announce] [patch] NX (No eXecute) support for x86, 2.6.7-rc2-bk2

[Jeff Garzik <jgarzik@pobox.com>]

Rusty Russell wrote:
> On Thu, 2004-06-03 at 06:50, Ingo Molnar wrote:
> 
>>furthermore, the patch also implements 'NX protection' for kernelspace
>>code: only the kernel code and modules are executable - so even
> 
> 
> No, actually, it doesn't quite do that:
> 
> --- linux/kernel/module.c.orig	
> +++ linux/kernel/module.c	
> @@ -1431,7 +1431,7 @@ static struct module *load_module(void _
>  
>  	/* Suck in entire file: we'll want most of it. */
>  	/* vmalloc barfs on "unusual" numbers.  Check here */
> -	if (len > 64 * 1024 * 1024 || (hdr = vmalloc(len)) == NULL)
> +	if (len > 64 * 1024 * 1024 || (hdr = vmalloc_exec(len)) == NULL)
>  		return ERR_PTR(-ENOMEM);
>  	if (copy_from_user(hdr, umod, len) != 0) {
>  		err = -EFAULT;
> 
> This is where we such the module file into kernel memory to parse it,
> not where we actually copy the memory.
> 
> You want to replace the arch-specific module_alloc() function for this.
> Or even better, reset the NX bit only on executable sections (in the
> arch-specific module_finalize(), using mod->core_text_size and
> mod->init_text_size).  No generic changes necessary.
> 
> What surprises me is that this error didn't cause your kernel to explode
> the moment you inserted a module containing a function...


bah, modules are for lame people who don't want to squeeze that last 
%0.00001 of additional performance out of their kernel by reducing TLB 
and I-cache misses...

	Jeff