kernel-hardening - Re: [PATCH 2/2] x86/modules: Make x86 allocs to flush when free

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Date: Thu, 29 Nov 2018 00:02:15 +0000
From: "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
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	<netdev@...r.kernel.org>, "Hansen, Dave" <dave.hansen@...el.com>
Subject: Re: [PATCH 2/2] x86/modules: Make x86 allocs to flush when free

On Wed, 2018-11-28 at 15:11 -0800, Andrew Morton wrote:
> On Tue, 27 Nov 2018 16:07:54 -0800 Rick Edgecombe <rick.p.edgecombe@...el.com>
> wrote:
> 
> > Change the module allocations to flush before freeing the pages.
> > 
> > ...
> > 
> > --- a/arch/x86/kernel/module.c
> > +++ b/arch/x86/kernel/module.c
> > @@ -87,8 +87,8 @@ void *module_alloc(unsigned long size)
> >  	p = __vmalloc_node_range(size, MODULE_ALIGN,
> >  				    MODULES_VADDR + get_module_load_offset(),
> >  				    MODULES_END, GFP_KERNEL,
> > -				    PAGE_KERNEL_EXEC, 0, NUMA_NO_NODE,
> > -				    __builtin_return_address(0));
> > +				    PAGE_KERNEL_EXEC, VM_IMMEDIATE_UNMAP,
> > +				    NUMA_NO_NODE, __builtin_return_address(0));
> >  	if (p && (kasan_module_alloc(p, size) < 0)) {
> >  		vfree(p);
> >  		return NULL;
> 
> Should any other architectures do this?

I would think everything that has something like an NX bit and doesn't use the
default module_alloc implementation.

I could add the flag for every arch that defines PAGE_KERNEL_EXEC, but I don't
have a good way to test on all of those architectures.

Thanks,

Rick

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