linux-kernel - Re: [PATCH v1] mm: abstract shadow stack vma behind arch_is_shadow_stack

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Date: Tue, 2 Jan 2024 15:56:35 +0200
From: Mike Rapoport <rppt@...nel.org>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: Deepak Gupta <debug@...osinc.com>, rick.p.edgecombe@...el.com,
	broonie@...nel.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1] mm: abstract shadow stack vma behind
 arch_is_shadow_stack_vma

On Wed, Dec 27, 2023 at 01:45:14PM -0800, Andrew Morton wrote:
> On Fri, 22 Dec 2023 15:51:04 -0800 Deepak Gupta <debug@...osinc.com> wrote:
> 
> > x86 has used VM_SHADOW_STACK (alias to VM_HIGH_ARCH_5) to encode shadow
> > stack VMA. VM_SHADOW_STACK is thus not possible on 32bit. Some arches may
> > need a way to encode shadow stack on 32bit and 64bit both and they may
> > encode this information differently in VMAs.
> 
> Is such a patch in the pipeline?  Otherwise we're making a change that
> serves no purpose.
> 
> > This patch changes checks of VM_SHADOW_STACK flag in generic code to call
> > to a function `arch_is_shadow_stack_vma` which will return true if arch
> > supports shadow stack and vma is shadow stack else stub returns false.
> > 
> > ...
> >
> > --- a/include/linux/mm.h
> > +++ b/include/linux/mm.h
> > @@ -352,8 +352,21 @@ extern unsigned int kobjsize(const void *objp);
> >   * for more details on the guard size.
> >   */
> >  # define VM_SHADOW_STACK	VM_HIGH_ARCH_5
> > +
> > +static inline bool arch_is_shadow_stack_vma(vm_flags_t vm_flags)
> > +{
> > +	return (vm_flags & VM_SHADOW_STACK) ? true : false;
> > +}
> 
> The naming seems a little wrong.  I'd expect it to take a vma* arg. 
> Maybe just drop the "_vma"?

I'd suggest to use vma_is_shadow_stack() to make it inline with other
vma_is_*() tests.

-- 
Sincerely yours,
Mike.