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

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Date: Tue, 2 Jan 2024 10:45:36 -0800
From: Deepak Gupta <debug@...osinc.com>
To: Mike Rapoport <rppt@...nel.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>, 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 Tue, Jan 2, 2024 at 5:57 AM Mike Rapoport <rppt@...nel.org> wrote:
>
> 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.

Noted. Thanks

>
> --
> Sincerely yours,
> Mike.