linux-kernel - Re: [PATCH v2 2/2] arm64: scs: use vmapped IRQ and SDEI shadow stacks

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Date:   Tue, 1 Dec 2020 10:26:36 +0000
From:   Will Deacon <will@...nel.org>
To:     Sami Tolvanen <samitolvanen@...gle.com>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Mark Rutland <mark.rutland@....com>,
        James Morse <james.morse@....com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Kees Cook <keescook@...omium.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 2/2] arm64: scs: use vmapped IRQ and SDEI shadow stacks

On Tue, Dec 01, 2020 at 10:18:19AM +0000, Will Deacon wrote:
> On Mon, Nov 30, 2020 at 01:13:07PM -0800, Sami Tolvanen wrote:
> > On Mon, Nov 30, 2020 at 3:49 AM Will Deacon <will@...nel.org> wrote:
> > > On Tue, Nov 24, 2020 at 11:59:40AM -0800, Sami Tolvanen wrote:
> > > >       for_each_possible_cpu(cpu) {
> > > > -             err = _init_sdei_stack(&sdei_stack_normal_ptr, cpu);
> > > > -             if (err)
> > > > -                     break;
> > > > -             err = _init_sdei_stack(&sdei_stack_critical_ptr, cpu);
> > > > -             if (err)
> > > > -                     break;
> > > > +             if (IS_ENABLED(CONFIG_VMAP_STACK)) {
> > > > +                     err = _init_sdei_stack(&sdei_stack_normal_ptr, cpu);
> > > > +                     if (err)
> > > > +                             break;
> > > > +                     err = _init_sdei_stack(&sdei_stack_critical_ptr, cpu);
> > > > +                     if (err)
> > > > +                             break;
> > > > +             }
> > > > +             if (IS_ENABLED(CONFIG_SHADOW_CALL_STACK)) {
> > > > +                     err = _init_sdei_scs(&sdei_shadow_call_stack_normal_ptr, cpu);
> > > > +                     if (err)
> > > > +                             break;
> > > > +                     err = _init_sdei_scs(&sdei_shadow_call_stack_critical_ptr, cpu);
> > > > +                     if (err)
> > > > +                             break;
> > >
> > > This looks ok to me, but I think it would be better to follow the same
> > > approach as you have for the IRQ stacks and instead have a separate
> > > init_sdei_scs() function (similarly for the free() path), which means
> > > you can simply the IS_ENABLED() checks too.
> > 
> > OK, I can change this in v3. It makes error handling in
> > sdei_arch_get_entry_point() a bit more awkward though. We'll need
> > something like this:
> > 
> >         if (IS_ENABLED(CONFIG_VMAP_STACK)) {
> >                 if (init_sdei_stacks())
> >                         return 0;
> >         }
> > 
> >         if (IS_ENABLED(CONFIG_SHADOW_CALL_STACK)) {
> >                 if (init_sdei_scs()) {
> >                         if (IS_ENABLED(CONFIG_VMAP_STACK))
> >                                 free_sdei_stacks();
> >                         return 0;
> >                 }
> 
> Can you push the IS_ENABLED() checks into their respective functions?
> Then you can do something like:
> 
> 	if (init_sdei_stacks())
> 		return 0;
> 
> 	if (init_sdei_scs())
> 		goto out_free_stacks;
> 
> 	...
> 
> out_free_stacks:
> 	free_sdei_stacks();
> 	return 0;

Wait, I see you already posted a v3. Maybe I can just hack this up on top...

Will