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

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Message-ID: <CABCJKud6UiidpqqwJcghnqLKDkqM3pzMUUwe3_HH3ODDqOdANA@mail.gmail.com>
Date:   Mon, 30 Nov 2020 13:13:07 -0800
From:   Sami Tolvanen <samitolvanen@...gle.com>
To:     Will Deacon <will@...nel.org>
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 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:
> > Use scs_alloc() to allocate also IRQ and SDEI shadow stacks instead of
> > using statically allocated stacks.
> >
> > Signed-off-by: Sami Tolvanen <samitolvanen@...gle.com>
> > ---
> >  arch/arm64/kernel/Makefile |  1 -
> >  arch/arm64/kernel/entry.S  |  6 ++--
> >  arch/arm64/kernel/irq.c    | 19 ++++++++++
> >  arch/arm64/kernel/scs.c    | 16 ---------
> >  arch/arm64/kernel/sdei.c   | 71 +++++++++++++++++++++++++++++++-------
> >  include/linux/scs.h        |  4 ---
> >  6 files changed, 81 insertions(+), 36 deletions(-)
> >  delete mode 100644 arch/arm64/kernel/scs.c
>
> [...]
>
> > @@ -70,18 +97,40 @@ static int _init_sdei_stack(unsigned long * __percpu *ptr, int cpu)
> >       return 0;
> >  }
> >
> > +static int _init_sdei_scs(unsigned long * __percpu *ptr, int cpu)
> > +{
> > +     void *s;
> > +
> > +     s = scs_alloc(cpu_to_node(cpu));
> > +     if (!s)
> > +             return -ENOMEM;
> > +     per_cpu(*ptr, cpu) = s;
> > +
> > +     return 0;
> > +}
> > +
> >  static int init_sdei_stacks(void)
> >  {
> >       int cpu;
> >       int err = 0;
> >
> >       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;
                }
        }

Sami