linux-hardening - Re: [PATCH v5 24/32] ARM: run softirqs on the per-CPU IRQ stack

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Message-ID: <CAMj1kXHJRo1U5Nmw0arB9HNuso=eWfEmsVN6bZagmx-UUYs=dQ@mail.gmail.com>
Date:   Tue, 22 Mar 2022 10:35:18 +0100
From:   Ard Biesheuvel <ardb@...nel.org>
To:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:     Russell King <linux@...linux.org.uk>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        linux-hardening@...r.kernel.org, Nicolas Pitre <nico@...xnic.net>,
        Arnd Bergmann <arnd@...db.de>,
        Kees Cook <keescook@...omium.org>,
        Keith Packard <keithpac@...zon.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Tony Lindgren <tony@...mide.com>,
        Marc Zyngier <maz@...nel.org>,
        Vladimir Murzin <vladimir.murzin@....com>,
        Jesse Taube <mr.bossman075@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH v5 24/32] ARM: run softirqs on the per-CPU IRQ stack

On Tue, 22 Mar 2022 at 10:04, Sebastian Andrzej Siewior
<bigeasy@...utronix.de> wrote:
>
> On 2022-01-24 18:47:36 [+0100], Ard Biesheuvel wrote:
> > @@ -58,6 +61,17 @@ static void __init init_irq_stacks(void)
> >       }
> >  }
> >
> > +static void ____do_softirq(void *arg)
> > +{
> > +     __do_softirq();
> > +}
> > +
> > +void do_softirq_own_stack(void)
> > +{
> > +     call_with_stack(____do_softirq, NULL,
> > +                     __this_cpu_read(irq_stack_ptr));
> > +}
> > +
>
> Do I miss the obvious here or is the irq_stack_ptr only used for
> softirqs and not for hardirqs?
>
> >  int arch_show_interrupts(struct seq_file *p, int prec)
> >  {
> >  #ifdef CONFIG_FIQ
>

It is also used for hard IRQs - please refer to the irq_handler macro
in arch/arm/kernel/entry-armv.S