Re: [PATCH 05/13] clocksource/arm_arch_timer: Fix MMIO base address vs callback ordering issue

[Oliver Upton]

On Mon, Aug 9, 2021 at 8:27 AM Marc Zyngier <maz@xxxxxxxxxx> wrote:
>
> The MMIO timer base address gets published after we have registered
> the callbacks and the interrupt handler, which is... a bit dangerous.
>
> Fix this by moving the base address publication to the point where
> we register the timer, and expose a pointer to the timer structure
> itself rather than a naked value.
>
> Signed-off-by: Marc Zyngier <maz@xxxxxxxxxx>

Is this patch stable-worthy? I take it there haven't been any reports
of issues, though this seems rather perilous.

Reviewed-by: Oliver Upton <oupton@xxxxxxxxxx>

> ---
>  drivers/clocksource/arm_arch_timer.c | 27 +++++++++++++--------------
>  1 file changed, 13 insertions(+), 14 deletions(-)
>
> diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c
> index 160464f75017..ca7761d8459a 100644
> --- a/drivers/clocksource/arm_arch_timer.c
> +++ b/drivers/clocksource/arm_arch_timer.c
> @@ -54,13 +54,13 @@
>
>  static unsigned arch_timers_present __initdata;
>
> -static void __iomem *arch_counter_base __ro_after_init;
> -
>  struct arch_timer {
>         void __iomem *base;
>         struct clock_event_device evt;
>  };
>
> +static struct arch_timer *arch_timer_mem __ro_after_init;
> +
>  #define to_arch_timer(e) container_of(e, struct arch_timer, evt)
>
>  static u32 arch_timer_rate __ro_after_init;
> @@ -975,9 +975,9 @@ static u64 arch_counter_get_cntvct_mem(void)
>         u32 vct_lo, vct_hi, tmp_hi;
>
>         do {
> -               vct_hi = readl_relaxed(arch_counter_base + CNTVCT_HI);
> -               vct_lo = readl_relaxed(arch_counter_base + CNTVCT_LO);
> -               tmp_hi = readl_relaxed(arch_counter_base + CNTVCT_HI);
> +               vct_hi = readl_relaxed(arch_timer_mem->base + CNTVCT_HI);
> +               vct_lo = readl_relaxed(arch_timer_mem->base + CNTVCT_LO);
> +               tmp_hi = readl_relaxed(arch_timer_mem->base + CNTVCT_HI);
>         } while (vct_hi != tmp_hi);
>
>         return ((u64) vct_hi << 32) | vct_lo;
> @@ -1168,25 +1168,25 @@ static int __init arch_timer_mem_register(void __iomem *base, unsigned int irq)
>  {
>         int ret;
>         irq_handler_t func;
> -       struct arch_timer *t;
>
> -       t = kzalloc(sizeof(*t), GFP_KERNEL);
> -       if (!t)
> +       arch_timer_mem = kzalloc(sizeof(*arch_timer_mem), GFP_KERNEL);
> +       if (!arch_timer_mem)
>                 return -ENOMEM;
>
> -       t->base = base;
> -       t->evt.irq = irq;
> -       __arch_timer_setup(ARCH_TIMER_TYPE_MEM, &t->evt);
> +       arch_timer_mem->base = base;
> +       arch_timer_mem->evt.irq = irq;
> +       __arch_timer_setup(ARCH_TIMER_TYPE_MEM, &arch_timer_mem->evt);
>
>         if (arch_timer_mem_use_virtual)
>                 func = arch_timer_handler_virt_mem;
>         else
>                 func = arch_timer_handler_phys_mem;
>
> -       ret = request_irq(irq, func, IRQF_TIMER, "arch_mem_timer", &t->evt);
> +       ret = request_irq(irq, func, IRQF_TIMER, "arch_mem_timer", &arch_timer_mem->evt);
>         if (ret) {
>                 pr_err("Failed to request mem timer irq\n");
> -               kfree(t);
> +               kfree(arch_timer_mem);
> +               arch_timer_mem = NULL;
>         }
>
>         return ret;
> @@ -1444,7 +1444,6 @@ arch_timer_mem_frame_register(struct arch_timer_mem_frame *frame)
>                 return ret;
>         }
>
> -       arch_counter_base = base;
>         arch_timers_present |= ARCH_TIMER_TYPE_MEM;
>
>         return 0;
> --
> 2.30.2
>