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

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Message-ID: <20201130114940.GB24563@willie-the-truck>
Date:   Mon, 30 Nov 2020 11:49:40 +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@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/2] arm64: scs: use vmapped IRQ and SDEI shadow stacks

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.

Either way:

Acked-by: Will Deacon <will@...nel.org>

Will