linux-kernel - Re: [PATCH 6/6] scs: Move DEFINE

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Date:   Mon, 18 May 2020 13:14:41 +0100
From:   Mark Rutland <mark.rutland@....com>
To:     Will Deacon <will@...nel.org>
Cc:     linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        Sami Tolvanen <samitolvanen@...gle.com>,
        Kees Cook <keescook@...omium.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Mark Rutland <mark.rutland@...com>,
        Jann Horn <jannh@...gle.com>, Ard Biesheuvel <ardb@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>, kernel-team@...roid.com
Subject: Re: [PATCH 6/6] scs: Move DEFINE_SCS macro into core code

On Fri, May 15, 2020 at 06:27:56PM +0100, Will Deacon wrote:
> Defining static shadow call stacks is not architecture-specific, so move
> the DEFINE_SCS() macro into the core header file.
> 
> Signed-off-by: Will Deacon <will@...nel.org>

I think that we'll have to pull this back into arch code if/when we deal
with VMAP'd stacks, so I'm not sure this is worthwhile given the
diffstat is balanced.

Mark.

> ---
>  arch/arm64/kernel/scs.c | 4 ----
>  include/linux/scs.h     | 4 ++++
>  2 files changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/arm64/kernel/scs.c b/arch/arm64/kernel/scs.c
> index 955875dff9e1..e8f7ff45dd8f 100644
> --- a/arch/arm64/kernel/scs.c
> +++ b/arch/arm64/kernel/scs.c
> @@ -8,10 +8,6 @@
>  #include <linux/percpu.h>
>  #include <linux/scs.h>
>  
> -/* Allocate a static per-CPU shadow stack */
> -#define DEFINE_SCS(name)						\
> -	DEFINE_PER_CPU(unsigned long [SCS_SIZE/sizeof(long)], name)	\
> -
>  DEFINE_SCS(irq_shadow_call_stack);
>  
>  #ifdef CONFIG_ARM_SDE_INTERFACE
> diff --git a/include/linux/scs.h b/include/linux/scs.h
> index 2fd3df50e93e..6dec390cf154 100644
> --- a/include/linux/scs.h
> +++ b/include/linux/scs.h
> @@ -26,6 +26,10 @@
>  /* An illegal pointer value to mark the end of the shadow stack. */
>  #define SCS_END_MAGIC		(0x5f6UL + POISON_POINTER_DELTA)
>  
> +/* Allocate a static per-CPU shadow stack */
> +#define DEFINE_SCS(name)						\
> +	DEFINE_PER_CPU(unsigned long [SCS_SIZE/sizeof(long)], name)	\
> +
>  #define task_scs(tsk)		(task_thread_info(tsk)->scs_base)
>  #define task_scs_sp(tsk)	(task_thread_info(tsk)->scs_sp)
>  
> -- 
> 2.26.2.761.g0e0b3e54be-goog
>