Re: [PATCH 11/17] stackleak: allow C to call stackleak_erase()

From: Anshuman Khandual <anshuman.khandual@arm.com>
To: Mark Rutland <mark.rutland@arm.com>,
	linux-arm-kernel@lists.infradead.org, catalin.marinas@arm.com,
	will@kernel.org, james.morse@arm.com
Cc: keescook@chromium.org, maz@kernel.org, broonie@kernel.org,
	labbott@redhat.com, robin.murphy@arm.com,
	julien.thierry.kdev@gmail.com, alex.popov@linux.com
Subject: Re: [PATCH 11/17] stackleak: allow C to call stackleak_erase()
Date: Fri, 10 Jan 2020 09:15:31 +0530	[thread overview]
Message-ID: <b7c6d434-16a1-f270-b656-a1814ea6bab3@arm.com> (raw)
In-Reply-To: <20200108185634.1163-12-mark.rutland@arm.com>

On 01/09/2020 12:26 AM, Mark Rutland wrote:
> Currently, stackleak_erase() has no prototype in a header file, and has
> to be called directly from low-level architecture entry assembly code.
> This necessitates ifdeffery and complicates the entry assembly.
> 
> To ameliorate matters, let's provide a prototype so that architecture
> can call stackleak_erase() from slightly higher level C code used as
> part of the entry flow. This makes things easier to read and maintain.

Does this need to be a separate patch or should it be folded into
"[PATCH 13/17] arm64: entry: move common el0 entry/return work to C"
which actually adds the first C call site for this function.

> 
> Signed-off-by: Mark Rutland <mark.rutland@arm.com>
> Cc: Alexander Popov <alex.popov@linux.com>
> Cc: Catalin Marinas <catalin.marinas@arm.com>
> Cc: Kees Cook <keescook@chromium.org>
> Cc: Laura Abbott <labbott@redhat.com>
> Cc: Will Deacon <will@kernel.org>
> ---
>  include/linux/stackleak.h | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/include/linux/stackleak.h b/include/linux/stackleak.h
> index 3d5c3271a9a8..2b09d3759c76 100644
> --- a/include/linux/stackleak.h
> +++ b/include/linux/stackleak.h
> @@ -15,6 +15,8 @@
>  #ifdef CONFIG_GCC_PLUGIN_STACKLEAK
>  #include <asm/stacktrace.h>
>  
> +asmlinkage void notrace stackleak_erase(void);
> +
>  static inline void stackleak_task_init(struct task_struct *t)
>  {
>  	t->lowest_stack = (unsigned long)end_of_stack(t) + sizeof(unsigned long);
> @@ -30,6 +32,7 @@ int stack_erasing_sysctl(struct ctl_table *table, int write,
>  
>  #else /* !CONFIG_GCC_PLUGIN_STACKLEAK */
>  static inline void stackleak_task_init(struct task_struct *t) { }
> +static inline void stackleak_erase(void) { }
>  #endif
>  
>  #endif
> 

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