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Date: Tue, 26 Jun 2018 17:55:40 -0700
From: Laura Abbott <labbott@...hat.com>
To: Kees Cook <keescook@...omium.org>
Cc: Alexander Popov <alex.popov@...ux.com>,
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 LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v13 (resend) 2/6] x86/entry: Add STACKLEAK erasing the
 kernel stack at the end of syscalls

On 06/26/2018 05:21 PM, Kees Cook wrote:
> On Tue, Jun 26, 2018 at 5:13 PM, Kees Cook <keescook@...omium.org> wrote:
>> The only arch-specific part is current_top_of_stack(), so it seems
>> like just solving current_top_of_stack() and copying on_thread_stack()
>> directly should work, yes? I would think sticking those directly into
>> asm/processor.h on arm64 would be okay?
> 
> The difference in the earlier x86 and arm64 erase_kstack was:
> 
> x86:
>          if (on_thread_stack())
>                  boundary = current_stack_pointer;
>          else
>                  boundary = current_top_of_stack();
> 
> arm64:
>          boundary = current_stack_pointer;
> 
> If a sane current_top_of_stack() isn't possible on arm64, I'm not
> opposed to a small bit of arch-specific ifdef in there:
> 
>          boundary = get_stack_boundary();
> 
> static inline unsigned long get_stack_boundary(void)
> {
> #ifdef CONFIG_X86
>          if (!on_thread_stack())
>                  return current_top_of_stack();
> #else
>           return current_stack_pointer;
> }
> 
> -Kees
> 

I _think_ I have reasonable implementations for both functions,
I was asking about pulling stuff out into a new header because
I wanted to see about reusing on_task_stack which was defined
in asm/stacktrace.h and I was concerned about include nightmares
with asm/processor.h . I'll see what I come up with.

Thanks,
Laura

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