Re: [PATCH v12 2/6] x86/entry: Add STACKLEAK erasing the kernel stack at the end of syscalls

From: Alexander Popov <alex.popov@linux.com>
To: Ingo Molnar <mingo@kernel.org>, Kees Cook <keescook@chromium.org>
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Subject: Re: [PATCH v12 2/6] x86/entry: Add STACKLEAK erasing the kernel stack at the end of syscalls
Date: Tue, 22 May 2018 13:58:59 +0300	[thread overview]
Message-ID: <23369d86-ad31-e7c5-e42f-28e0e51ec128@linux.com> (raw)
In-Reply-To: <20180518065349.GA10080@gmail.com>

Hello Ingo and Kees,

On 18.05.2018 09:53, Ingo Molnar wrote:
> * Alexander Popov <alex.popov@linux.com> wrote:
>> --- a/arch/x86/kernel/process_32.c
>> +++ b/arch/x86/kernel/process_32.c
>> @@ -136,6 +136,11 @@ int copy_thread_tls(unsigned long clone_flags, unsigned long sp,
>>  	p->thread.sp0 = (unsigned long) (childregs+1);
>>  	memset(p->thread.ptrace_bps, 0, sizeof(p->thread.ptrace_bps));
>>  
>> +#ifdef CONFIG_GCC_PLUGIN_STACKLEAK
>> +	p->thread.lowest_stack.val = (unsigned long)end_of_stack(p) +
>> +						sizeof(unsigned long);
>> +#endif
> 
> This should use an inline helper:
> 
> 	stackleak_task_init(p);

Right now I can't define such a helper because 'lowest_stack' is a part of
'thread_struct', but arch/x86/include/asm/processor.h and include/linux/sched.h
are independent.

I think the best solution is to move 'lowest_stack' variable to 'task_struct'.

Is there any reason to fold this variable into a 'stackleak_info' structure? I
see everybody happily uses #ifdef in 'task_struct'.

May I define STACKLEAK_POISON and STACKLEAK_POISON_CHECK_DEPTH in sched.h as well?

Looking forward to your reply.
Best regards,
Alexander