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Date: Tue, 22 May 2018 13:58:59 +0300
From: Alexander Popov <alex.popov@...ux.com>
To: Ingo Molnar <mingo@...nel.org>, Kees Cook <keescook@...omium.org>
Cc: kernel-hardening@...ts.openwall.com, PaX Team <pageexec@...email.hu>,
 Brad Spengler <spender@...ecurity.net>, Andy Lutomirski <luto@...nel.org>,
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 Mark Rutland <mark.rutland@....com>,
 Ard Biesheuvel <ard.biesheuvel@...aro.org>, Borislav Petkov <bp@...en8.de>,
 Richard Sandiford <richard.sandiford@....com>,
 Thomas Gleixner <tglx@...utronix.de>, "H . Peter Anvin" <hpa@...or.com>,
 Peter Zijlstra <a.p.zijlstra@...llo.nl>, "Dmitry V . Levin"
 <ldv@...linux.org>, Emese Revfy <re.emese@...il.com>,
 Jonathan Corbet <corbet@....net>, Andrey Ryabinin <aryabinin@...tuozzo.com>,
 "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
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 <dwmw@...zon.co.uk>, Josh Poimboeuf <jpoimboe@...hat.com>,
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 <me@...ehuey.com>, Dmitry Safonov <dsafonov@...tuozzo.com>,
 Will Deacon <will.deacon@....com>, Arnd Bergmann <arnd@...db.de>,
 Florian Weimer <fweimer@...hat.com>,
 Boris Lukashev <blukashev@...pervictus.com>,
 Andrey Konovalov <andreyknvl@...gle.com>, x86@...nel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v12 2/6] x86/entry: Add STACKLEAK erasing the kernel stack
 at the end of syscalls

Hello Ingo and Kees,

On 18.05.2018 09:53, Ingo Molnar wrote:
> * Alexander Popov <alex.popov@...ux.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

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