From mboxrd@z Thu Jan  1 00:00:00 1970
Subject: Re: [PATCH v12 2/6] x86/entry: Add STACKLEAK erasing the kernel stack
 at the end of syscalls
References: <1526488097-20611-1-git-send-email-alex.popov@linux.com>
 <1526488097-20611-3-git-send-email-alex.popov@linux.com>
 <20180518065349.GA10080@gmail.com>
From: Alexander Popov <alex.popov@linux.com>
Message-ID: <23369d86-ad31-e7c5-e42f-28e0e51ec128@linux.com>
Date: Tue, 22 May 2018 13:58:59 +0300
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To: Ingo Molnar <mingo@kernel.org>, Kees Cook <keescook@chromium.org>
Cc: kernel-hardening@lists.openwall.com, PaX Team <pageexec@freemail.hu>, Brad Spengler <spender@grsecurity.net>, Andy Lutomirski <luto@kernel.org>, Tycho Andersen <tycho@tycho.ws>, Laura Abbott <labbott@redhat.com>, Mark Rutland <mark.rutland@arm.com>, Ard Biesheuvel <ard.biesheuvel@linaro.org>, Borislav Petkov <bp@alien8.de>, Richard Sandiford <richard.sandiford@arm.com>, Thomas Gleixner <tglx@linutronix.de>, "H . Peter Anvin" <hpa@zytor.com>, Peter Zijlstra <a.p.zijlstra@chello.nl>, "Dmitry V . Levin" <ldv@altlinux.org>, Emese Revfy <re.emese@gmail.com>, Jonathan Corbet <corbet@lwn.net>, Andrey Ryabinin <aryabinin@virtuozzo.com>, "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>, Thomas Garnier <thgarnie@google.com>, Andrew Morton <akpm@linux-foundation.org>, Alexei Starovoitov <ast@kernel.org>, Josef Bacik <jbacik@fb.com>, Masami Hiramatsu <mhiramat@kernel.org>, Nicholas Piggin <npiggin@gmail.com>, Al Viro <viro@zeniv.linux.org.uk>, "David S . Miller" <davem@davemloft.net>, Ding Tianhong <dingtianhong@huawei.com>, David Woodhouse <dwmw@amazon.co.uk>, Josh Poimboeuf <jpoimboe@redhat.com>, Steven Rostedt <rostedt@goodmis.org>, Dominik Brodowski <linux@dominikbrodowski.net>, Juergen Gross <jgross@suse.com>, Linus Torvalds <torvalds@linux-foundation.org>, Greg Kroah-Hartman <gregkh@linuxfoundation.org>, Dan Williams <dan.j.williams@intel.com>, Dave Hansen <dave.hansen@linux.intel.com>, Mathias Krause <minipli@googlemail.com>, Vikas Shivappa <vikas.shivappa@linux.intel.com>, Kyle Huey <me@kylehuey.com>, Dmitry Safonov <dsafonov@virtuozzo.com>, Will Deacon <will.deacon@arm.com>, Arnd Bergmann <arnd@arndb.de>, Florian Weimer <fweimer@redhat.com>, Boris Lukashev <blukashev@sempervictus.com>, Andrey Konovalov <andreyknvl@google.com>, x86@kernel.org, linux-kernel@vger.kernel.org
List-ID: <kernel-hardening.lists.openwall.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