[<prev] [next>] [day] [month] [year] [list]
Message-ID: <bd2c220b-f449-afbb-0b00-a868c8b33afe@linux.com>
Date: Fri, 30 Mar 2018 00:34:21 +0300
From: Alexander Popov <alex.popov@...ux.com>
To: Shivappa Vikas <vikas.shivappa@...ux.intel.com>,
kernel-hardening@...ts.openwall.com, Kees Cook <keescook@...omium.org>,
PaX Team <pageexec@...email.hu>, Brad Spengler <spender@...ecurity.net>,
Ingo Molnar <mingo@...nel.org>, Andy Lutomirski <luto@...nel.org>,
Tycho Andersen <tycho@...ho.ws>, Laura Abbott <labbott@...hat.com>,
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>,
Thomas Garnier <thgarnie@...gle.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Alexei Starovoitov <ast@...nel.org>, Josef Bacik <jbacik@...com>,
Masami Hiramatsu <mhiramat@...nel.org>, Nicholas Piggin <npiggin@...il.com>,
Al Viro <viro@...iv.linux.org.uk>, "David S . Miller" <davem@...emloft.net>,
Ding Tianhong <dingtianhong@...wei.com>, David Woodhouse
<dwmw@...zon.co.uk>, Josh Poimboeuf <jpoimboe@...hat.com>,
Steven Rostedt <rostedt@...dmis.org>,
Dominik Brodowski <linux@...inikbrodowski.net>,
Juergen Gross <jgross@...e.com>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Dan Williams <dan.j.williams@...el.com>,
Dave Hansen <dave.hansen@...ux.intel.com>,
Mathias Krause <minipli@...glemail.com>,
Vikas Shivappa <vikas.shivappa@...ux.intel.com>, Kyle Huey
<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>, x86@...nel.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC v10 2/6] x86/entry: Add STACKLEAK erasing the kernel
stack at the end of syscalls
On 29.03.2018 21:38, Shivappa Vikas wrote:
> On Wed, 28 Mar 2018, Alexander Popov wrote:
>
>> + const unsigned long check_depth = STACKLEAK_POISON_CHECK_DEPTH /
>> + sizeof(unsigned long);
>> +
>> + /*
>> + * Let's search for the poison value in the stack.
>> + * Start from the lowest_stack and go to the bottom.
>> + */
>> + while (p > boundary && poison <= check_depth) {
>> + if (*(unsigned long *)p == STACKLEAK_POISON)
>> + poison++;
>> + else
>> + poison = 0;
>> +
>> + p -= sizeof(unsigned long);
>> + }
>> +
>> + /*
>> + * One long int at the bottom of the thread stack is reserved and
>> + * should not be poisoned (see CONFIG_SCHED_STACK_END_CHECK).
>> + */
>> + if (p == boundary)
>> + p += sizeof(unsigned long);
>> +
>> + /*
>> + * So let's write the poison value to the kernel stack.
>> + * Start from the address in p and move up till the new boundary.
>> + */
>> + if (on_thread_stack())
>> + boundary = current_stack_pointer;
>> + else
>> + boundary = current_top_of_stack();
>> +
>> + BUG_ON(boundary - p >= THREAD_SIZE);
>> +
>> + while (p < boundary) {
>> + *(unsigned long *)p = STACKLEAK_POISON;
>> + p += sizeof(unsigned long);
>> + }
>
> Sorry catching up late on this.
Hello Vikas,
You are just in time! Thank you for looking at the code.
> can we use a stosq or something here ? wondering
> if that helps get more performance. since you seem to copy the whole stack with
> the poison value. If that was already discussed sorry for the spam :)
Yes, the previous version of the patch series had this function written in
assembly. It used scasq for the poison searching and then stosq for writing:
http://www.openwall.com/lists/kernel-hardening/2018/03/03/9
That amount of assembly was blamed by the maintainers. So I've done my best to
rework it in C bypassing the pitfalls:
http://www.openwall.com/lists/kernel-hardening/2018/03/21/4
In fact, this implementation is not much slower than the assembly one, since we
erase only the used part of the thread stack. This is achieved by the
lowest_stack variable, which is updated during the syscall (please see the next
patch of the series).
Best regards,
Alexander
Powered by blists - more mailing lists
Confused about mailing lists and their use?
Read about mailing lists on Wikipedia
and check out these
guidelines on proper formatting of your messages.
