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Date: Wed, 15 Nov 2017 01:03:58 +0300
From: Alexander Popov <>
To: Andy Lutomirski <>
Cc: Mark Rutland <>,
 "" <>,
 Kees Cook <>, PaX Team <>,
 Brad Spengler <>, Ingo Molnar <>,
 Peter Zijlstra <>, Tycho Andersen <>,
 Laura Abbott <>, Ard Biesheuvel
 <>, Borislav Petkov <>,
 Thomas Gleixner <>, "H . Peter Anvin" <>,
 X86 ML <>
Subject: Re: [PATCH RFC v5 2/5] gcc-plugins: Add STACKLEAK plugin for tracking
 the kernel stack

On 15.11.2017 00:17, Andy Lutomirski wrote:
> On Tue, Nov 14, 2017 at 1:09 PM, Alexander Popov <> wrote:
>> Thanks, Mark!
>> Please see my comments below.
>> On 14.11.2017 19:33, Mark Rutland wrote:
>>> On Tue, Nov 14, 2017 at 08:13:43AM -0800, Andy Lutomirski wrote:
>>>> What does the STEAKLACK plugin actually do?  I haven't followed this enough.
>>> The plugin adds instrumentation to track the maximum stack depth, though only
>>> functions with a sufficiently large stackframe are instrumented.
>> Yes. Functions with a big stack frame call track_stack() to update the
>> lowest_stack value. If CONFIG_VMAP_STACK is disabled, track_stack() is compiled
>> with a check for detecting stack depth overflow. This check is what I'm asking
>> about.
> Then you'll probably have to do something like what I did in the
> VMAP_STACK code.


> That being said, I don't entirely see the point.  If you want a
> hardened kernel, you're going to enable VMAP_STACK.  Are there really
> users of hardened 32-bit kernels?

You know, STACKLEAK already supports x86_32. It's a pity for me to make
STACKLEAK dependent on VMAP_STACK and hence to drop STACKLEAK support for this

I hope there is a way to add a good-looking check to track_stack() and have at
least some profit (although it will not catch all overflow cases).

Best regards,

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