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Date: Mon, 11 Dec 2017 10:26:45 +0100
From: Peter Zijlstra <>
To: Alexander Popov <>
Cc:, Kees Cook <>,
	PaX Team <>,
	Brad Spengler <>,
	Ingo Molnar <>, Andy Lutomirski <>,
	Tycho Andersen <>, Laura Abbott <>,
	Mark Rutland <>,
	Ard Biesheuvel <>,
	Borislav Petkov <>,
	Thomas Gleixner <>,
	"H . Peter Anvin" <>,
Subject: Re: [PATCH RFC v6 1/6] x86/entry: Add STACKLEAK erasing the kernel
 stack at the end of syscalls

On Sat, Dec 09, 2017 at 12:54:21AM +0300, Alexander Popov wrote:
> Hello Peter,
> On 08.12.2017 14:44, Peter Zijlstra wrote:
> > On Wed, Dec 06, 2017 at 02:33:42AM +0300, Alexander Popov wrote:
> >> The STACKLEAK feature erases the kernel stack before returning from
> >> syscalls. That reduces the information which kernel stack leak bugs can
> >> reveal and blocks some uninitialized stack variable attacks. Moreover,
> >> STACKLEAK provides runtime checks for kernel stack overflow detection.
> >>
> >> This commit introduces the architecture-specific code filling the used
> >> part of the kernel stack with a poison value before returning to the
> >> userspace. Full STACKLEAK feature also contains the gcc plugin which
> >> comes in a separate commit.
> > 
> > Have you looked at the entry rework in this series:
> > 
> >
> Thanks for the link. I briefly looked through WIP.x86/pti branch. Should I
> rebase STACKLEAK patch series onto it?

Probably a good idea; the tail end of that series is still somewhat in
flux but the entry rework is fairly stable at this point.

> Although I don't fully understand some of the commits, I can suppose that
> STACKLEAK stack erasing must be modified because of this trampoline stack
> introduction:
> Am I right? Are there other changes which I should consider?

You're right; the trampoline stack is what I was thinking of. You can
run the erase thing when we're on the trampoline back out.

> May I also ask for your feedback on this version of the STACKLEAK patch series?

I meant to have a look, but have not yet found the time for it, its on
the todo list.


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