Subject: Re: [PATCH v2 0/5] Optionally randomize kernel stack offset each syscall

From: Kees Cook <[email-masked]>
Date: Wed, 25 Mar 2020 13:27:02 -0700

On Wed, Mar 25, 2020 at 12:15:12PM +0000, Reshetova, Elena wrote:
> > > Also, are you sure that it isn't possible to make the syscall that
> > > leaked its stack pointer never return to userspace (via ptrace or
> > > SIGSTOP or something like that), and therefore never realign its
> > > stack, while keeping some controlled data present on the syscall's
> > > stack?
> 
> How would you reliably detect that a stack pointer has been leaked
> to userspace while it has been in a syscall? Does not seem to be a trivial
> task to me. 

Well, my expectation is that folks using this defense are also using
panic_on_warn sysctl, etc, so attackers don't get a chance to actually
_use_ register values spilled to dmesg.

-- 
Kees Cook

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