linux-kernel - Re: [PATCH 00/35] Shadow stacks for userspace

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Message-ID: <Yf/K0NCTbjWfO5K6@hirez.programming.kicks-ass.net>
Date:   Sun, 6 Feb 2022 14:19:12 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     "H.J. Lu" <hjl.tools@...il.com>
Cc:     "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>,
        "David.Laight@...lab.com" <David.Laight@...lab.com>,
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Subject: Re: [PATCH 00/35] Shadow stacks for userspace

On Sat, Feb 05, 2022 at 12:21:12PM -0800, H.J. Lu wrote:

> setjmp/longjmp work on the same sigjmp_buf.  Shadow stack pointer
> is saved and restored, just like any other callee-saved registers.

How is having that shadow stack pointer in user-writable memory not a
problem? That seems like a prime target to subvert the whole shadow
stack machinery.