linux-kernel - Re: RFC: userspace exception fixups

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Date:   Tue, 06 Nov 2018 09:19:10 -0800
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Andy Lutomirski <luto@...capital.net>
Cc:     Andy Lutomirski <luto@...nel.org>, Jann Horn <jannh@...gle.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Rich Felker <dalias@...c.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Jethro Beekman <jethro@...tanix.com>,
        Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>,
        Florian Weimer <fweimer@...hat.com>,
        Linux API <linux-api@...r.kernel.org>, X86 ML <x86@...nel.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>, nhorman@...hat.com,
        npmccallum@...hat.com, "Ayoun, Serge" <serge.ayoun@...el.com>,
        shay.katz-zamir@...el.com, linux-sgx@...r.kernel.org,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Carlos O'Donell <carlos@...hat.com>,
        adhemerval.zanella@...aro.org
Subject: Re: RFC: userspace exception fixups

On Tue, 2018-11-06 at 08:57 -0800, Andy Lutomirski wrote:
>
> So I guess the non-enclave code basically can’t trust its stack pointer
> because of these shenanigans. And the AEP code has to live with the fact
> that its RSP is basically arbitrary and probably can’t even be unwound
> by a debugger?

The SDK provides a Python GDB plugin to hook into the out-call flow and
do more stack shenanigans.  From what I can tell it's fudging the stack
to make it look like a normal stack frame so the debugger can do it's
thing.

> And the EENTER code has to deal with the fact that its red zone can be
> blatantly violated by the enclave?

That's my understanding of things.  So yeah, if it wasn't obvious before,
the trusted and untrusted parts of the SDK are very tightly coupled.