linux-kernel - Re: [PATCH v28 21/22] x86/vdso: Implement a vDSO for Intel SGX enclave call

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Date:   Fri, 13 Mar 2020 09:33:26 -0700
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Nathaniel McCallum <npmccallum@...hat.com>
Cc:     Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>,
        linux-kernel@...r.kernel.org, x86@...nel.org,
        linux-sgx@...r.kernel.org, akpm@...ux-foundation.org,
        dave.hansen@...el.com, Neil Horman <nhorman@...hat.com>,
        "Huang, Haitao" <haitao.huang@...el.com>,
        andriy.shevchenko@...ux.intel.com, tglx@...utronix.de,
        "Svahn, Kai" <kai.svahn@...el.com>, bp@...en8.de,
        Josh Triplett <josh@...htriplett.org>, luto@...nel.org,
        kai.huang@...el.com, David Rientjes <rientjes@...gle.com>,
        cedric.xing@...el.com, Patrick Uiterwijk <puiterwijk@...hat.com>,
        Andy Lutomirski <luto@...capital.net>,
        Jethro Beekman <jethro@...tanix.com>
Subject: Re: [PATCH v28 21/22] x86/vdso: Implement a vDSO for Intel SGX
 enclave call

On Fri, Mar 13, 2020 at 12:07:55PM -0400, Nathaniel McCallum wrote:
> On Thu, Mar 12, 2020 at 8:52 PM Sean Christopherson
> <sean.j.christopherson@...el.com> wrote:
> > FWIW, if the handler reaaaly wanted to pop off the stack, it could do so,
> > fixup the stack, and then re-call __vdso_sgx_enter_enclave() instead of
> > returning (to the original __vdso_sgx_enter_enclave()).
> 
> My understanding from the documentation issue above was that *if* you
> wanted to push parameters back on the stack during enclave exit, you
> would *have* to supply a handler so it could pop the parameters and
> reset the stack. Which is why restoring %rsp from %rbx didn't make
> sense to me.

Yep.