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

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Date:   Tue, 17 Mar 2020 14:40:34 -0700
From:   "Xing, Cedric" <cedric.xing@...el.com>
To:     Nathaniel McCallum <npmccallum@...hat.com>
Cc:     Sean Christopherson <sean.j.christopherson@...el.com>,
        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>,
        Patrick Uiterwijk <puiterwijk@...hat.com>,
        Andy Lutomirski <luto@...capital.net>,
        Jethro Beekman <jethro@...tanix.com>,
        Connor Kuehl <ckuehl@...hat.com>,
        Harald Hoyer <harald@...hat.com>,
        Lily Sturmann <lsturman@...hat.com>
Subject: Re: [PATCH v28 21/22] x86/vdso: Implement a vDSO for Intel SGX
 enclave call

Hi Nathaniel,

I reread your email today and thought I might have misunderstood your 
email earlier. What changes are you asking for exactly? Is that just 
passing @leaf in %ecx rather than in %eax? If so, I wouldn't have any 
problem. I agree with you that the resulted API would then be callable 
from C, even though it wouldn't be able to return back to C due to 
tampered %rbx. But I think the vDSO API can preserve %rbx too, given it 
is used by both EENTER and EEXIT (so is unavailable for parameter 
passing anyway). Alternatively, the C caller can setjmp() to be 
longjmp()'d back from within the exit handler.

-Cedric