linux-kernel - Re: [PATCH v19,RESEND 24/27] x86/vdso: Add __vdso_sgx_enter_enclave() to wrap SGX enclave transitions

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Date:   Wed, 3 Apr 2019 16:03:17 -0700
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     "Xing, Cedric" <cedric.xing@...el.com>,
        Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "x86@...nel.org" <x86@...nel.org>,
        "linux-sgx@...r.kernel.org" <linux-sgx@...r.kernel.org>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "Hansen, Dave" <dave.hansen@...el.com>,
        "nhorman@...hat.com" <nhorman@...hat.com>,
        "npmccallum@...hat.com" <npmccallum@...hat.com>,
        "Ayoun, Serge" <serge.ayoun@...el.com>,
        "Katz-zamir, Shay" <shay.katz-zamir@...el.com>,
        "Huang, Haitao" <haitao.huang@...el.com>,
        "andriy.shevchenko@...ux.intel.com" 
        <andriy.shevchenko@...ux.intel.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "Svahn, Kai" <kai.svahn@...el.com>, "bp@...en8.de" <bp@...en8.de>,
        "josh@...htriplett.org" <josh@...htriplett.org>,
        "Huang, Kai" <kai.huang@...el.com>,
        "rientjes@...gle.com" <rientjes@...gle.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Haitao Huang <haitao.huang@...ux.intel.com>,
        Jethro Beekman <jethro@...tanix.com>,
        "Dr . Greg Wettstein" <greg@...ellic.com>
Subject: Re: [PATCH v19,RESEND 24/27] x86/vdso: Add
 __vdso_sgx_enter_enclave() to wrap SGX enclave transitions

On Thu, Mar 28, 2019 at 12:18:40PM -0700, Andy Lutomirski wrote:
> Finally, why does the vDSO code bother checking whether the leaf is valid?

To sanity check the input to ensure the caller is attempting to enter an
enclave, i.e. the function is named __vdso_sgx_enter_enclave(), not
__vsgx_enclu().  And if the caller does pass the wrong leaf, EINVAL will
be easier to debug than EFAULT, especially on SGX1 hardware where the #GP
could be misconstrued as a loss of EPC.

I'm not dead set on the checks by any means, but it does seem appropriate.
And the cost is all of 3 uops and a few bytes of a code.