linux-kernel - Re: [PATCH v39 21/24] x86/vdso: Implement a vDSO for Intel SGX enclave call

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Message-ID: <20201006151532.GA17610@linux.intel.com>
Date:   Tue, 6 Oct 2020 08:15:32 -0700
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Jethro Beekman <jethro@...tanix.com>
Cc:     Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>, x86@...nel.org,
        linux-sgx@...r.kernel.org, linux-kernel@...r.kernel.org,
        Andy Lutomirski <luto@...capital.net>,
        Cedric Xing <cedric.xing@...el.com>, akpm@...ux-foundation.org,
        andriy.shevchenko@...ux.intel.com, asapek@...gle.com, bp@...en8.de,
        chenalexchen@...gle.com, conradparker@...gle.com,
        cyhanish@...gle.com, dave.hansen@...el.com, haitao.huang@...el.com,
        kai.huang@...el.com, kai.svahn@...el.com, kmoy@...gle.com,
        ludloff@...gle.com, luto@...nel.org, nhorman@...hat.com,
        npmccallum@...hat.com, puiterwijk@...hat.com, rientjes@...gle.com,
        tglx@...utronix.de, yaozhangx@...gle.com, mikko.ylinen@...el.com
Subject: Re: [PATCH v39 21/24] x86/vdso: Implement a vDSO for Intel SGX
 enclave call

On Tue, Oct 06, 2020 at 10:30:16AM +0200, Jethro Beekman wrote:
> On 2020-10-06 04:57, Sean Christopherson wrote:
> > On Sat, Oct 03, 2020 at 07:50:56AM +0300, Jarkko Sakkinen wrote:
> >> +struct sgx_enclave_run {
> >> +  __u64 tcs;
> >> +  __u64 user_handler;
> >> +  __u64 user_data;
> >> +  __u32 leaf;
> >
> > I am still very strongly opposed to omitting exit_reason.  It is not at all
> > difficult to imagine scenarios where 'leaf' alone is insufficient for the
> > caller or its handler to deduce why the CPU exited the enclave.  E.g. see
> > Jethro's request for intercepting interrupts.
>
> Not entirely sure what this has to do with my request, I just expect to see
> leaf=ERESUME in this case, I think? E.g. as you would see in EAX when calling
> ENCLU.

But how would you differentiate from the case that an exception occured in
the enclave?  That will also transfer control with leaf=ERESUME.  If there
was a prior exception and userspace didn't zero out the struct, there would
be "valid" data in the exception fields.

An exit_reason also would allow retrofitting the exception fields into a
union, i.e. the fields are valid if and only if exit_reason is exception.