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Date:   Mon, 28 Sep 2020 23:56:36 +0300
From:   Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
To:     "Yu, Yu-cheng" <yu-cheng.yu@intel.com>
Cc:     Andrew Cooper <andrew.cooper3@citrix.com>, x86@kernel.org,
        linux-sgx@vger.kernel.org, linux-kernel@vger.kernel.org,
        Sean Christopherson <sean.j.christopherson@intel.com>,
        Andy Lutomirski <luto@amacapital.net>,
        Jethro Beekman <jethro@fortanix.com>,
        Cedric Xing <cedric.xing@intel.com>, akpm@linux-foundation.org,
        andriy.shevchenko@linux.intel.com, asapek@google.com, bp@alien8.de,
        chenalexchen@google.com, conradparker@google.com,
        cyhanish@google.com, dave.hansen@intel.com, haitao.huang@intel.com,
        josh@joshtriplett.org, kai.huang@intel.com, kai.svahn@intel.com,
        kmoy@google.com, ludloff@google.com, luto@kernel.org,
        nhorman@redhat.com, npmccallum@redhat.com, puiterwijk@redhat.com,
        rientjes@google.com, tglx@linutronix.de, yaozhangx@google.com,
        "H.J. Lu" <hjl.tools@gmail.com>
Subject: Re: [PATCH v38 21/24] x86/vdso: Implement a vDSO for Intel SGX
 enclave call
Message-ID: <20200928205636.GB2705@linux.intel.com>
References: <20200915112842.897265-1-jarkko.sakkinen@linux.intel.com>
 <20200915112842.897265-22-jarkko.sakkinen@linux.intel.com>
 <721ca14e-21df-3df1-7bef-0b00d0ff90c3@citrix.com>
 <c1b0019d-d3cb-cc62-f47f-90c2550c22a4@intel.com>
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Precedence: bulk

On Mon, Sep 28, 2020 at 08:43:16AM -0700, Yu, Yu-cheng wrote:
> On 9/25/2020 11:23 AM, Andrew Cooper wrote:
> > On 15/09/2020 12:28, Jarkko Sakkinen wrote:
> > > diff --git a/arch/x86/entry/vdso/vsgx_enter_enclave.S b/arch/x86/entry/vdso/vsgx_enter_enclave.S
> > > new file mode 100644
> > > index 000000000000..adbd59d41517
> > > --- /dev/null
> > > +++ b/arch/x86/entry/vdso/vsgx_enter_enclave.S
> > > @@ -0,0 +1,157 @@
> > > +SYM_FUNC_START(__vdso_sgx_enter_enclave)
> > > <snip>
> > > +.Lretpoline:
> > > +	call	2f
> > > +1:	pause
> > > +	lfence
> > > +	jmp	1b
> > > +2:	mov	%rax, (%rsp)
> > > +	ret
> > 
> > I hate to throw further spanners in the work, but this is not compatible
> > with CET, and the user shadow stack work in progress.
> 
> Hi Jarkko,
> 
> These 1: and 2: targets are reached only from these few lines?  If they are
> direct call/jmp targets, I think it is OK in terms of CET.  If they are
> reached from an instruction like "jmp *%rax", then we need to put in an
> "endbr64".
> 
> Yu-cheng

The invocation is over here:

	/* Load the callback pointer to %rax and invoke it via retpoline. */
	mov	SGX_ENCLAVE_RUN_USER_HANDLER(%rax), %rax
	call	.Lretpoline

/Jarkko