linux-kernel - Re: [PATCH v38 21/24] x86/vdso: Implement a vDSO for Intel SGX enclave call

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Message-ID: <20200928205636.GB2705@linux.intel.com>
Date:   Mon, 28 Sep 2020 23:56:36 +0300
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     "Yu, Yu-cheng" <yu-cheng.yu@...el.com>
Cc:     Andrew Cooper <andrew.cooper3@...rix.com>, x86@...nel.org,
        linux-sgx@...r.kernel.org, linux-kernel@...r.kernel.org,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Andy Lutomirski <luto@...capital.net>,
        Jethro Beekman <jethro@...tanix.com>,
        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,
        josh@...htriplett.org, 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,
        "H.J. Lu" <hjl.tools@...il.com>
Subject: Re: [PATCH v38 21/24] x86/vdso: Implement a vDSO for Intel SGX
 enclave call

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