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

[Jarkko Sakkinen]

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