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

[H.J. Lu]

On Mon, Sep 28, 2020 at 8:43 AM Yu, Yu-cheng <yu-cheng.yu@xxxxxxxxx> 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".
>

This also isn't compatible with shadow stack.

-- 
H.J.