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From:   "H.J. Lu" <hjl.tools@gmail.com>
Date:   Mon, 28 Sep 2020 08:54:01 -0700
Message-ID: <CAMe9rOrVhQr9ad_4en2D5GTTqDsJGXqszBmscgenn_87mDxvUA@mail.gmail.com>
Subject: Re: [PATCH v38 21/24] x86/vdso: Implement a vDSO for Intel SGX
 enclave call
To:     "Yu, Yu-cheng" <yu-cheng.yu@intel.com>
Cc:     Andrew Cooper <andrew.cooper3@citrix.com>,
        Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>,
        "the arch/x86 maintainers" <x86@kernel.org>,
        linux-sgx@vger.kernel.org, LKML <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>,
        Andrew Morton <akpm@linux-foundation.org>,
        andriy.shevchenko@linux.intel.com, asapek@google.com,
        Borislav Petkov <bp@alien8.de>, chenalexchen@google.com,
        conradparker@google.com, cyhanish@google.com,
        Dave Hansen <dave.hansen@intel.com>,
        "Huang, Haitao" <haitao.huang@intel.com>, josh@joshtriplett.org,
        kai.huang@intel.com, kai.svahn@intel.com, kmoy@google.com,
        Christian Ludloff <ludloff@google.com>,
        Andy Lutomirski <luto@kernel.org>, nhorman@redhat.com,
        npmccallum@redhat.com, puiterwijk@redhat.com, rientjes@google.com,
        Thomas Gleixner <tglx@linutronix.de>, yaozhangx@google.com
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On Mon, Sep 28, 2020 at 8:43 AM Yu, Yu-cheng <yu-cheng.yu@intel.com> 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.