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Subject: Re: [PATCH v38 21/24] x86/vdso: Implement a vDSO for Intel SGX
 enclave call
To:     Andrew Cooper <andrew.cooper3@citrix.com>,
        Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>,
        x86@kernel.org, linux-sgx@vger.kernel.org
Cc:     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>
References: <20200915112842.897265-1-jarkko.sakkinen@linux.intel.com>
 <20200915112842.897265-22-jarkko.sakkinen@linux.intel.com>
 <721ca14e-21df-3df1-7bef-0b00d0ff90c3@citrix.com>
From:   "Yu, Yu-cheng" <yu-cheng.yu@intel.com>
Message-ID: <c1b0019d-d3cb-cc62-f47f-90c2550c22a4@intel.com>
Date:   Mon, 28 Sep 2020 08:43:16 -0700
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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

> 
> Whichever of these two large series lands first is going to inflict
> fixing this problem on the other.
> 
> As the vdso text is global (to a first approximation), it must not be a
> retpoline if any other process is liable to want to use CET-SS.
> 
> If the retpoline really does need to stay, then the vdso probably needs
> to gain suitable __x86_indirect_thunk_%reg thunks which are patched at
> boot based on the system properties.
> 
> ~Andrew
>