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

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Date:   Tue, 29 Sep 2020 00:36:25 +0300
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     "H.J. Lu" <hjl.tools@...il.com>
Cc:     "Yu, Yu-cheng" <yu-cheng.yu@...el.com>,
        Andrew Cooper <andrew.cooper3@...rix.com>,
        the arch/x86 maintainers <x86@...nel.org>,
        linux-sgx@...r.kernel.org, LKML <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>,
        Andrew Morton <akpm@...ux-foundation.org>,
        andriy.shevchenko@...ux.intel.com, asapek@...gle.com,
        Borislav Petkov <bp@...en8.de>, chenalexchen@...gle.com,
        conradparker@...gle.com, cyhanish@...gle.com,
        Dave Hansen <dave.hansen@...el.com>,
        "Huang, Haitao" <haitao.huang@...el.com>, josh@...htriplett.org,
        kai.huang@...el.com, kai.svahn@...el.com, kmoy@...gle.com,
        Christian Ludloff <ludloff@...gle.com>,
        Andy Lutomirski <luto@...nel.org>, nhorman@...hat.com,
        npmccallum@...hat.com, puiterwijk@...hat.com, rientjes@...gle.com,
        Thomas Gleixner <tglx@...utronix.de>, yaozhangx@...gle.com
Subject: Re: [PATCH v38 21/24] x86/vdso: Implement a vDSO for Intel SGX
 enclave call

On Mon, Sep 28, 2020 at 08:54:01AM -0700, H.J. Lu wrote:
> On Mon, Sep 28, 2020 at 8:43 AM Yu, Yu-cheng <yu-cheng.yu@...el.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.

I have the now full picture of the problem thanks to Andrew's response
[1]. And Dave Hansen just explained me in detail the context and
background with [2]. So I'd guess this will get sorted out soon.

If you don't mind I'll CC you to this commit when I send the next
version?

[1] https://lkml.org/lkml/2020/9/28/1153
[2] https://lkml.org/lkml/2020/9/25/1122

/Jarkko