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

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Date:   Mon, 28 Sep 2020 15:18:15 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     "H.J. Lu" <hjl.tools@...il.com>,
        Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
Cc:     Andy Lutomirski <luto@...nel.org>,
        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>,
        Jethro Beekman <jethro@...tanix.com>,
        Cedric Xing <cedric.xing@...el.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        asapek@...gle.com, Borislav Petkov <bp@...en8.de>,
        chenalexchen@...gle.com, Conrad Parker <conradparker@...gle.com>,
        cyhanish@...gle.com, "Huang, Haitao" <haitao.huang@...el.com>,
        Josh Triplett <josh@...htriplett.org>,
        "Huang, Kai" <kai.huang@...el.com>,
        "Svahn, Kai" <kai.svahn@...el.com>, Keith Moyer <kmoy@...gle.com>,
        Christian Ludloff <ludloff@...gle.com>,
        Neil Horman <nhorman@...hat.com>,
        Nathaniel McCallum <npmccallum@...hat.com>,
        Patrick Uiterwijk <puiterwijk@...hat.com>,
        David Rientjes <rientjes@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>, yaozhangx@...gle.com,
        Yu-cheng Yu <yu-cheng.yu@...el.com>
Subject: Re: [PATCH v38 21/24] x86/vdso: Implement a vDSO for Intel SGX
 enclave call

On 9/28/20 3:06 PM, H.J. Lu wrote:
>> I'm open to do either solution. My thinking was to initially do things
>> vsgx.S local (i.e. consider ALTERNATIVE post upstreaming) and use the
>> above solution but I'm also fine doing ALTERNATIVE. Dave kindly briefed
>> on details how that thing works and it should be perfectly usable for
>> our use case.
>>
> Since SHSTK and IBT are enabled per process, not the whole machine,
> are you going to patch vDSO on a per-process basis?

No.

Retpolines mitigate Spectre v2 attacks.  If you're not vulnerable to
Spectre v2, you don't need retpolines.

All processors which support CET *also* have hardware mitigations
against Spectre v2 and don't need retpolines.  Here's all of the
possibilities:

CET=y, BUG_SPECTRE_V2=y: does not exist
CET=n, BUG_SPECTRE_V2=y: vulnerable, use retpoline
CET=y, BUG_SPECTRE_V2=n: no retpoline, not vulnerable
CET=n, BUG_SPECTRE_V2=n: no retpoline, not vulnerable