linux-kernel - Re: [PATCH v33 15/21] x86/vdso: Add support for exception fixup in vDSO functions

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Message-ID: <87mu4i9j06.fsf@nanos.tec.linutronix.de>
Date:   Thu, 02 Jul 2020 14:52:25 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Andy Lutomirski <luto@...capital.net>,
        Borislav Petkov <bp@...en8.de>
Cc:     Sean Christopherson <sean.j.christopherson@...el.com>,
        Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>,
        X86 ML <x86@...nel.org>, linux-sgx@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>,
        Jethro Beekman <jethro@...tanix.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        asapek@...gle.com, "Xing\, Cedric" <cedric.xing@...el.com>,
        chenalexchen@...gle.com, conradparker@...gle.com,
        cyhanish@...gle.com, Dave Hansen <dave.hansen@...el.com>,
        "Huang\, Haitao" <haitao.huang@...el.com>,
        Josh Triplett <josh@...htriplett.org>,
        "Huang\, Kai" <kai.huang@...el.com>,
        "Svahn\, Kai" <kai.svahn@...el.com>, kmoy@...gle.com,
        Christian Ludloff <ludloff@...gle.com>,
        Andrew Lutomirski <luto@...nel.org>,
        Neil Horman <nhorman@...hat.com>, npmccallum@...hat.com,
        puiterwijk@...hat.com, David Rientjes <rientjes@...gle.com>,
        yaozhangx@...gle.com
Subject: Re: [PATCH v33 15/21] x86/vdso: Add support for exception fixup in vDSO functions

Andy Lutomirski <luto@...capital.net> writes:
> On Tue, Jun 30, 2020 at 1:41 AM Borislav Petkov <bp@...en8.de> wrote:
>>
>> On Mon, Jun 29, 2020 at 11:00:55PM -0700, Sean Christopherson wrote:
>> > E.g. the vDSO function should get the fixup even if userspace screws
>> > up mmap() and invokes __vdso_sgx_enter_enclave() without being tagged
>> > an SGX task.
>>
>> I sincerely hope you don't mean this seriously.
>>
>> Please add a member to task_struct which denotes that a task is an
>> sgx task, test that member where needed and forget real quickly about
>> running *any* *fixup* for unrelated tasks.
>
> I don't see the problem.  If you call this magic vDSO function and get
> a fault, it gets handled.  What's the failure mode?

Handled by some definition of handled. If a random user space tasks ends
up in that function then it will not die as it would otherwise, but I
don't see a real issue with that either.

Thanks,

        tglx