linux-kernel - Re: [RFC PATCH v1 3/3] selftests/x86: Augment SGX selftest to test new __vdso_sgx_enter

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Message-ID: <20190423014802.GA6749@linux.intel.com>
Date:   Mon, 22 Apr 2019 18:48:02 -0700
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     Cedric Xing <cedric.xing@...el.com>,
        LKML <linux-kernel@...r.kernel.org>, X86 ML <x86@...nel.org>,
        linux-sgx@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Dave <dave.hansen@...el.com>, nhorman@...hat.com,
        npmccallum@...hat.com, Serge <serge.ayoun@...el.com>,
        Shay <shay.katz-zamir@...el.com>,
        Haitao <haitao.huang@...el.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Kai <kai.svahn@...el.com>, Borislav Petkov <bp@...en8.de>,
        Josh Triplett <josh@...htriplett.org>,
        Kai <kai.huang@...el.com>, David Rientjes <rientjes@...gle.com>,
        Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
Subject: Re: [RFC PATCH v1 3/3] selftests/x86: Augment SGX selftest to test
 new __vdso_sgx_enter_enclave() and its callback interface

On Mon, Apr 22, 2019 at 06:29:06PM -0700, Andy Lutomirski wrote:
> On Mon, Apr 22, 2019 at 5:37 PM Cedric Xing <cedric.xing@...el.com> wrote:
> >
> > Given the changes to __vdso_sgx_enter_enclave(), the selftest is augmented to
> > test the newly added callback interface. This addtional test marks the whole
> > enclave range as PROT_READ, and calls mprotect() upon #PFs to add necessary PTE
> > permissions per PFEC (#PF Error Code) until the enclave finishes.
> 
> Nifty.
> 
> What's not tested here is running this code with EFLAGS.TF set and
> making sure that it unwinds correctly.  Also, Jarkko, unless I missed
> something, the vDSO extable code likely has a bug.  If you run the
> instruction right before ENCLU with EFLAGS.TF set, then do_debug()
> will eat the SIGTRAP and skip to the exception handler.  Similarly, if
> you put an instruction breakpoint on ENCLU, it'll get skipped.  Or is
> the code actually correct and am I just remembering wrong?

My money would be on the code being broken as opposed to you remembering
wrong.  I'll take a look at it tomorrow.