linux-kernel - Re: [PATCH v20 00/28] Intel SGX1 support

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Date:   Fri, 10 May 2019 18:04:40 +0000
From:   Jethro Beekman <jethro@...tanix.com>
To:     Dave Hansen <dave.hansen@...el.com>,
        "Xing, Cedric" <cedric.xing@...el.com>,
        Andy Lutomirski <luto@...nel.org>
CC:     Thomas Gleixner <tglx@...utronix.de>,
        "Dr. Greg" <greg@...ellic.com>,
        Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>, X86 ML <x86@...nel.org>,
        "linux-sgx@...r.kernel.org" <linux-sgx@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Christopherson, Sean J" <sean.j.christopherson@...el.com>,
        "nhorman@...hat.com" <nhorman@...hat.com>,
        "npmccallum@...hat.com" <npmccallum@...hat.com>,
        "Ayoun, Serge" <serge.ayoun@...el.com>,
        "Katz-zamir, Shay" <shay.katz-zamir@...el.com>,
        "Huang, Haitao" <haitao.huang@...el.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        "Svahn, Kai" <kai.svahn@...el.com>, Borislav Petkov <bp@...en8.de>,
        Josh Triplett <josh@...htriplett.org>,
        "Huang, Kai" <kai.huang@...el.com>,
        David Rientjes <rientjes@...gle.com>
Subject: Re: [PATCH v20 00/28] Intel SGX1 support

On 2019-05-10 10:54, Dave Hansen wrote:
> On 5/10/19 10:37 AM, Jethro Beekman wrote:
>> It does assume a specific format, namely, that the memory layout
>> (including page types/permissions) of the enclave can be represented in
>> a "flat file" on disk, or at least that the enclave memory contents
>> consist of 4096-byte chunks in that file.
> 
> I _think_ Cedric's point is that, to the kernel,
> /lib/x86_64-linux-gnu/libc.so.6 is a "flat file" because the kernel
> doesn't have any part in parsing the executable format of a shared library.
> 
> I actually don't know how it works, though.  Do we just just trust that
> the userspace parsing of the .so format is correct?  Do we just assume
> that any part of a file passing IMA checks can be PROT_EXEC?
> 

ELF files are explicitly designed such that you can map them (with mmap) 
in 4096-byte chunks. However, sometimes there's overlap and you will 
sometimes see that a particular offset is mapped twice because the first 
half of the page in the file belongs to an RX range and the second half 
to an R-only range. Also, ELF files don't (normally) describe stack, 
heap, etc. which you do need for enclaves.

--
Jethro Beekman | Fortanix


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