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

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Date:   Fri, 19 Apr 2019 21:05:44 +0000
From:   Jethro Beekman <jethro@...tanix.com>
To:     Thomas Gleixner <tglx@...utronix.de>
CC:     Andy Lutomirski <luto@...nel.org>, "Dr. Greg" <greg@...ellic.com>,
        Dave Hansen <dave.hansen@...el.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 2019-04-19 13:46, Jethro Beekman wrote:
> On 2019-04-19 13:39, Thomas Gleixner wrote:
>> On Fri, 19 Apr 2019, Jethro Beekman wrote:
>>
>>> On 2019-04-19 08:27, Andy Lutomirski wrote:
>>>> There are many,
>>>> many Linux systems that enforce a policy that *all* executable text
>>>> needs to come from a verified source.  On these systems, you can't
>>>> mmap some writable memory, write to it, and then change it to
>>>> executable.
>>>
>>> How is this implemented on those systems? AFAIK there's no kernel config
>>> option that changes the semantics of mmap as you describe.
>>
>> That has nothing to do with mmap() semantics. You mmap() writeable memory
>> and then you change the permissions via mprotect(). mprotect() calls into
>> LSM and depending on policy and security model this will reject the
>> request.
>>
>> Andy was pointing out that the SGX ioctl bypasses the LSM mechanics which
>> is obviously a bad thing.
> 
> We could modify the driver such that when you call ioctl EADD, the page
> table permissions need to be the PAGEINFO.SECINFO.FLAGS | PROT_WRITE,
> otherwise you get EPERM or so. After EADD, if you want, you can restrict

Actually, I don't think you even need to include PAGEINFO.SECINFO.FLAGS,
you just need to ensure PROT_WRITE. Regular page table checks take care
of PAGEINFO.SECINFO.FLAGS.

--
Jethro Beekman | Fortanix