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

[Jethro Beekman]

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