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SubjectRe: [PATCH v20 00/28] Intel SGX1 support
On Fri, 19 Apr 2019, 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
> the page table permissions again using mprotect but the page table
> permissions don't really matter for SGX.

And the point of that is? That you still can cirumvent LSM for feeding
executable code into SGX.

No, we are not making special cases and exceptions for SGX.

Thanks,

tglx

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