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Re: [Xen-devel] Bisected Xen-unstable: "Segment register inaccessible for d1v0" when starting HVM guest on intel
>>> On 02.07.14 at 12:02, <andrew.cooper3@xxxxxxxxxx> wrote:
>> Just like copy_to_user() would produce -EFAULT for a hypercall
>> when used on a non-present page or a non-canonical address, it
>> should (and afaict will with how things are right now) similarly
>> produce -EFAULT for an attempted access to a guest-accessible
>> page when the current mode of the guest is supervisor.
>>
>> To me it is a logical extension to also fail accesses outside of
>> hypercalls or emulation.
>
> Consider an HVM guest with SMAP in effect, making a hypercall. If a
> guest handle points to guest userspace, Xen would be unable to ever
> complete the hypercall without an -EFAULT.
>
> I don't think this is reasonable to fail.
This is very reasonable to fail: Such an operation violates the SMAP
guarantees. If the kernel wants to permit this, it needs to CLAC/STAC
around the hypercall in its privcmd (or alike) driver.
Jan
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