Re: [PATCH 3/7] x86/enter: Use IBRS on syscall and interrupts

Dr. David Alan Gilbert
2018-01-05T12:27:34Z

> Dave Hansen <dave.hansen@intel.com> wrote:
>> On 01/04/2018 08:51 PM, Andy Lutomirski wrote:
>> > Do we need an arch_prctl() to enable IBRS for user mode?
>>
>> Eventually, once the dust settles. I think there's a spectrum of
>> paranoia here, that is roughly (with increasing paranoia):
>>
>> 1. do nothing
>> 2. do retpoline
>> 3. do IBRS in kernel
>> 4. do IBRS always
>>
>> I think you're asking for ~3.5.
>>
>> Patches for 1-3 are out there and 4 is pretty straightforward. Doing a
>> arch_prctl() is still straightforward, but will be a much more niche
>> thing than any of the other choices. Plus, with a user interface, we
>> have to argue over the ABI for at least a month or two. ;)

I was chatting to Andrea about this, and we came to the conclusion one
use might be for qemu; I was worried about (theoretically) whether
userspace in a guest could read privileged data from the guest kernel by
attacking the qemu process rather than by attacking the kernels.

Dave

--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK