Messages in this thread | | | Date | Mon, 15 Jan 2018 11:03:08 +0100 (CET) | From | Thomas Gleixner <> | Subject | Re: Improve retpoline for Skylake |
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On Mon, 15 Jan 2018, Jon Masters wrote: > On 01/12/2018 05:03 PM, Henrique de Moraes Holschuh wrote: > > On Fri, 12 Jan 2018, Andi Kleen wrote: > >>> Skylake still loses if it takes an SMI, right? > >> > >> SMMs are usually rare, especially on servers, and are usually > >> not very predictible, and even if you have > > > > FWIW, a data point: SMIs can be generated on demand by userspace on > > thinkpad laptops, but they will be triggered from within a kernel > > context. I very much doubt this is a rare pattern... > > Sure. Just touch some "legacy" hardware that the vendor emulates in a > nasty SMI handler. It's definitely not acceptable to assume that SMIs > can't be generated under the control of some malicious user code.
We all know that there are holes, but can we finally sit down and do a proper analysis whether they are practically exploitable or not.
A laptop is single user, i.e. the most likely attack vector is java script. So please elaborate how you abuse that from JS.
If the laptop is compromised in a way that malicious code is executed on it outside JS, then the SMI hole is the least of your worries, really.
> Our numbers on Skylake weren't bad, and there seem to be all kinds of > corner cases, so again, it seems as if IBRS is the safest choice.
Talk is cheap. Show numbers comparing the full retpoline/RBS mitigation compared to IBRS.
Thanks,
tglx
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