Messages in this thread | | | Subject | Re: [PATCH v5 14/28] x86/fpu/xstate: Prevent unauthorised use of dynamic user state | From | Dave Hansen <> | Date | Tue, 29 Jun 2021 12:26:57 -0700 |
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On 6/29/21 12:13 PM, Bae, Chang Seok wrote: >> >> Is it actually important to make sure that they are dynamic features? >> Is there *any* case where a feature (dynamic or not) can have XFD armed >> and be out of its init state? > In this AMX series, XFD is only used for the xstate buffer management. The > code is made in a such way that XFD and dynamic states are a bit coupled. > > But I think XFD can be extended for other usages in the future. Then, yes. > (This warning is also for future code changes.) > > So, reading the MSR is just simple and clean here, but it consumes cycles. Or, > a task may have a field for XFD value per se unless this conversion is > acceptable.
I'm not following.
All that I see here is that you made what could be a very generic check:
Thou shalt never XSAVE a xfeature which is XFD-armed
and made it more specific:
Thou shalt never XSAVE a *dynamic* xfeature which is XFD-armed
I'm just saying that I don't see the value in a less-broad check. Let's make the sanity check as broad as possible. That actually makes the code simpler.
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