| Date | Tue, 22 Apr 2014 15:55:11 -0400 | Subject | Re: [PATCH] x86-64: espfix for 64-bit mode *PROTOTYPE* | From | Brian Gerst <> |
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On Tue, Apr 22, 2014 at 2:51 PM, H. Peter Anvin <hpa@zytor.com> wrote: > On 04/22/2014 11:17 AM, Brian Gerst wrote: >>> >>> That is the entry condition that we have to deal with. The fact that >>> the switch to the IST is unconditional is what makes ISTs hard to deal with. >> >> Right, that is why you switch away from the IST as soon as possible, >> copying the data that is already pushed there to another stack so it >> won't be overwritten by a recursive fault. >> > > That simply will not work if you can take a #GP due to the "safe" MSR > functions from NMI and #MC context, which would be my main concern.
In that case (#2 above), you would switch to the previous %rsp (in the NMI/MC stack), copy the exception frame from the IST, and continue with the #GP handler. That effectively is the same as it is today, where no stack switch occurs on the #GP fault.
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