Messages in this thread | | | Date | Mon, 21 Aug 2017 19:24:25 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH 3/3] x86/efi: Use efi_switch_mm() rather than manually twiddling with cr3 |
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On Mon, Aug 21, 2017 at 06:56:01AM -0700, Andy Lutomirski wrote: > There are two ways this could be a problem. One is that u privileged > user apps shouldn't be able to read from EFI memory. The other is > that, if EFI were to have IO memory mapped at a "user" address, perf > could end up reading it.
So assuming the efi_switch_mm() case from the calling thread context, I don't see how we can avoid it at all.
Suppose we have a free running PEBS counter (PEBS puts samples in DS buffer and only raises PMI when 'full'). This can easily cover the entire efi_switch_mm() and back swizzle, and then we have 'userspace' samples that don't correspond to actual userspace.
EFI (pretending to be userspace) is a giant trainwreck.
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