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Re: [Xen-devel] [PATCH 4/4] x86/vLAPIC: avoid speculative out of bounds accesses


  • To: Jan Beulich <JBeulich@xxxxxxxx>, xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
  • From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
  • Date: Thu, 4 Jul 2019 14:44:36 +0100
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  • Cc: Juergen Gross <jgross@xxxxxxxx>, Wei Liu <wei.liu2@xxxxxxxxxx>, nmanthey@xxxxxxxxx, Roger Pau Monne <roger.pau@xxxxxxxxxx>
  • Delivery-date: Thu, 04 Jul 2019 13:44:47 +0000
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On 31/01/2019 14:27, Jan Beulich wrote:
> Array indexes used in the MMIO and MSR read/write emulation functions
> are derived from guest controlled values. Restrict their ranges to limit
> the side effects of speculative execution.
>
> Remove the unused vlapic_lvt_{vector,dm}() instead of adjusting them.
>
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

While they are all guest controlled, the MMIO side of things is on the
end of a function pointer call, which has already determined that the
access is within 4k.  I don't think there any safety concerns here.

guest_rdmsr_x2apic() does get values in the range 0x800...0xbff, so I
think this is the only case which needs protecting.

~Andrew

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