Re: [edk2-devel] CPU hotplug using SMM with QEMU+OVMF

[Paolo Bonzini <pbonzini@redhat.com>]

On 17/08/19 02:20, Yao, Jiewen wrote:
> [Jiewen] That is OK. Then we MUST add the third adversary.
> -- Adversary: Simple hardware attacker, who can use device to perform DMA attack in the virtual world.
> NOTE: The DMA attack in the real world is out of scope. That is be handled by IOMMU in the real world, such as VTd. -- Please do clarify if this is TRUE.
> 
> In the real world:
> #1: the SMM MUST be non-DMA capable region.
> #2: the MMIO MUST be non-DMA capable region.
> #3: the stolen memory MIGHT be DMA capable region or non-DMA capable
> region. It depends upon the silicon design.
> #4: the normal OS accessible memory - including ACPI reclaim, ACPI
> NVS, and reserved memory not included by #3 - MUST be DMA capable region.
> As such, IOMMU protection is NOT required for #1 and #2. IOMMU
> protection MIGHT be required for #3 and MUST be required for #4.
> I assume the virtual environment is designed in the same way. Please
> correct me if I am wrong.
> 

Correct.  The 0x30000...0x3ffff area is the only problematic one;
Igor's idea (or a variant, for example optionally remapping
0xa0000..0xaffff SMRAM to 0x30000) is becoming more and more attractive.

Paolo