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Comment: Re:uh - by design? (Score 1) 162

by dgatwood (#48670849) Attached to: Thunderbolt Rootkit Vector

All drivers on OS X are already required to tell the operating system ahead of time that a device is about to DMA to memory. That's how that VT-d is able to configure the IOMMU hardware to allow those devices to access RAM without worrying about 64-bit address spaces. So the OS already knows precisely which pages of physical RAM should be accessible by PCIe devices using DMA. If other pages of RAM are accessible, that's a bug.

Similarly, making the Thunderbolt controller's IOMMU mappings be driven by that part of the kernel should not break any drivers at all, by definition, because PCIe devices shouldn't be issuing DMA requests except at driver-preapproved locations. So AFAIK, the only way such a fix could break any device would be if that device was trying to do something really dangerous, like reprogramming one of the PCI bus bridges, or reflashing the computer's EFI firmware....

I mean, I suppose that some drivers might be inadvertently configuring a mapping for a page of memory that also contains executable code or class instances (with function pointers), in which case fully fixing this would also require Apple to modify the IOMemoryDescriptor class to ensure that the DMA-enabled pages are whole pages owned by the descriptor, but that should still be pretty minor, and should result in only a modest amount of wired kernel memory bloat.

In the worst case, such a change might require a CPU-driven copy-on-prepare and/or copy-on-complete to work around drivers that provide their own virtual addresses for a memory descriptor that aren't page-aligned, which would cause a big performance hit for those few drivers, but I'd expect most driver developers to quickly fix those design mistakes to eliminate the performance hit. (And that's assuming this isn't done already—for some reason, I thought those buffers had to be page aligned or you'd get a panic, but I'm not seeing anything about it in the docs, so I might be remembering wrong.)

Comment: Re:I'll play the Grinch (Score 1) 57

by sjames (#48669193) Attached to: The History of the NORAD/Microsoft and Google Santa Trackers

So to translate, "other than a perfectly valid and rational reason that I'd rather not consider, can you tell me a rational and logical reason?"

But as to the question, every culture has a mythos that (hopefully) reminds it's members of their values and provides for a commonality and a sense of belonging. Naturally, children tend to take it all literally. Why spoil their fun Mr. Grinch?

Comment: Re:Violence against police ... (Score 1) 350

by sjames (#48668337) Attached to: Study: Police Body-Cams Reduce Unacceptable Use of Force

Look on the right hand side. There's an awful lot of those 'exceptions'. Way too many. And way too many are later found blameless and put right back out there to do it again.

That needs to stop. It's not all cops, but it's enough of them that it's eroding the public trust. That, in turn will cause more violence against cops as regular citizens begin to fear for their own safety when they encounter police. With all those 'exceptions', is it REALLY unbelievable if a citizen attacks a cop and says he did it because he was in fear of his life? If the cops really want to be safer out there, they need to make certain that the idea of a cop attacking a citizen unprovoked or way out of proportion to provocation is laughable.

Comment: Re:Alternatives (Score 1) 82

by sjames (#48665497) Attached to: Comcast-TWC Merger Review On Hold

On the technical side, they have the ability to control what load a single customer can put on the shared bandwidth. They tell the cable modem and router behind it where the gateway is. They can share the last mile by each provider renting a slice of the (virtual) connection between CO and customer and can recognize their customers by MAC address to give them the correct GW.

The rest is a matter of business. The local government could buy them out. They could be legally split like AT&T. They could simply be informed that they are now in the wholesale last mile bandwidth business if they want to stay in town at all. Note that at that point if they decide they'd rather leave they would end up abandoning the cables amps, etc anyway since it would cost more than it's worth to save it. The town would just need to re-construct the head ends.

FORTRAN rots the brain. -- John McQuillin

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