[Gllug] Anyone having broadband (probably PlusNet) problems today?

[Christian Smith]

On Wed, 30 Mar 2005, Nix wrote:

>On Tue, 29 Mar 2005, Russell Howe whispered secretively:
>> On Tue, Mar 29, 2005 at 10:35:13AM +0100, Nix wrote:
>>> Actaully, in general, if the hardware is DMA-capable, the firmware could
>>> do anything in RAM it liked, including (if the firmware were malicious
>>> or buggy) introducing security holes.
>>>
>>> Disk controllers tend to be DMA-capable. :)
>>
>> True, and I suppose this would bypass the memory protections afforded by
>> the CPU and/or MMU as I guess the DMA transfer would bypass this?
>
>Yeah, DMA is direct-to-physical-memory: you lose.
>
>(This is why scatter-gather support is so important: contiguous virtual
>memory blocks tend to be discontiguous in physical memory...)


It's also why machines such as SUNs have a IOMMU, which provides
protection and linear access to sparse physical memory addresses from IO
cards. The kernel can then only allow IO cards to access the proper memory
required for operation.

Christian

-- 
    /"\
    \ /    ASCII RIBBON CAMPAIGN - AGAINST HTML MAIL
     X                           - AGAINST MS ATTACHMENTS
    / \
-- 
Gllug mailing list  -  Gllug at gllug.org.uk
http://lists.gllug.org.uk/mailman/listinfo/gllug