Message 2 of 3
27 Dec 17 13:18
Join Date: 28 Jan 2005
Posts To This List: 11891
Initiate DMA without scatter gather list
> In my device driver, upon IOCTL request I have to start DMA from hardware into
> The RAM address passed in the request is a physical address of a continuous
buffer allocated by another device driver.
There is NO WAY you should allow this information to be passed in from
user-mode.Â There's nothing wrong with using a common buffer allocated
by another driver (with appropriate synchronization), but you need to
get the address from the driver directly.Â User-mode code is untrusted
code.Â It is an enormous security hole to accept and use a physical
address from user mode.
> This is a customer requirement. I'm aware it's not by the book.
The concept of using a physical address from another driver is fine.Â
The concept of passing that information through user-mode is absolutely
no go, and as a professional driver writer, you have a responsibility to
tell your client that it is not acceptable.Â There are other ways to
accomplish this, securely and reliably.
> The "EvtProgramReadDma" routine passed to
WdfDmaTransactionInitializeusingRequest get the paramater:
> PSCATTER_GATHER_LIST SgList
> But in my case, there is no SG list created by the framework.
> Should I use any WdfDma calls at all ?
Not in this case, no.Â I don't think it gains you anything.Â I have one
driver that has both common buffer DMA for a circular buffer, and
one-shot DMA for user requests.Â The one-shot stuff goes through the
WdfDma abstraction, but the common buffer transactions are handled directly.
Tim Roberts, firstname.lastname@example.org
Providenza & Boekelheide, Inc.