Messages in this thread |  | | From | Michael Ellerman <> | Subject | Re: [PATCH v6 01/17] powerpc/vas: Define macros, register fields and structures | Date | Wed, 16 Aug 2017 22:07:38 +1000 |
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Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com> writes:
> Nicholas Piggin [npiggin@gmail.com] wrote: >> On Mon, 14 Aug 2017 15:21:48 +1000 >> Michael Ellerman <mpe@ellerman.id.au> wrote: >> >> > Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com> writes: >> >> > > arch/powerpc/include/asm/vas.h | 35 ++++ >> > > arch/powerpc/include/uapi/asm/vas.h | 25 +++ >> > >> > I thought we weren't exposing VAS to userspace yet? >> > >> > If we are then we need to get things straight WRT copy/paste abort. ... > > In the FTW case, there is no data transfer from user space to the hardware. > i.e the copy/paste submit a NULL CRB and hardware will be configured (see > ->fifo_disable setting in winctx) to ignore any data they specify in the CRB.
I thought the copy did copy a cacheline, but then the paste to the VAS window just ignores the contents, and doesn't allow userspace to get the content in any way?
Which means we have two thirds of a covert channel, ie. something can be copied into the copy buffer by one process, and then a second process can paste it, but because it can only paste to foreign memory, and the only foreign memory it can get is a VAS FTW window, it can't actually see the content of the copy buffer.
> Would we be able to allow copy/paste from user space in that case?
Yeah I think so, but it is all a bit fragile.
cheers
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