Commit 49e9c99f authored Jun 29, 2016 by Ian Munsie Committed by Michael Ellerman Jul 08, 2016

cxl: Fix allowing bogus AFU descriptors with 0 maximum processes



If the AFU descriptor of an AFU directed AFU indicates that it supports
0 maximum processes, we will accept that value and attempt to use it.
The SPA will still be allocated (with 2 pages due to another minor bug
and room for 958 processes), and when a context is allocated we will
pass the value of 0 to idr_alloc as the maximum. However, idr_alloc will
treat that as meaning no maximum and will allocate a context number and
we return a valid context.

Conceivably, this could lead to a buffer overflow of the SPA if more
than 958 contexts were allocated, however this is mitigated by the fact
that there are no known AFUs in the wild with a bogus AFU descriptor
like this, and that only the root user is allowed to flash an AFU image
to a card.

Add a check when validating the AFU descriptor to reject any with 0
maximum processes.

We do still allow a dedicated process only AFU to indicate that it
supports 0 contexts even though that is forbidden in the architecture,
as in that case we ignore the value and use 1 instead. This is just on
the off-chance that such a dedicated process AFU may exist (not that I
am aware of any), since their developers are less likely to have cared
about this value at all.

Signed-off-by: Ian Munsie <imunsie@au1.ibm.com>
Reviewed-by: Frederic Barrat <fbarrat@linux.vnet.ibm.com>
Reviewed-by: Andrew Donnellan <andrew.donnellan@au1.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

parent bdd91001

drivers/misc/cxl/pci.c

+15 −0

Original line number	Diff line number	Diff line
		@@ -775,6 +775,21 @@ static int cxl_afu_descriptor_looks_ok(struct cxl_afu *afu)
		}
		}

		if ((afu->modes_supported & ~CXL_MODE_DEDICATED) && afu->max_procs_virtualised == 0) {
		/*
		* We could also check this for the dedicated process model
		* since the architecture indicates it should be set to 1, but
		* in that case we ignore the value and I'd rather not risk
		* breaking any existing dedicated process AFUs that left it as
		* 0 (not that I'm aware of any). It is clearly an error for an
		* AFU directed AFU to set this to 0, and would have previously
		* triggered a bug resulting in the maximum not being enforced
		* at all since idr_alloc treats 0 as no maximum.
		*/
		dev_err(&afu->dev, "AFU does not support any processes\n");
		return -EINVAL;
		}

		return 0;
		}