[Xen-devel] [PATCH] xen/pciback: Fix conf_space read/write overlap check.

[Andrey Grodzovsky <andrey2805@xxxxxxxxx>]

Current overlap check is evaluating to false a case where a filter field
is fully contained (proper subset) of a r/w request.
This change applies classical overlap check instead to include
all the scenarios.

More specifically, for (Hilscher GmbH CIFX 50E-DP(M/S)) device
driver the logic is such that the entire confspace  is read and
written in 4 byte chunks.In this case as an example, CACHE_LINE_SIZE,
LATENCY_TIMER and PCI_BIST are arriving together in one call to
xen_pcibk_config_write with offset == 0xc and size == 4.
With the exsisting overlap check LATENCY_TIMER field
(offset == 0xd, length == 1) is fully contained in the write request
and hence is excluded from write, which is incorrect.

Related to https://www.mail-archive.com/xen-devel@xxxxxxxxxxxxx/msg72174.html

Reviewed-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
Reviewed-by: David Vrabel <david.vrabel@xxxxxxxxxx>
Cc: Jan Beulich <JBeulich@xxxxxxxx>
Cc: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Andrey Grodzovsky <andrey2805@xxxxxxxxx>
---
 drivers/xen/xen-pciback/conf_space.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/drivers/xen/xen-pciback/conf_space.c 
b/drivers/xen/xen-pciback/conf_space.c
index 8e67336..6a25533 100644
--- a/drivers/xen/xen-pciback/conf_space.c
+++ b/drivers/xen/xen-pciback/conf_space.c
@@ -183,8 +183,7 @@ int xen_pcibk_config_read(struct pci_dev *dev, int offset, 
int size,
                field_start = OFFSET(cfg_entry);
                field_end = OFFSET(cfg_entry) + field->size;
 
-               if ((req_start >= field_start && req_start < field_end)
-                   || (req_end > field_start && req_end <= field_end)) {
+                if (req_end > field_start && field_end > req_start) {
                        err = conf_space_read(dev, cfg_entry, field_start,
                                              &tmp_val);
                        if (err)
@@ -230,8 +229,7 @@ int xen_pcibk_config_write(struct pci_dev *dev, int offset, 
int size, u32 value)
                field_start = OFFSET(cfg_entry);
                field_end = OFFSET(cfg_entry) + field->size;
 
-               if ((req_start >= field_start && req_start < field_end)
-                   || (req_end > field_start && req_end <= field_end)) {
+                if (req_end > field_start && field_end > req_start) {
                        tmp_val = 0;
 
                        err = xen_pcibk_config_read(dev, field_start,
-- 
2.1.4


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