[PATCH v13 14/14] arm/vpci: honor access size when returning an error

[Stewart Hildebrand <stewart.hildebrand@xxxxxxx>]

From: Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>

Guest can try to read config space using different access sizes: 8,
16, 32, 64 bits. We need to take this into account when we are
returning an error back to MMIO handler, otherwise it is possible to
provide more data than requested: i.e. guest issues LDRB instruction
to read one byte, but we are writing 0xFFFFFFFFFFFFFFFF in the target
register.

Signed-off-by: Volodymyr Babchuk <volodymyr_babchuk@xxxxxxxx>
Signed-off-by: Stewart Hildebrand <stewart.hildebrand@xxxxxxx>
---
v9->10:
* New patch in v10.
---
 xen/arch/arm/vpci.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/xen/arch/arm/vpci.c b/xen/arch/arm/vpci.c
index 348ba0fbc860..aaf9d9120c3d 100644
--- a/xen/arch/arm/vpci.c
+++ b/xen/arch/arm/vpci.c
@@ -41,6 +41,8 @@ static int vpci_mmio_read(struct vcpu *v, mmio_info_t *info,
 {
     struct pci_host_bridge *bridge = p;
     pci_sbdf_t sbdf;
+    const uint8_t access_size = (1 << info->dabt.size) * 8;
+    const uint64_t access_mask = GENMASK_ULL(access_size - 1, 0);
     /* data is needed to prevent a pointer cast on 32bit */
     unsigned long data;
 
@@ -48,7 +50,7 @@ static int vpci_mmio_read(struct vcpu *v, mmio_info_t *info,
 
     if ( !vpci_sbdf_from_gpa(v->domain, bridge, info->gpa, &sbdf) )
     {
-        *r = ~0UL;
+        *r = access_mask;
         return 1;
     }
 
@@ -59,7 +61,7 @@ static int vpci_mmio_read(struct vcpu *v, mmio_info_t *info,
         return 1;
     }
 
-    *r = ~0UL;
+    *r = access_mask;
 
     return 0;
 }
-- 
2.43.0