[xen staging] vpci: restrict unhandled read/write operations for guests

[patchbot@xxxxxxx]

commit 80b0eb095aae5aef62cb529e93cba93f687b0b75
Author:     Oleksandr Andrushchenko <oleksandr_andrushchenko@xxxxxxxx>
AuthorDate: Tue Feb 27 14:53:50 2024 +0100
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Tue Feb 27 14:53:50 2024 +0100

    vpci: restrict unhandled read/write operations for guests
    
    A guest would be able to read and write those registers which are not
    emulated and have no respective vPCI handlers, so it will be possible
    for it to access the hardware directly.
    In order to prevent a guest from reads and writes from/to the unhandled
    registers make sure only hardware domain can access the hardware directly
    and restrict guests from doing so.
    
    Suggested-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
    Signed-off-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@xxxxxxxx>
    Signed-off-by: Volodymyr Babchuk <volodymyr_babchuk@xxxxxxxx>
    Reviewed-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
    Signed-off-by: Stewart Hildebrand <stewart.hildebrand@xxxxxxx>
---
 xen/drivers/vpci/vpci.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/xen/drivers/vpci/vpci.c b/xen/drivers/vpci/vpci.c
index 475272b173..d545dc633c 100644
--- a/xen/drivers/vpci/vpci.c
+++ b/xen/drivers/vpci/vpci.c
@@ -268,6 +268,10 @@ static uint32_t vpci_read_hw(pci_sbdf_t sbdf, unsigned int 
reg,
 {
     uint32_t data;
 
+    /* Guest domains are not allowed to read real hardware. */
+    if ( !is_hardware_domain(current->domain) )
+        return ~(uint32_t)0;
+
     switch ( size )
     {
     case 4:
@@ -311,6 +315,10 @@ static uint32_t vpci_read_hw(pci_sbdf_t sbdf, unsigned int 
reg,
 static void vpci_write_hw(pci_sbdf_t sbdf, unsigned int reg, unsigned int size,
                           uint32_t data)
 {
+    /* Guest domains are not allowed to write real hardware. */
+    if ( !is_hardware_domain(current->domain) )
+        return;
+
     switch ( size )
     {
     case 4:
--
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