[PATCH] vfio/pci: Use defined memcpy() behavior

[Alex Williamson]

vfio_rom_read() relies on memcpy() doing the logically correct thing,
ie. safely copying zero bytes from a NULL pointer when rom_size is
zero, rather than the spec definition, which is undefined when the
source or target pointers are NULL.  Resolve this by wrapping the
call in the condition expressed previously by the ternary.

Additionally, we still use @val to fill data based on the provided
@size regardless of mempcy(), so we should initialize @val rather
than @data.

Reported-by: Longpeng <address@hidden>
Reported-by: Laszlo Ersek <address@hidden>
Signed-off-by: Alex Williamson <address@hidden>
---
 hw/vfio/pci.c |    9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/hw/vfio/pci.c b/hw/vfio/pci.c
index 5e75a95129ac..b0799cdc28ad 100644
--- a/hw/vfio/pci.c
+++ b/hw/vfio/pci.c
@@ -859,16 +859,17 @@ static uint64_t vfio_rom_read(void *opaque, hwaddr addr, 
unsigned size)
         uint16_t word;
         uint32_t dword;
         uint64_t qword;
-    } val;
-    uint64_t data = 0;
+    } val = { 0 };
+    uint64_t data;
 
     /* Load the ROM lazily when the guest tries to read it */
     if (unlikely(!vdev->rom && !vdev->rom_read_failed)) {
         vfio_pci_load_rom(vdev);
     }
 
-    memcpy(&val, vdev->rom + addr,
-           (addr < vdev->rom_size) ? MIN(size, vdev->rom_size - addr) : 0);
+    if (addr < vdev->rom_size) {
+        memcpy(&val, vdev->rom + addr, MIN(size, vdev->rom_size - addr));
+    }
 
     switch (size) {
     case 1: