[Qemu-devel] [PATCH v2] exec: Fix non-power-of-2 sized accesses

[Alex Williamson <alex.williamson@redhat.com>]

Since commit 23326164 we align access sizes to match the alignment of
the address, but we don't align the access size itself.  This means we
let illegal access sizes (ex. 3) slip through if the address is
sufficiently aligned (ex. 4).  This results in an abort which would be
easy for a guest to trigger.  Account for aligning the access size.

Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
Cc: qemu-stable@nongnu.org
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
---

v2: Remove unnecessary loop condition

 exec.c |    7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/exec.c b/exec.c
index 3ca9381..3c19147 100644
--- a/exec.c
+++ b/exec.c
@@ -1924,6 +1924,13 @@ static int memory_access_size(MemoryRegion *mr, unsigned l, hwaddr addr)
         }
     }
 
+    /* Size must be a power of 2 */
+    if (l & (l - 1)) {
+        while (l & (access_size_max - 1)) {
+            access_size_max >>= 1;
+        }
+    }
+
     /* Don't attempt accesses larger than the maximum.  */
     if (l > access_size_max) {
         l = access_size_max;