edu: fix DMA range upper bound check

The edu_check_range function checks that start <= end1 < end2, where
end1 is the upper bound (exclusive) of the guest-supplied DMA range and
end2 is the upper bound (exclusive) of the device's allowed DMA range.
When the guest tries to transfer exactly DMA_SIZE (4096) bytes, end1
will be equal to end2, so the check fails and QEMU aborts with this
puzzling error message (newlines added for formatting):

  qemu: hardware error: EDU: DMA range
    0x0000000000040000-0x0000000000040fff out of bounds
   (0x0000000000040000-0x0000000000040fff)!

By checking end1 <= end2 instead, guests will be allowed to transfer
exactly 4096 bytes. It is not necessary to explicitly check for
start <= end1 because the previous two checks (within(addr, start, end2)
and end1 > addr) imply start < end1.

Fixes: b30934cb52a7 ("hw: misc, add educational driver", 2015-01-21)
Signed-off-by: Max Erenberg <merenber@uwaterloo.ca>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>

diff --git a/hw/misc/edu.c b/hw/misc/edu.c
index a1f8bc77e7701eb90abab3faef46164503e39560..e64a246d3febf9c096c27cb299b83d6fa1a0477d 100644 (file)
--- a/hw/misc/edu.c
+++ b/hw/misc/edu.c
@@ -115,7 +115,7 @@ static void edu_check_range(uint64_t addr, uint64_t size1, uint64_t start,
     uint64_t end2 = start + size2;
 
     if (within(addr, start, end2) &&
-            end1 > addr && within(end1, start, end2)) {
+            end1 > addr && end1 <= end2) {
         return;
     }