[PATCH v4 1/3] hw: misc: edu: fix 2 off-by-one errors

[Chris Friedt <chrisfriedt@gmail.com>]

In the case that size1 was zero, because of the explicit
'end1 > addr' check, the range check would fail and the error
message would read as shown below. The correct comparison
is 'end1 >= addr'.

EDU: DMA range 0x40000-0x3ffff out of bounds (0x40000-0x40fff)!

At the opposite end, in the case that size1 was 4096, within()
would fail because of the non-inclusive check 'end1 < end2',
which should have been 'end1 <= end2'. The error message would
previously say

EDU: DMA range 0x40000-0x40fff out of bounds (0x40000-0x40fff)!

Signed-off-by: Chris Friedt <cfriedt@meta.com>
---
 hw/misc/edu.c | 17 ++++++++---------
 1 file changed, 8 insertions(+), 9 deletions(-)

diff --git a/hw/misc/edu.c b/hw/misc/edu.c
index e935c418d4..b3de8d206a 100644
--- a/hw/misc/edu.c
+++ b/hw/misc/edu.c
@@ -103,19 +103,18 @@ static void edu_lower_irq(EduState *edu, uint32_t val)
     }
 }
 
-static bool within(uint64_t addr, uint64_t start, uint64_t end)
-{
-    return start <= addr && addr < end;
-}
-
-static void edu_check_range(uint64_t addr, uint64_t size1, uint64_t start,
-                uint64_t size2)
+static void edu_check_range(uint64_t addr, uint64_t size1,
+                uint64_t start, uint64_t size2)
 {
     uint64_t end1 = addr + size1;
     uint64_t end2 = start + size2;
 
-    if (within(addr, start, end2) &&
-            end1 > addr && within(end1, start, end2)) {
+    /*
+     * 1. ensure we aren't overflowing
+     * 2. ensure that [addr, end1) is within [start, size2)
+     */
+    if (end2 >= start && end1 >= addr &&
+        addr >= start && end1 <= end2) {
         return;
     }
 
-- 
2.36.1