Enforce memory mask so 640x350 graphics mode does not cause DOSBox-X …

…to crash when video memory size is less than 256KB
joncampbell123 · Jun 14, 2024 · 7e25d5a · 7e25d5a
1 parent cfb5fa9
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diff --git a/CHANGELOG b/CHANGELOG
@@ -1,4 +1,6 @@
 Next:
+  - Fix memory buffer overrun with machine=ega that can occur with
+    640x350 mode and less than 256KB of video RAM. (joncampbell123).
   - The DOSBox clipboard API (via INT 2Fh) is now disabled by default, because
     some programs use it's presence to detect whether they are running under
     Windows. This fixes a program where Norton Desktop 1.0 does not use it's

diff --git a/src/hardware/vga_draw.cpp b/src/hardware/vga_draw.cpp
@@ -5897,7 +5897,7 @@ static void VGA_VerticalTimer(Bitu /*val*/) {
 			 * switch the CRTC to other non-BYTE modes:
 			 *
 			 * - "Unreal" by Future Crew, "Vectorballs", CRTC WORD mode */
-			vga.draw.linear_mask = 0x3ffffu;
+			vga.draw.linear_mask = 0x3ffffu & vga.mem.memmask; /* NTS: We allow EGA with less than 256KB! */
 			vga.draw.address *= (Bitu)1u << (Bitu)vga.config.addr_shift; /* NTS: Remember the bizarre 4 x 4 mode most SVGA chipsets do */
 			break;
 		case M_VGA: