sna: Catch SIGBUS to prevent X death

We know that when we access either a CPU or GTT mmap we are vulernable
to receiving a SIGBUS. In fact, we can catch these and abort the
operation preventing X and all of its clients from randomly dieing.

This helps for instance if you try and use a 1GiB frontbuffer on a 2GiB
machine...

For complete protection, we also need to catch signals for all GTT maps,
such as VBO and staging buffers. (TBD)

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

1 files changed, 16 insertions, 10 deletions

diff --git a/src/sna/sna_render.c b/src/sna/sna_render.c
index 84275c43..73d53ba7 100644
--- a/src/sna/sna_render.c
+++ b/src/sna/sna_render.c
@@ -1676,11 +1676,14 @@ do_fixup:
 
 	DBG(("%s: compositing tmp=(%d+%d, %d+%d)x(%d, %d)\n",
 	     __FUNCTION__, x, dx, y, dy, w, h));
-	sna_image_composite(PictOpSrc, src, NULL, dst,
-			    x + dx, y + dy,
-			    0, 0,
-			    0, 0,
-			    w, h);
+	if (sigtrap_get() == 0) {
+		sna_image_composite(PictOpSrc, src, NULL, dst,
+				    x + dx, y + dy,
+				    0, 0,
+				    0, 0,
+				    w, h);
+		sigtrap_put();
+	}
 	free_pixman_pict(picture, src);
 
 	/* Then convert to card format */
@@ -1883,11 +1886,14 @@ sna_render_picture_convert(struct sna *sna,
 			return 0;
 		}
 
-		pixman_image_composite(PictOpSrc, src, NULL, dst,
-				       box.x1, box.y1,
-				       0, 0,
-				       0, 0,
-				       w, h);
+		if (sigtrap_get() == 0) {
+			pixman_image_composite(PictOpSrc, src, NULL, dst,
+					       box.x1, box.y1,
+					       0, 0,
+					       0, 0,
+					       w, h);
+			sigtrap_put();
+		}
 		pixman_image_unref(dst);
 		pixman_image_unref(src);
 	}