diff -urN harfbuzz-1.7.5.old/src/hb-ot-layout-gsubgpos-private.hh harfbuzz-1.7.5/src/hb-ot-layout-gsubgpos-private.hh
--- harfbuzz-1.7.5.old/src/hb-ot-layout-gsubgpos-private.hh	2018-01-27 07:43:07.000000000 +0530
+++ harfbuzz-1.7.5/src/hb-ot-layout-gsubgpos-private.hh	2023-09-25 12:18:00.277228938 +0530
@@ -368,7 +368,15 @@
     inline bool prev (void)
     {
       assert (num_items > 0);
-      while (idx >= num_items)
+      unsigned stop = num_items - 1;
+
+      /* When looking back, limit how far we search; this function is mostly
+       * used for looking back for base glyphs when attaching marks. If we
+       * don't limit, we can get O(n^2) behavior where n is the number of
+       * consecutive marks. */
+      stop = (unsigned) ((int) stop >= (int) idx - HB_MAX_CONTEXT_LENGTH ? stop : (int) idx - HB_MAX_CONTEXT_LENGTH);
+
+      while (idx > stop)
       {
 	idx--;
 	const hb_glyph_info_t &info = c->buffer->out_info[idx];