Allocate static pages in memory strictly MAXALIGNed to avoid overflow

pashkinelfe · pashkinelfe · commit 9e1b4419d5da · 2020-12-11T23:49:25.000+04:00
due to adding padding bytes by Postgres data access alignment macros.
This was the source of rare but dangerous segfault on 32-bit FreeBSD
but no system was safe as static alignment is completely
system/compiler free choice.

This problem was hidden by the added completely unrelated variable
trace_sort way before the relevant part of the code. It just shifted
the alignment of all variables with bigger address values to
acceptable but haven't solved the problem at large.
diff --git a/src/rumdatapage.c b/src/rumdatapage.c
@@ -853,7 +853,14 @@ dataPlaceToPage(RumBtree btree, Page page, OffsetNumber off)
 		ItemPointerData iptr = {{0, 0}, 0};
 		RumItem		copyItem;
 		bool		copyItemEmpty = true;
-		char		pageCopy[BLCKSZ];
+		/*
+		 * Must have pageCopy MAXALIGNed to use PG macros to access data in
+		 * it. Should not rely on compiler alignment preferences to avoid
+		 * pageCopy overflow related to PG in-memory page items alignment
+		 * inside rumDataPageLeafRead() or elsewhere.
+		 */
+		char		pageCopyStorage[BLCKSZ + MAXIMUM_ALIGNOF];
+		char	   *pageCopy = (char *) MAXALIGN(pageCopyStorage);
 		int			maxoff = RumPageGetOpaque(page)->maxoff;
 		int			freespace,
 					insertCount = 0;
@@ -1055,7 +1062,14 @@ dataSplitPageLeaf(RumBtree btree, Buffer lbuf, Buffer rbuf,
 	RumItem		item;
 	int			totalCount = 0;
 	int			maxItemIndex = btree->curitem;
-	static char lpageCopy[BLCKSZ];
+	/*
+	 * Must have lpageCopy MAXALIGNed to use PG macros to access data in
+	 * it. Should not rely on compiler alignment preferences to avoid
+	 * lpageCopy overflow related to PG in-memory page items alignment
+	 * inside rumDataPageLeafRead() etc.
+	 */
+	static char lpageCopyStorage[BLCKSZ + MAXIMUM_ALIGNOF];
+	char 	   *lpageCopy = (char *) MAXALIGN(lpageCopyStorage);
 
 	memset(&item, 0, sizeof(item));
 	dataPrepareData(btree, newlPage, off);
@@ -1233,8 +1247,14 @@ dataSplitPageInternal(RumBtree btree, Buffer lbuf, Buffer rbuf,
 	OffsetNumber maxoff = RumPageGetOpaque(newlPage)->maxoff;
 	Size		pageSize = PageGetPageSize(newlPage);
 	Size		freeSpace;
-
-	static char vector[2 * BLCKSZ];
+	/*
+	 * Must have vector MAXALIGNed to use PG macros to access data in
+	 * it. Should not rely on compiler alignment preferences to avoid
+	 * vector overflow related to PG in-memory page items alignment
+	 * inside rumDataPageLeafRead() etc.
+	 */
+	static char vectorStorage[2 * BLCKSZ + MAXIMUM_ALIGNOF];
+	char 	   *vector = (char *) MAXALIGN(vectorStorage);
 
 	RumInitPage(rPage, RumPageGetOpaque(newlPage)->flags, pageSize);
 	freeSpace = RumDataPageGetFreeSpace(rPage);
diff --git a/src/rumentrypage.c b/src/rumentrypage.c
@@ -428,8 +428,14 @@ entrySplitPage(RumBtree btree, Buffer lbuf, Buffer rbuf,
 	Page		page;
 	Page		newlPage = PageGetTempPageCopy(lPage);
 	Size		pageSize = PageGetPageSize(newlPage);
-
-	static char tupstore[2 * BLCKSZ];
+	/*
+	 * Must have tupstore MAXALIGNed to use PG macros to access data in
+	 * it. Should not rely on compiler alignment preferences to avoid
+	 * tupstore overflow related to PG in-memory page items alignment
+	 * inside rumDataPageLeafRead() or elsewhere.
+	 */
+	static char tupstoreStorage[2 * BLCKSZ + MAXIMUM_ALIGNOF];
+	char 	   *tupstore = (char *) MAXALIGN(tupstoreStorage);
 
 	entryPreparePage(btree, newlPage, off);
 
