Index: head/sys/kern/imgact_elf.c
===================================================================
--- head/sys/kern/imgact_elf.c
+++ head/sys/kern/imgact_elf.c
@@ -1160,7 +1160,7 @@
 
 static void cb_put_phdr(vm_map_entry_t, void *);
 static void cb_size_segment(vm_map_entry_t, void *);
-static int core_write(struct coredump_params *, void *, size_t, off_t,
+static int core_write(struct coredump_params *, const void *, size_t, off_t,
     enum uio_seg);
 static void each_dumpable_segment(struct thread *, segment_callback, void *);
 static int __elfN(corehdr)(struct coredump_params *, int, void *, size_t,
@@ -1202,7 +1202,14 @@
 
 	while (len > 0) {
 		chunk_len = MIN(len, CORE_BUF_SIZE);
-		copyin(base, buf, chunk_len);
+
+		/*
+		 * We can get EFAULT error here.
+		 * In that case zero out the current chunk of the segment.
+		 */
+		error = copyin(base, buf, chunk_len);
+		if (error != 0)
+			bzero(buf, chunk_len);
 		error = gzio_write(p->gzs, buf, chunk_len);
 		if (error != 0)
 			break;
@@ -1222,12 +1229,12 @@
 #endif /* GZIO */
 
 static int
-core_write(struct coredump_params *p, void *base, size_t len, off_t offset,
-    enum uio_seg seg)
+core_write(struct coredump_params *p, const void *base, size_t len,
+    off_t offset, enum uio_seg seg)
 {
 
-	return (vn_rdwr_inchunks(UIO_WRITE, p->vp, base, len, offset,
-	    seg, IO_UNIT | IO_DIRECT | IO_RANGELOCKED,
+	return (vn_rdwr_inchunks(UIO_WRITE, p->vp, __DECONST(void *, base),
+	    len, offset, seg, IO_UNIT | IO_DIRECT | IO_RANGELOCKED,
 	    p->active_cred, p->file_cred, NULL, p->td));
 }
 
@@ -1235,12 +1242,32 @@
 core_output(void *base, size_t len, off_t offset, struct coredump_params *p,
     void *tmpbuf)
 {
+	int error;
 
 #ifdef GZIO
 	if (p->gzs != NULL)
 		return (compress_chunk(p, base, tmpbuf, len));
 #endif
-	return (core_write(p, base, len, offset, UIO_USERSPACE));
+	/*
+	 * EFAULT is a non-fatal error that we can get, for example,
+	 * if the segment is backed by a file but extends beyond its
+	 * end.
+	 */
+	error = core_write(p, base, len, offset, UIO_USERSPACE);
+	if (error == EFAULT) {
+		log(LOG_WARNING, "Failed to fully fault in a core file segment "
+		    "at VA %p with size 0x%zx to be written at offset 0x%jx "
+		    "for process %s\n", base, len, offset, curproc->p_comm);
+
+		/*
+		 * Write a "real" zero byte at the end of the target region
+		 * in the case this is the last segment.
+		 * The intermediate space will be implicitly zero-filled.
+		 */
+		error = core_write(p, zero_region, 1, offset + len - 1,
+		    UIO_SYSSPACE);
+	}
+	return (error);
 }
 
 /*