From nobody Sun Feb 8 05:29:40 2026 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id E7365C001B0 for ; Wed, 19 Jul 2023 19:52:49 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230383AbjGSTws (ORCPT ); Wed, 19 Jul 2023 15:52:48 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40866 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229853AbjGSTwq (ORCPT ); Wed, 19 Jul 2023 15:52:46 -0400 X-Greylist: delayed 654 seconds by postgrey-1.37 at lindbergh.monkeyblade.net; Wed, 19 Jul 2023 12:52:44 PDT Received: from shelob.surriel.com (shelob.surriel.com [96.67.55.147]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id BDD3CA7 for ; Wed, 19 Jul 2023 12:52:44 -0700 (PDT) Received: from [2601:18c:8180:ac39:6e0b:84ff:fee2:98bb] (helo=imladris.surriel.com) by shelob.surriel.com with esmtpsa (TLS1.2) tls TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384 (Exim 4.96) (envelope-from ) id 1qMD3N-0007gS-36; Wed, 19 Jul 2023 15:41:41 -0400 Date: Wed, 19 Jul 2023 15:41:37 -0400 From: Rik van Riel To: Mike Rapoport Cc: Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-team@meta.com Subject: [PATCH] mm,memblock: reset memblock.reserved to system init state to prevent UAF Message-ID: <20230719154137.732d8525@imladris.surriel.com> X-Mailer: Claws Mail 4.1.1 (GTK 3.24.38; x86_64-redhat-linux-gnu) MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Sender: riel@surriel.com Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" The memblock_discard function frees the memblock.reserved.regions array, which is good. However, if a subsequent memblock_free (or memblock_phys_free) comes in later, from for example ima_free_kexec_buffer, that will result in a use after free bug in memblock_isolate_range. When running a kernel with CONFIG_KASAN enabled, this will cause a kernel panic very early in boot. Without CONFIG_KASAN, there is a chance that memblock_isolate_range might scribble on memory that is now in use by somebody else. Avoid those issues by making sure that memblock_discard points memblock.reserved.regions back at the static buffer. If memblock_discard is called while there is still memory in the memblock.reserved type, that will print a warning in memblock_remove_region. Signed-off-by: Rik van Riel --- mm/memblock.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/mm/memblock.c b/mm/memblock.c index 3feafea06ab2..068289a46903 100644 --- a/mm/memblock.c +++ b/mm/memblock.c @@ -374,6 +374,10 @@ void __init memblock_discard(void) kfree(memblock.reserved.regions); else memblock_free_late(addr, size); + /* Reset to prevent UAF from stray frees. */ + memblock.reserved.regions =3D memblock_reserved_init_regions; + memblock.reserved.cnt =3D 1; + memblock_remove_region(&memblock.reserved, 0); } =20 if (memblock.memory.regions !=3D memblock_memory_init_regions) { --=20 2.34.1