From mboxrd@z Thu Jan 1 00:00:00 1970 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 8B258C0015E for ; Thu, 20 Jul 2023 16:25:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230346AbjGTQZw (ORCPT ); Thu, 20 Jul 2023 12:25:52 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51784 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230194AbjGTQZs (ORCPT ); Thu, 20 Jul 2023 12:25:48 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id DAFCF9E for ; Thu, 20 Jul 2023 09:25:47 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 7844861A6D for ; Thu, 20 Jul 2023 16:25:47 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id F3442C433CD; Thu, 20 Jul 2023 16:25:44 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1689870346; bh=e2loJuE/ZqGkDkAvmTjMFKYb1nNFlu5Zk7Uq4LKqs3k=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=D3aC6zTL+n3FzJVGA/KDjcpv5j9Cuw7yM8SijVK45May6Dy/gYCHzCkgQUrLoNL0N 75GyriGucZM+2PJSJ4U8/C535c5T/RdNo0MsKYUoGD8fs5v0a79M7aN3MYP3fl3FWf PQ6WY/ediXDPQksW6rcqLv/XBSywTgj18AqBwQwVjiByVxuZiHRXjndGRDtHyVDfy6 O1ceM8q4TKDFQkXJ1D9E0wbwD+t4bKZqqtUWTZAZhND8G5wJ3duYhy2WYR4o7kds4H RSlHZuPHuRWDozx8FEiMwAd7WawvsR+sfoVUppFFCGGOi+SHg+b8bg1IKI4cGUT9DA UQQxwfXv/WpTA== Date: Thu, 20 Jul 2023 19:25:22 +0300 From: Mike Rapoport To: Rik van Riel Cc: Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-team@meta.com Subject: Re: [PATCH] mm,memblock: reset memblock.reserved to system init state to prevent UAF Message-ID: <20230720162522.GO1901145@kernel.org> References: <20230719154137.732d8525@imladris.surriel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230719154137.732d8525@imladris.surriel.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jul 19, 2023 at 03:41:37PM -0400, Rik van Riel wrote: > 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. I'm going to apply this with the last paragraph rewritten as If memblock_free is called after memblock memory is discarded, 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 = memblock_reserved_init_regions; > + memblock.reserved.cnt = 1; > + memblock_remove_region(&memblock.reserved, 0); > } > > if (memblock.memory.regions != memblock_memory_init_regions) { > -- > 2.34.1 > > -- Sincerely yours, Mike.