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 3336FCE7A89 for ; Sun, 24 Sep 2023 00:53:54 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229785AbjIXAx6 (ORCPT ); Sat, 23 Sep 2023 20:53:58 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44156 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229450AbjIXAx4 (ORCPT ); Sat, 23 Sep 2023 20:53:56 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C5288192 for ; Sat, 23 Sep 2023 17:53:04 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1695516783; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=DTFrEa7vKTqj7wXo0iZDISbSz3Y6un7zOPt1IkyamfI=; b=C6G2RxUdp5vp/wVHNg5Z0rPoDTlaT5oSn7mzm8Og1fDUy5BUX0jr2wN/pezFJKVKmQQx74 Oz+63z18ZZLaURVvMwJ3vlvy2oyGNMvU+pbz/Kq2WbLzGDV3Bm3y1VSdQavk32wI5al1us MhXwi9TUsGYd0LEg88VCEzZPDAeUgTg= Received: from mimecast-mx02.redhat.com (mx-ext.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-67-sP602GgzNLKaiZQK_BLycg-1; Sat, 23 Sep 2023 20:53:00 -0400 X-MC-Unique: sP602GgzNLKaiZQK_BLycg-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.rdu2.redhat.com [10.11.54.6]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id A7FC43806712; Sun, 24 Sep 2023 00:52:59 +0000 (UTC) Received: from localhost (unknown [10.72.112.26]) by smtp.corp.redhat.com (Postfix) with ESMTPS id D4E512156701; Sun, 24 Sep 2023 00:52:58 +0000 (UTC) Date: Sun, 24 Sep 2023 08:52:55 +0800 From: Baoquan He To: Kees Cook Cc: Eric Biederman , kexec@lists.infradead.org, Vivek Goyal , Dave Young , Nathan Chancellor , Nick Desaulniers , Tom Rix , linux-kernel@vger.kernel.org, llvm@lists.linux.dev, linux-hardening@vger.kernel.org, Shakeel Butt Subject: Re: [PATCH] kexec: Annotate struct crash_mem with __counted_by Message-ID: References: <20230922175224.work.712-kees@kernel.org> <202309222012.49E3C0AA@keescook> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <202309222012.49E3C0AA@keescook> X-Scanned-By: MIMEDefang 3.1 on 10.11.54.6 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 09/22/23 at 08:25pm, Kees Cook wrote: > On Sat, Sep 23, 2023 at 08:46:47AM +0800, Baoquan He wrote: > > On 09/22/23 at 10:52am, Kees Cook wrote: > > > Prepare for the coming implementation by GCC and Clang of the __counted_by > > > attribute. Flexible array members annotated with __counted_by can have > > > their accesses bounds-checked at run-time checking via CONFIG_UBSAN_BOUNDS > > > (for array indexing) and CONFIG_FORTIFY_SOURCE (for strcpy/memcpy-family > > > functions). > > > > > > As found with Coccinelle[1], add __counted_by for struct crash_mem. > > > > > > [1] https://github.com/kees/kernel-tools/blob/trunk/coccinelle/examples/counted_by.cocci > > > > > > Cc: Eric Biederman > > > Cc: kexec@lists.infradead.org > > > Signed-off-by: Kees Cook > > > --- > > > include/linux/crash_core.h | 2 +- > > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > > > diff --git a/include/linux/crash_core.h b/include/linux/crash_core.h > > > index 3426f6eef60b..5126a4fecb44 100644 > > > --- a/include/linux/crash_core.h > > > +++ b/include/linux/crash_core.h > > > @@ -131,7 +131,7 @@ static inline void __init reserve_crashkernel_generic(char *cmdline, > > > struct crash_mem { > > > unsigned int max_nr_ranges; > > > unsigned int nr_ranges; > > > - struct range ranges[]; > > > + struct range ranges[] __counted_by(max_nr_ranges); > > > > This __counted_by() only makes sense when there's a obvious upper > > boundary, max_nr_ranges in this case. > > Yes; it's designed to be the array element count used for the > allocation. For example with the above case: > > nr_ranges += 2; > cmem = vzalloc(struct_size(cmem, ranges, nr_ranges)); > if (!cmem) > return NULL; > > cmem->max_nr_ranges = nr_ranges; > cmem->nr_ranges = 0; > > nr_ranges is the max count of the elements. > > _However_, if a structure (like this one) has _two_ counters, one for > "in use" and another for "max available", __counted_by could specify the > "in use" case, as long as array indexing only happens when that "in use" > has been updated. So, if it were: > > struct crash_mem { > unsigned int max_nr_ranges; > unsigned int nr_ranges; > struct range ranges[] __counted_by(nr_ranges); > }; > > then this would trigger the bounds checking: > > cmem->ranges[0] = some_range; /* "nr_ranges" is still 0 so index 0 isn't allowed */ > cmem->nr_ranges ++; > > but this would not: > > cmem->nr_ranges ++; /* index 0 is now available for use. */ > cmem->ranges[0] = some_range; > > > This heavily depends and isn't much in kernel? > > Which "this" do you mean? The tracking of max allocation is common. > Tracking max and "in use" happens in some places (like here), but is > less common. I thought usually it may not have a max counter of the variable length array embeded in struct, seems I was wrong. Here 'this' means the __counted_by() adding for the variable length array. > > > E.g struct swap_info_struct->avail_lists[]. > > This is even less common: tracking the count externally from the struct, > as done there with nr_node_ids. Shakeel asked a very similar question > and also pointed out nr_node_ids: > https://lore.kernel.org/all/202309221128.6AC35E3@keescook/ > > > Just curious, not related to this patch though. > > I'm happy to answer questions! Yeah, as I said in the above thread, > I expect to expand what __counted_by can use, and I suspect (hope) > a global would be easier to add than an arbitrary expression. :) Thanks a lot for these explanation, Kees. LGTM, Acked-by: Baoquan He