From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mailrelay.tugraz.at (mailrelay.tugraz.at [129.27.2.202]) by sourceware.org (Postfix) with ESMTPS id 9BE753858426 for ; Thu, 6 Jul 2023 21:11:00 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.2 sourceware.org 9BE753858426 Authentication-Results: sourceware.org; dmarc=pass (p=quarantine dis=none) header.from=tugraz.at Authentication-Results: sourceware.org; spf=pass smtp.mailfrom=tugraz.at Received: from [192.168.0.221] (84-115-220-241.cable.dynamic.surfer.at [84.115.220.241]) by mailrelay.tugraz.at (Postfix) with ESMTPSA id 4Qxq254LJZz1LM0S; Thu, 6 Jul 2023 23:10:53 +0200 (CEST) DKIM-Filter: OpenDKIM Filter v2.11.0 mailrelay.tugraz.at 4Qxq254LJZz1LM0S DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=tugraz.at; s=mailrelay; t=1688677855; bh=Fa3KY3bhu26bHOpGfvkhOSSZfOJAjRh3wj+TtkWZEDY=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=RvWisVkVoTyGCdQohMz1i319jOw8Dv7WWi6nZ6soW0VzAyUiCI8wzY4zmd3dgoF3P U5mkPnSEvM3ls4YDa3DAO00zvKoSh/NaXYLSP6cW5XrJH28RnSYB2HN4mpQiaVwcBQ 3Pa1L6ivINJc429c23NyoSR1uYHQlxAWZGxk6mnM= Message-ID: <848196d4808cb2293b216d9cbffafa409f70e462.camel@tugraz.at> Subject: Re: [V1][PATCH 0/3] New attribute "element_count" to annotate bounds for C99 FAM(PR108896) From: Martin Uecker To: Qing Zhao , Kees Cook Cc: "joseph@codesourcery.com" , "richard.guenther@gmail.com" , "jakub@redhat.com" , "gcc-patches@gcc.gnu.org" , "siddhesh@gotplt.org" , "isanbard@gmail.com" Date: Thu, 06 Jul 2023 23:10:53 +0200 In-Reply-To: References: <20230525161450.3704901-1-qing.zhao@oracle.com> <202305261218.2420AB8E0@keescook> Content-Type: text/plain; charset="UTF-8" User-Agent: Evolution 3.38.3-1+deb11u2 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-TUG-Backscatter-control: G/VXY7/6zeyuAY/PU2/0qw X-Spam-Scanner: SpamAssassin 3.003001 X-Spam-Score-relay: -0.4 X-Scanned-By: MIMEDefang 2.74 on 129.27.10.117 X-Spam-Status: No, score=-2.8 required=5.0 tests=BAYES_00,BODY_8BITS,DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,KAM_SHORT,RCVD_IN_MSPIKE_H3,RCVD_IN_MSPIKE_WL,SPF_HELO_NONE,SPF_PASS,TXREP,T_SCC_BODY_TEXT_LINE autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org List-Id: Am Donnerstag, dem 06.07.2023 um 18:56 +0000 schrieb Qing Zhao: > Hi, Kees, > > I have updated my V1 patch with the following changes: > A. changed the name to "counted_by" > B. changed the argument from a string to an identifier > C. updated the documentation and testing cases accordingly. > > And then used this new gcc to test https://github.com/kees/kernel-tools/blob/trunk/fortify/array-bounds.c (with the following change) > [opc@qinzhao-ol8u3-x86 Kees]$ !1091 > diff array-bounds.c array-bounds.c.org > 32c32 > < # define __counted_by(member) __attribute__((counted_by (member))) > --- > > # define __counted_by(member) __attribute__((__element_count__(#member))) > 34c34 > < # define __counted_by(member) __attribute__((counted_by (member))) > --- > > # define __counted_by(member) /* __attribute__((__element_count__(#member))) */ > > Then I got the following result: > [opc@qinzhao-ol8u3-x86 Kees]$ ./array-bounds 2>&1 | grep -v ^'#' > TAP version 13 > 1..12 > ok 1 global.fixed_size_seen_by_bdos > ok 2 global.fixed_size_enforced_by_sanitizer > not ok 3 global.unknown_size_unknown_to_bdos > not ok 4 global.unknown_size_ignored_by_sanitizer > ok 5 global.alloc_size_seen_by_bdos > ok 6 global.alloc_size_enforced_by_sanitizer > not ok 7 global.element_count_seen_by_bdos > ok 8 global.element_count_enforced_by_sanitizer > not ok 9 global.alloc_size_with_smaller_element_count_seen_by_bdos > not ok 10 global.alloc_size_with_smaller_element_count_enforced_by_sanitizer > ok 11 global.alloc_size_with_bigger_element_count_seen_by_bdos > ok 12 global.alloc_size_with_bigger_element_count_enforced_by_sanitizer > > The same as your previous results. Then I took a look at all the failed testing: 3, 4, 7, 9, and 10. And studied the reasons for all of them. > >  in a summary, there are two major issues: > 1. The reason for the failed testing 7 is the same issue as I observed in https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109557 > Which is not a bug, it’s an expected behavior. > > 2. The common issue for the failed testing 3, 4, 9, 10 is: > > for the following annotated structure: > > ==== > struct annotated { >         unsigned long flags; >         size_t foo; >         int array[] __attribute__((counted_by (foo))); > }; > > > struct annotated *p; > int index = 16; > > p = malloc(sizeof(*p) + index * sizeof(*p->array)); // allocated real size > > p->foo = index + 2; // p->foo was set by a different value than the real size of p->array as in test 9 and 10 > or > p->foo was not set to any value as in test 3 and 4 > > ==== > > i.e, the value of p->foo is NOT synced with the number of elements allocated for the array p->array. > > I think that this should be considered as an user error, and the documentation of the attribute should include > this requirement. (In the LLVM’s RFC, such requirement was included in the programing model: > https://discourse.llvm.org/t/rfc-enforcing-bounds-safety-in-c-fbounds-safety/70854#maintaining-correctness-of-bounds-annotations-18) > > We can add a new warning option -Wcounted-by to report such user error if needed. > > What’s your opinion on this? Additionally, we could also have a sanitizer that checks this at run-time. Personally, I am still not very happy that in the following example the two 'n's refer to different entities: void f(int n) { struct foo { int n; int (*p[])[n] [[counted_by(n)]]; }; } But I guess it will be difficult to convince everybody that it would be wise to use a new syntax for disambiguation: void f(int n) { struct foo { int n; int (*p[])[n] [[counted_by(.n)]]; }; } Martin > > thanks. > > Qing > > > > On May 26, 2023, at 4:40 PM, Kees Cook wrote: > > > > On Thu, May 25, 2023 at 04:14:47PM +0000, Qing Zhao wrote: > > > GCC will pass the number of elements info from the attached attribute to both > > > __builtin_dynamic_object_size and bounds sanitizer to check the out-of-bounds > > > or dynamic object size issues during runtime for flexible array members. > > > > > > This new feature will provide nice protection to flexible array members (which > > > currently are completely ignored by both __builtin_dynamic_object_size and > > > bounds sanitizers). > > > > Testing went pretty well, though I think I found some bdos issues: > > > > - some things that bdos can't know the size of, and correctly returned > >  SIZE_MAX in the past, now thinks are 0-sized. > > - while bdos correctly knows the size of an element_count-annotated > >  flexible array, it doesn't know the size of the containing object > >  (i.e. it returns SIZE_MAX). > > > > Also, I think I found a precedence issue: > > > > - if both __alloc_size and 'element_count' are in use, the _smallest_ > >  of the two is what I would expect to be enforced by the sanitizer > >  and reported by __bdos. As is, alloc_size appears to be used when > >  it is available, regardless of what 'element_count' shows. > > > > I've updated my test cases to show it more clearly, but here is the > > before/after: > > > > > > GCC 13 (correctly does not implement "element_count"): > > > > $ ./array-bounds 2>&1 | grep -v ^'#' > > TAP version 13 > > 1..12 > > ok 1 global.fixed_size_seen_by_bdos > > ok 2 global.fixed_size_enforced_by_sanitizer > > ok 3 global.unknown_size_unknown_to_bdos > > ok 4 global.unknown_size_ignored_by_sanitizer > > ok 5 global.alloc_size_seen_by_bdos > > ok 6 global.alloc_size_enforced_by_sanitizer > > not ok 7 global.element_count_seen_by_bdos > > not ok 8 global.element_count_enforced_by_sanitizer > > not ok 9 global.alloc_size_with_smaller_element_count_seen_by_bdos > > not ok 10 global.alloc_size_with_smaller_element_count_enforced_by_sanitizer > > ok 11 global.alloc_size_with_bigger_element_count_seen_by_bdos > > ok 12 global.alloc_size_with_bigger_element_count_enforced_by_sanitizer > > > > > > ToT GCC + this element_count series: > > > > $ ./array-bounds 2>&1 | grep -v ^'#' > > TAP version 13 > > 1..12 > > ok 1 global.fixed_size_seen_by_bdos > > ok 2 global.fixed_size_enforced_by_sanitizer > > not ok 3 global.unknown_size_unknown_to_bdos > > not ok 4 global.unknown_size_ignored_by_sanitizer > > ok 5 global.alloc_size_seen_by_bdos > > ok 6 global.alloc_size_enforced_by_sanitizer > > not ok 7 global.element_count_seen_by_bdos > > ok 8 global.element_count_enforced_by_sanitizer > > not ok 9 global.alloc_size_with_smaller_element_count_seen_by_bdos > > not ok 10 global.alloc_size_with_smaller_element_count_enforced_by_sanitizer > > ok 11 global.alloc_size_with_bigger_element_count_seen_by_bdos > > ok 12 global.alloc_size_with_bigger_element_count_enforced_by_sanitizer > > > > > > Test suite is here: > > https://github.com/kees/kernel-tools/blob/trunk/fortify/array-bounds.c > > > > -- > > Kees Cook >