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bh=Tz1oBnK7tUuAotTyXd228IM4OrV4j6mwhWfXBfvZwTA=; b=dXYGyfXVPLRGPFFW1ApnE97DmLcNRZzvCecGKAoAe6GWXYt8NjEXtow1MT54MEpVaweYF+ endHHjsryM/L7O9NUM3s8wnhBsTYuo7jjBKVIlMkOnJA2QW3E+BGSG/YSauiuCYqRoaSen H6gkHMqo7RwAqYYSnu07TzLnZtHknsU= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-571-CU8PcwAJPIiC3Qb3uw2k-A-1; Fri, 05 Feb 2021 03:18:25 -0500 X-MC-Unique: CU8PcwAJPIiC3Qb3uw2k-A-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id D422C1020C3E; Fri, 5 Feb 2021 08:18:23 +0000 (UTC) Received: from thuth.remote.csb (ovpn-112-46.ams2.redhat.com [10.36.112.46]) by smtp.corp.redhat.com (Postfix) with ESMTP id E4F025D9D3; Fri, 5 Feb 2021 08:18:18 +0000 (UTC) Subject: Re: [PATCH v2] target/s390x/arch_dump: Fixes for the name field in the PT_NOTE section To: Christian Borntraeger , qemu-devel@nongnu.org, Cornelia Huck References: <20210204164117.721110-1-thuth@redhat.com> <8674a570-93f7-24dc-10b8-0c3577c0841f@de.ibm.com> <1d54bafb-b995-0052-e9f9-2572e69dcc11@redhat.com> From: Thomas Huth Message-ID: <79f2abd2-fe71-006f-d9b4-a3781f292766@redhat.com> Date: Fri, 5 Feb 2021 09:18:17 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.7.0 MIME-Version: 1.0 In-Reply-To: X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=thuth@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=216.205.24.124; envelope-from=thuth@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -32 X-Spam_score: -3.3 X-Spam_bar: --- X-Spam_report: (-3.3 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.351, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-0.182, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=unavailable autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: qemu-s390x@nongnu.org, Richard Henderson , David Hildenbrand Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 05/02/2021 08.08, Christian Borntraeger wrote: > > > On 05.02.21 07:12, Thomas Huth wrote: >> On 04/02/2021 18.00, Christian Borntraeger wrote: >>> On 04.02.21 17:41, Thomas Huth wrote: >>>> According to the "ELF-64 Object File Format" specification: >>>> >>>> "The first word in the entry, namesz, identifies the length, in >>>>   bytes, of a name identifying the entry’s owner or originator. The name field >>>>   contains a null-terminated string, with padding as necessary to ensure 8- >>>>   byte alignment for the descriptor field. The length does not include the >>>>   terminating null or the padding." >>>> >>>> So we should not include the terminating NUL in the length field here. >>>> >>>> Also there is a compiler warning with GCC 9.3 when compiling with >>>> the -fsanitize=thread compiler flag: >>>> >>>>   In function 'strncpy', >>>>      inlined from 's390x_write_elf64_notes' at ../target/s390x/arch_dump.c:219:9: >>>>   /usr/include/x86_64-linux-gnu/bits/string_fortified.h:106:10: error: >>>>    '__builtin_strncpy' specified bound 8 equals destination size >>>>    [-Werror=stringop-truncation] >>>> >>>> Since the name should always be NUL-terminated, let's use g_strlcpy() to >>>> silence this warning. And while we're at it, also add an assert() to make >>>> sure that the provided names always fit the size field (which is fine for >>>> the current callers, the function is called once with "CORE" and once with >>>> "LINUX" as a name). >>>> >>>> Signed-off-by: Thomas Huth >>>> --- >>>>   v2: Use g_strlcpy instead of strncpy >>> >>> >>> With this patch I do get >>> >>> WARNING: possibly corrupt Elf64_Nhdr: n_namesz: 0 n_descsz: 4 n_type: 88 >>> >>> when running crash on the elf file created by dump-guest-memory. Without the >>> patch everything is fine. >> >> Drat! Looking at the crash sources: >> >>  https://github.com/crash-utility/crash/blob/master/s390x.c#L378 >> >> ... it seems like crash is rather rounding up to the next 4 bytes boundary instead of the next 8 bytes boundary. Thus things go wrong now when QEMU writes writes the "CORE" notes section. In the old code we were using 4 + 1 as a lengths, so crash correctly rounded this up to 8. But now with 4 as a length, this does not work right anymore :-( >> >> Seems like I either misunderstood the "ELF-64 Object File Format" specification, or this is a bug in the crash utility (it should either add 1 to n_namesz for the trailing NUL or pad to 8 instead of 4)? Anyway, it's maybe better to keep the "+ 1" in QEMU for now to avoid breaking things, I guess? > > I guess kdump and friends are also doing the +1 otherwise we would see the error with those ELF dumps. > But yes, as long as crash does not work we must not apply this patch. Looking at the other target/*/arch_dump.c files, it also seems like they include the NUL in the namesz field for their 64-bit flavours ... I've got the feeling that the "ELF-64 Object File Format" spec simply does not apply here, or I must have missed something else. Big sorry for the noise, I should have tested this more thoroughly before sending out the patch! I'll respin with just the change to strncpy instead... Thomas