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Fri, 5 Feb 2021 07:14:13 +0000 (GMT) Received: from oc7455500831.ibm.com (unknown [9.171.76.67]) by d06av25.portsmouth.uk.ibm.com (Postfix) with ESMTP; Fri, 5 Feb 2021 07:14:13 +0000 (GMT) Subject: Re: [PATCH v2] target/s390x/arch_dump: Fixes for the name field in the PT_NOTE section From: Christian Borntraeger To: Thomas Huth , 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> Message-ID: <896eb62a-19f6-997a-6f38-a10c4b62035a@de.ibm.com> Date: Fri, 5 Feb 2021 08:14:13 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.6.1 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US X-TM-AS-GCONF: 00 Content-Transfer-Encoding: 8bit X-Proofpoint-UnRewURL: 0 URL was un-rewritten MIME-Version: 1.0 X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.369, 18.0.737 definitions=2021-02-05_04:2021-02-05, 2021-02-05 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 adultscore=0 mlxlogscore=999 priorityscore=1501 clxscore=1015 malwarescore=0 bulkscore=0 impostorscore=0 mlxscore=0 suspectscore=0 lowpriorityscore=0 spamscore=0 phishscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2009150000 definitions=main-2102050045 Received-SPF: pass client-ip=148.163.156.1; envelope-from=borntraeger@de.ibm.com; helo=mx0a-001b2d01.pphosted.com X-Spam_score_int: -28 X-Spam_score: -2.9 X-Spam_bar: -- X-Spam_report: (-2.9 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-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=ham 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 05.02.21 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. FWIW, readelf also complains: Displaying notes found at file offset 0x000000b0 with length 0x000004d8: Owner Data size Description CORE 0x00000150 NT_PRSTATUS (prstatus structure) (NONE) 0x00000004 Unknown note type: (0x00000088) description data: 00 00 00 02 readelf: dump.mem2: Warning: note with invalid namesz and/or descsz found at offset 0x170 readelf: dump.mem2: Warning: type: 0x0, namesize: 0x434f5245, descsize: 0x00000000, alignment: 4