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Thu, 4 Feb 2021 13:01:48 +0000 (GMT) Received: from oc7455500831.ibm.com (unknown [9.171.45.97]) by b06wcsmtp001.portsmouth.uk.ibm.com (Postfix) with ESMTP; Thu, 4 Feb 2021 13:01:48 +0000 (GMT) Subject: Re: [PATCH] target/s390x/arch_dump: Fixes for the name field in the PT_NOTE section To: Thomas Huth , qemu-devel@nongnu.org, Cornelia Huck References: <20210203094454.260583-1-thuth@redhat.com> From: Christian Borntraeger Message-ID: <1edf8bcd-3001-d459-3283-20e8ae2a3862@de.ibm.com> Date: Thu, 4 Feb 2021 14:01:48 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.6.1 In-Reply-To: <20210203094454.260583-1-thuth@redhat.com> 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=2021-02-04_06:2021-02-04, 2021-02-04 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 bulkscore=0 suspectscore=0 impostorscore=0 mlxscore=0 phishscore=0 priorityscore=1501 clxscore=1015 spamscore=0 lowpriorityscore=0 malwarescore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2009150000 definitions=main-2102040077 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=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 03.02.21 10:44, 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, we can simply decrease > the size of the strncpy by one here 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 > --- > The ELF-64 spec can be found here, for example: > https://uclibc.org/docs/elf-64-gen.pdf > > Here's a CI run with the compiler warning: > https://gitlab.com/huth/qemu/-/jobs/1003508341#L1248 > > target/s390x/arch_dump.c | 6 ++++-- > 1 file changed, 4 insertions(+), 2 deletions(-) > > diff --git a/target/s390x/arch_dump.c b/target/s390x/arch_dump.c > index 50fa0ae4b6..20c3a09707 100644 > --- a/target/s390x/arch_dump.c > +++ b/target/s390x/arch_dump.c > @@ -212,11 +212,13 @@ static int s390x_write_elf64_notes(const char *note_name, > int note_size; > int ret = -1; > > + assert(strlen(note_name) < sizeof(note.name)); > + > for (nf = funcs; nf->note_contents_func; nf++) { > memset(¬e, 0, sizeof(note)); > - note.hdr.n_namesz = cpu_to_be32(strlen(note_name) + 1); > + note.hdr.n_namesz = cpu_to_be32(strlen(note_name)); > note.hdr.n_descsz = cpu_to_be32(nf->contents_size); > - strncpy(note.name, note_name, sizeof(note.name)); > + strncpy(note.name, note_name, sizeof(note.name) - 1); This kind of feels wrong. With 8 bytes of note.name, we should be able to store "Test123" + the final \0. Now we tell strncpy to stop at 7. Which means that for Test123 we would NOT copy the final \0. So I actually think that the sanitize warning is wrong (as long as the assertion holds true).