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Mon, 14 Oct 2024 13:27:03 +0000 (GMT) Received: from smtpav03.dal12v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id AA4A35805A; Mon, 14 Oct 2024 13:27:03 +0000 (GMT) Received: from [9.47.158.152] (unknown [9.47.158.152]) by smtpav03.dal12v.mail.ibm.com (Postfix) with ESMTP; Mon, 14 Oct 2024 13:27:03 +0000 (GMT) Message-ID: Date: Mon, 14 Oct 2024 09:27:03 -0400 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 2/2] tpm_emulator: Read control channel response in 2 passes To: qemu-devel@nongnu.org Cc: berrange@redhat.com, marcandre.lureau@gmail.com References: <20241011223556.2953808-1-stefanb@linux.ibm.com> <20241011223556.2953808-3-stefanb@linux.ibm.com> Content-Language: en-US From: Stefan Berger In-Reply-To: <20241011223556.2953808-3-stefanb@linux.ibm.com> Content-Type: text/plain; charset=UTF-8; format=flowed X-TM-AS-GCONF: 00 X-Proofpoint-ORIG-GUID: E2YhI2yzUtcDcBKqu0WxNEi4zSh1H4L0 X-Proofpoint-GUID: nHpJVW39WP0YGFp5cGMZKE8DdshmZDzk Content-Transfer-Encoding: 7bit X-Proofpoint-UnRewURL: 0 URL was un-rewritten MIME-Version: 1.0 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1051,Hydra:6.0.680,FMLib:17.12.62.30 definitions=2024-10-14_10,2024-10-11_01,2024-09-30_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 malwarescore=0 spamscore=0 bulkscore=0 priorityscore=1501 lowpriorityscore=0 suspectscore=0 clxscore=1015 phishscore=0 impostorscore=0 mlxlogscore=736 adultscore=0 mlxscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.19.0-2409260000 definitions=main-2410140094 Received-SPF: pass client-ip=148.163.156.1; envelope-from=stefanb@linux.ibm.com; helo=mx0a-001b2d01.pphosted.com X-Spam_score_int: -26 X-Spam_score: -2.7 X-Spam_bar: -- X-Spam_report: (-2.7 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, RCVD_IN_VALIDITY_CERTIFIED_BLOCKED=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=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: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On 10/11/24 6:35 PM, Stefan Berger wrote: > Error responses from swtpm are always only 4 bytes long. Therefore, read > the entire response in 2 passes and stop if the first 4 bytes indicate an > error response with no subsequent bytes readable. Read the rest in a 2nd > pass, if needed. This avoids getting stuck while waiting for too many bytes > if only 4 bytes were sent due to an error message. The 'getting stuck' > condition has not been observed in practice so far, though. > > Resolves: https://gitlab.com/qemu-project/qemu/-/issues/2615 > Signed-off-by: Stefan Berger > --- > backends/tpm/tpm_emulator.c | 25 +++++++++++++++++++++++-- > 1 file changed, 23 insertions(+), 2 deletions(-) > > diff --git a/backends/tpm/tpm_emulator.c b/backends/tpm/tpm_emulator.c > index b0e2fb3fc7..1b2e890668 100644 > --- a/backends/tpm/tpm_emulator.c > +++ b/backends/tpm/tpm_emulator.c > @@ -129,6 +129,9 @@ static int tpm_emulator_ctrlcmd(TPMEmulator *tpm, unsigned long cmd, void *msg, > uint32_t cmd_no = cpu_to_be32(cmd); > ssize_t n = sizeof(uint32_t) + msg_len_in; > uint8_t *buf = NULL; > + ptm_res res; > + off_t o = 0; > + int to_read; > > WITH_QEMU_LOCK_GUARD(&tpm->mutex) { > buf = g_alloca(n); > @@ -140,11 +143,29 @@ static int tpm_emulator_ctrlcmd(TPMEmulator *tpm, unsigned long cmd, void *msg, > return -1; > } > > - if (msg_len_out != 0) { > - n = qemu_chr_fe_read_all(dev, msg, msg_len_out); > + /* > + * Any response will be at least 4 bytes long. Error responses are only > + * 4 bytes (=sizeof(ptm_res)), though. Therefore, read response in 2 > + * passes, returning when an error response is encountered. > + */ v2: We need one exception here and that's CMD_GET_STATEBLOB since it has been sending a longer header since basically 'forever'. > + to_read = sizeof(res); > + while (msg_len_out > 0) { > + n = qemu_chr_fe_read_all(dev, (uint8_t *)msg + o, to_read); > if (n <= 0) { > return -1; > } > + msg_len_out -= to_read; > + if (msg_len_out == 0) { > + return 0; > + } > + > + memcpy(&res, msg, sizeof(res)); > + if (res) { > + return 0; > + } > + > + o = to_read; > + to_read = msg_len_out; > } > } >