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Violators will be prosecuted; (version=TLSv1/SSLv3 cipher=AES256-GCM-SHA384 bits=256/256) Tue, 18 Jun 2019 19:53:44 +0100 Received: from d06av24.portsmouth.uk.ibm.com (d06av24.portsmouth.uk.ibm.com [9.149.105.60]) by b06avi18626390.portsmouth.uk.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id x5IIrZ1s37093632 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Tue, 18 Jun 2019 18:53:35 GMT Received: from d06av24.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 2E6B542059; Tue, 18 Jun 2019 18:53:43 +0000 (GMT) Received: from d06av24.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 274E442057; Tue, 18 Jun 2019 18:53:42 +0000 (GMT) Received: from dhcp-9-31-103-88.watson.ibm.com (unknown [9.31.103.88]) by d06av24.portsmouth.uk.ibm.com (Postfix) with ESMTP; Tue, 18 Jun 2019 18:53:42 +0000 (GMT) Subject: Re: [PATCH] ima: dynamically allocate shash_desc From: Mimi Zohar To: Arnd Bergmann Cc: Dmitry Kasatkin , James Morris , "Serge E. Hallyn" , Jarkko Sakkinen , Stefan Berger , linux-integrity@vger.kernel.org, LSM List , Linux Kernel Mailing List Date: Tue, 18 Jun 2019 14:53:41 -0400 In-Reply-To: References: <20190617115838.2397872-1-arnd@arndb.de> <1560786951.4072.103.camel@linux.ibm.com> <1560794826.4072.169.camel@linux.ibm.com> <1560861878.9530.17.camel@linux.ibm.com> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.20.5 (3.20.5-1.fc24) Mime-Version: 1.0 Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 x-cbid: 19061818-0028-0000-0000-0000037B67D4 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 19061818-0029-0000-0000-0000243B72C5 Message-Id: <1560884021.9530.39.camel@linux.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2019-06-18_08:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=3 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1810050000 definitions=main-1906180148 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 2019-06-18 at 20:06 +0200, Arnd Bergmann wrote: > On Tue, Jun 18, 2019 at 3:55 PM Mimi Zohar wrote: > > > > On Mon, 2019-06-17 at 22:08 +0200, Arnd Bergmann wrote: > > > On Mon, Jun 17, 2019 at 8:08 PM Mimi Zohar wrote: > > > > > > > > On Mon, 2019-06-17 at 11:55 -0400, Mimi Zohar wrote: > > > > > On Mon, 2019-06-17 at 13:20 +0200, Arnd Bergmann wrote: > > > > > > On 32-bit ARM, we get a warning about excessive stack usage when > > > > > > building with clang. > > > > > > > > > > > > security/integrity/ima/ima_crypto.c:504:5: error: stack frame size > > > > > > of 1152 bytes in function 'ima_calc_field_array_hash' [-Werror,- > > > > > > Wframe-larger-than=] > > > > > > > > > > I'm definitely not seeing this. Is this problem a result of non > > > > > upstreamed patches? For sha1, currently the only possible hash > > > > > algorithm, I'm seeing 664. > > > > > > You won't see it with gcc, only with clang in some randconfig builds, > > > I suppose only when KASAN is enabled. > > > > > > > Every time a measurement is added to the measurement list, the memory > > > > would be allocated/freed. The frequency of new measurements is policy > > > > dependent. For performance reasons, I'd prefer if the allocation > > > > remains on the stack. > > > > > > Is there a way to preallocate the shash_desc instead? That would > > > avoid the overhead. > > > > There are 3 other SHASH_DESC_ON_STACK definitions in just > > ima_crypto.c, with a total of ~55 other places in the kernel. Before > > fixing this particular function, I'd like to know if the "excessive > > stack usage" warning is limited to ima_calc_field_array_hash_tfm(). > > If so, what is so special about its usage of SHASH_DESC_ON_STACK? > > SHASH_DESC_ON_STACK() uses at least 512 bytes of stack > everywhere, which is half of the warning limit for a function on > 32 bit kernels. > > With KASAN, a small redzone is put around it so we can detect out > of bounds access to a variable that is passed by reference. > clang makes that buffer larger than gcc, so we end up with something > like 768 bytes for each instance of SHASH_DESC_ON_STACK(). > > Most other users still stay below the 1024 byte warning level though, > because typical functions only use a few bytes of stack space. > In case of ima_calc_field_array_hash_tfm(), the is also the buffer[] > array of 255 bytes that gets another large redzone. > > I fixed up all the (randconfig) warnings I get for arm32, arm64 and > x86 kernels, and I think there were four to five that were because of > SHASH_DESC_ON_STACK(). It might make sense to convert all > three instances in ima to preallocate the descriptor if we do it for > one of them, even when it's not actually needed. "buffer" is only used for the original "ima" template format, which is limited to sha1.  Rather than allocating shash, I would prefer "buffer" be allocated, if needed, and only the first time. Mimi