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Tue, 19 May 2020 13:19:39 +0000 (UTC) Date: Tue, 19 May 2020 15:19:36 +0200 From: Cornelia Huck To: Collin Walling Subject: Re: [PATCH v2 3/8] s390/sclp: rework sclp boundary and length checks Message-ID: <20200519151936.1071fa14.cohuck@redhat.com> In-Reply-To: References: <20200515222032.18838-1-walling@linux.ibm.com> <20200515222032.18838-4-walling@linux.ibm.com> <2fcd0d94-12c7-e3b8-d6a6-3c512ae25150@linux.ibm.com> Organization: Red Hat GmbH MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=205.139.110.61; envelope-from=cohuck@redhat.com; helo=us-smtp-delivery-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/05/18 23:19:13 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-0.001, SPF_PASS=-0.001 autolearn=_AUTOLEARN 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: thuth@redhat.com, Janosch Frank , david@redhat.com, mst@redhat.com, qemu-devel@nongnu.org, pasic@linux.ibm.com, borntraeger@de.ibm.com, qemu-s390x@nongnu.org, svens@linux.ibm.com, pbonzini@redhat.com, mihajlov@linux.ibm.com, rth@twiddle.net Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Mon, 18 May 2020 11:15:07 -0400 Collin Walling wrote: > On 5/18/20 4:50 AM, Janosch Frank wrote: > > On 5/16/20 12:20 AM, Collin Walling wrote: > >> Rework the SCLP boundary check to account for different SCLP commands > >> (eventually) allowing different boundary sizes. > >> > >> Move the length check code into a separate function, and introduce a > >> new function to determine the length of the read SCP data (i.e. the size > >> from the start of the struct to where the CPU entries should begin). > >> > >> Signed-off-by: Collin Walling > >> --- > >> hw/s390x/sclp.c | 57 ++++++++++++++++++++++++++++++++++++++++++------- > >> 1 file changed, 49 insertions(+), 8 deletions(-) > >> > >> diff --git a/hw/s390x/sclp.c b/hw/s390x/sclp.c > >> index 2bd618515e..987699e3c4 100644 > >> --- a/hw/s390x/sclp.c > >> +++ b/hw/s390x/sclp.c > >> @@ -49,6 +49,34 @@ static inline bool sclp_command_code_valid(uint32_t code) > >> return false; > >> } > >> > >> +static bool sccb_has_valid_boundary(uint64_t sccb_addr, uint32_t code, > >> + SCCBHeader *header) > >> +{ > >> + uint64_t current_len = sccb_addr + be16_to_cpu(header->length); > >> + uint64_t allowed_len = (sccb_addr & PAGE_MASK) + PAGE_SIZE; > > > > Those are addresses not length indications and the names should reflect > > that. > > True > > > Also don't we need to use PAGE_SIZE - 1? > > > > Technically we need to -1 on both sides since length denotes the size of > the sccb in bytes, not the max address. > > How about this: > > s/current_len/sccb_max_addr > s/allowed_len/sccb_boundary +1, like the names. > > -1 to sccb_max_addr > > Change the check to: sccb_max_addr < sccb_boundary > > ? > > > I'm still trying to wake up, so take this with a grain of salt. > > > > No worries. I appreciate the review nonetheless :) > > >> + > >> + switch (code & SCLP_CMD_CODE_MASK) { > >> + default: > >> + if (current_len <= allowed_len) { > >> + return true; > >> + } > >> + } > >> + header->response_code = cpu_to_be16(SCLP_RC_SCCB_BOUNDARY_VIOLATION); > >> + return false; > >> +} > >> + > >> +/* Calculates sufficient SCCB length to store a full Read SCP/CPU response */ > >> +static bool sccb_has_sufficient_len(SCCB *sccb, int num_cpus, int data_len) > >> +{ > >> + int required_len = data_len + num_cpus * sizeof(CPUEntry); > >> + > >> + if (be16_to_cpu(sccb->h.length) < required_len) { > >> + sccb->h.response_code = cpu_to_be16(SCLP_RC_INSUFFICIENT_SCCB_LENGTH); > >> + return false; > >> + } > >> + return true; > >> +} > > > > Hm, from the function name alone I'd not have expected it to also set > > the response code. > > > > It also sets the required length in the header for an extended-length > sccb. Perhaps this function name doesn't hold up well. > > Does sccb_check_sufficient_len make more sense? To me it does. > > I think the same could be said of the boundary check function, which > also sets the response code. > > What about setting the response code outside the function, similar to > what sclp_comand_code_valid does? Whatever results in the least code churn to make it consistent ;) > > >> + > >> static void prepare_cpu_entries(MachineState *ms, CPUEntry *entry, int *count) > >> { > >> uint8_t features[SCCB_CPU_FEATURE_LEN] = { 0 }; > >> @@ -66,6 +94,16 @@ static void prepare_cpu_entries(MachineState *ms, CPUEntry *entry, int *count) > >> } > >> } > >> > >> +/* > >> + * The data length denotes the start of the struct to where the first > >> + * CPU entry is to be allocated. This value also denotes the offset_cpu > >> + * field. > >> + */ > >> +static int get_read_scp_info_data_len(void) > >> +{ > >> + return offsetof(ReadInfo, entries); > >> +} > > > > Not sure what the policy for this is, but maybe this can go into a > > header file? > > David and Conny will surely make that clear to me :) > > > > Not sure either. If anything it might be a good candidate for an inline > function. If we don't process read info outside of this file, no need to move it to a header. The compiler is probably also smart enough to inline it on its own, I guess.