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[88.21.202.17]) by smtp.gmail.com with ESMTPSA id k5sm15387981wrx.16.2020.05.11.00.42.57 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 11 May 2020 00:42:57 -0700 (PDT) Subject: Re: Abort in mch_update_pciexbar To: "Michael S. Tsirkin" References: <20200511045912.keffhizkobgwqcag@mozz.bu.edu> <2344dc20-5c7f-75eb-96d2-bef0153550d6@redhat.com> <20200511033045-mutt-send-email-mst@kernel.org> From: =?UTF-8?Q?Philippe_Mathieu-Daud=c3=a9?= Message-ID: <49e451a3-0cdf-39ba-db9c-c61af6a58492@redhat.com> Date: Mon, 11 May 2020 09:42:57 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.5.0 MIME-Version: 1.0 In-Reply-To: <20200511033045-mutt-send-email-mst@kernel.org> Content-Language: en-US X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=207.211.31.120; envelope-from=philmd@redhat.com; helo=us-smtp-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/05/11 02:55:57 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] 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, URIBL_BLOCKED=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: Alexander Bulekov , qemu-devel@nongnu.org, Stefan Hajnoczi Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 5/11/20 9:39 AM, Michael S. Tsirkin wrote: > On Mon, May 11, 2020 at 09:10:48AM +0200, Philippe Mathieu-Daudé wrote: >> On 5/11/20 8:19 AM, Philippe Mathieu-Daudé wrote: >>> On 5/11/20 6:59 AM, Alexander Bulekov wrote: >>>> Hello, >>>> While fuzzing, I found an input that triggers an assertion failure in >>>> mch_update_pciexbar: >>>> >>>> #6 0x7f38d387c55a in abort >>>> /build/glibc-GwnBeO/glibc-2.30/stdlib/abort.c:79:7 >>>> #7 0x55c27e94ffd0 in mch_update_pciexbar hw/pci-host/q35.c:331:9 >>>> #8 0x55c27e94db38 in mch_write_config hw/pci-host/q35.c:487:9 >>>> #9 0x55c27e9e3f4c in pci_host_config_write_common hw/pci/pci_host.c:81:5 >>>> #10 0x55c27e9e5307 in pci_data_write hw/pci/pci_host.c:118:5 >>>> #11 0x55c27e9e6601 in pci_host_data_write hw/pci/pci_host.c:165:9 >>>> #12 0x55c27ca3b17b in memory_region_write_accessor memory.c:496:5 >>>> #13 0x55c27ca3a5e4 in access_with_adjusted_size memory.c:557:18 >>>> #14 0x55c27ca38177 in memory_region_dispatch_write memory.c:1488:16 >>>> #15 0x55c27c721325 in flatview_write_continue exec.c:3174:23 >>>> #16 0x55c27c70994d in flatview_write exec.c:3214:14 >>>> #17 0x55c27c709462 in address_space_write exec.c:3305:18 >>> >>> These lines don't match QEMU v5.0.0. >>> >>>> >>>> I can reproduce it in a qemu 5.0 build using: >>>> cat << EOF | ~/Development/qemu/build/i386-softmmu/qemu-system-i386 >>>> -M pc-q35-5.0 -display none -nodefaults -nographic -qtest stdio >>>> outl 0xcf8 0xf2000060 >>>> outl 0xcfc 0x8400056e >>> >>> The guest shouldn't ask for a reserved bar length (grep for >>> MCH_HOST_BRIDGE_PCIEXBAR_LENGTH_RVD). I suppose we should simply report >>> it as GUEST_ERROR and ignore it. >> >> This patch prevent the crash: >> >> -- >8 -- >> diff --git a/hw/pci-host/q35.c b/hw/pci-host/q35.c >> index 2bbc90b28f..2b744aca93 100644 >> --- a/hw/pci-host/q35.c >> +++ b/hw/pci-host/q35.c >> @@ -36,6 +36,7 @@ >> #include "qapi/error.h" >> #include "qapi/visitor.h" >> #include "qemu/module.h" >> +#include "qemu/log.h" >> >> >> /**************************************************************************** >> * Q35 host >> @@ -320,6 +321,9 @@ static void mch_update_pciexbar(MCHPCIState *mch) >> addr_mask |= MCH_HOST_BRIDGE_PCIEXBAR_64ADMSK; >> break; >> case MCH_HOST_BRIDGE_PCIEXBAR_LENGTH_RVD: >> + qemu_log_mask(LOG_GUEST_ERROR, "%s: Invalid use of reserved >> value\n", >> + __func__); >> + return; >> default: >> abort(); >> } > > Maybe report the value too. This is a 2 bit field, all are covered except 0b11 which is the RESERVED case, and the abort() now will never fire. It is unclear why the compiler doesn't notice that. > >> --- >> >> But the real question is what would the real hardware do in this case. > > Spec doesn't say unfortunately. All it says is: > Designers must not rely on the absence or characteristics of any > features or instructions marked "reserved" or "undefined." Intel > reserves these for > > future definition and shall have no responsibility whatsoever > for conflicts or incompatibilities arising from future changes to them. OK, thanks for checking. I'll submit formal patch with proper description. > >>> >>>> EOF >>>> >>>> I also uploaded the above trace, in case the formatting is broken: >>>> >>>> curl https://paste.debian.net/plain/1146095 | qemu-system-i386 -M >>>> pc-q35-5.0 -display none -nodefaults -nographic -qtest stdio >>>> >>>> Please let me know if I can provide any further info. >>> >>> It would help the community if you fill your bug reports with Launchpad, >>> so they don't get lost in the high email flow, and we can track/update >>> them. See for example: >>> https://bugs.launchpad.net/qemu/+bug/1835865 and >>> https://lists.gnu.org/archive/html/qemu-devel/2020-03/msg06082.html >>> which refers it. >