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[88.21.202.17]) by smtp.gmail.com with ESMTPSA id a15sm16569792wrw.56.2020.05.11.00.10.49 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 11 May 2020 00:10:49 -0700 (PDT) Subject: Re: Abort in mch_update_pciexbar From: =?UTF-8?Q?Philippe_Mathieu-Daud=c3=a9?= To: Alexander Bulekov , qemu-devel@nongnu.org References: <20200511045912.keffhizkobgwqcag@mozz.bu.edu> Message-ID: <2344dc20-5c7f-75eb-96d2-bef0153550d6@redhat.com> Date: Mon, 11 May 2020 09:10:48 +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: 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=205.139.110.61; envelope-from=philmd@redhat.com; helo=us-smtp-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/05/11 03:10:56 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, 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: Stefan Hajnoczi , "Michael S. Tsirkin" Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" 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(); } --- But the real question is what would the real hardware do in this case. > >> 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.