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([2a00:23c5:5785:9a01:ad9a:ab78:5748:a7ec]) by smtp.gmail.com with ESMTPSA id p17sm16319687wrf.112.2022.01.25.05.55.19 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 25 Jan 2022 05:55:22 -0800 (PST) Message-ID: <2da0075f-4a6f-b196-6ae7-73c0df66e437@gmail.com> Date: Tue, 25 Jan 2022 13:55:19 +0000 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:91.0) Gecko/20100101 Thunderbird/91.5.0 Subject: Re: [PATCH v2] xen-mapcache: Avoid entry->lock overflow Content-Language: en-US To: Ross Lagerwall , Stefano Stabellini , Anthony Perard , Paul Durrant References: <20220124104450.152481-1-ross.lagerwall@citrix.com> From: "Durrant, Paul" In-Reply-To: <20220124104450.152481-1-ross.lagerwall@citrix.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Host-Lookup-Failed: Reverse DNS lookup failed for 2a00:1450:4864:20::332 (failed) Received-SPF: pass client-ip=2a00:1450:4864:20::332; envelope-from=xadimgnik@gmail.com; helo=mail-wm1-x332.google.com X-Spam_score_int: -12 X-Spam_score: -1.3 X-Spam_bar: - X-Spam_report: (-1.3 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, FREEMAIL_FROM=0.001, NICE_REPLY_A=-0.001, PDS_HP_HELO_NORDNS=0.001, RCVD_IN_DNSWL_NONE=-0.0001, RDNS_NONE=0.793, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=no 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: , Reply-To: paul@xen.org Cc: Eduardo Habkost , Igor Druzhinin , "Michael S. Tsirkin" , Richard Henderson , qemu-devel@nongnu.org, xen-devel@lists.xenproject.org, Paolo Bonzini Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 24/01/2022 10:44, Ross Lagerwall wrote: > In some cases, a particular mapcache entry may be mapped 256 times > causing the lock field to wrap to 0. For example, this may happen when > using emulated NVME and the guest submits a large scatter-gather write. > At this point, the entry map be remapped causing QEMU to write the wrong > data or crash (since remap is not atomic). > > Avoid this overflow by increasing the lock field to a uint32_t and also > detect it and abort rather than continuing regardless. > > Signed-off-by: Ross Lagerwall Reviewed-by: Paul Durrant > --- > Changes in v2: Change type to uint32_t since there is a hole there > anyway. The struct size remains at 48 bytes on x86_64. > > hw/i386/xen/xen-mapcache.c | 8 +++++++- > 1 file changed, 7 insertions(+), 1 deletion(-) > > diff --git a/hw/i386/xen/xen-mapcache.c b/hw/i386/xen/xen-mapcache.c > index bd47c3d672..f2ef977963 100644 > --- a/hw/i386/xen/xen-mapcache.c > +++ b/hw/i386/xen/xen-mapcache.c > @@ -52,7 +52,7 @@ typedef struct MapCacheEntry { > hwaddr paddr_index; > uint8_t *vaddr_base; > unsigned long *valid_mapping; > - uint8_t lock; > + uint32_t lock; > #define XEN_MAPCACHE_ENTRY_DUMMY (1 << 0) > uint8_t flags; > hwaddr size; > @@ -355,6 +355,12 @@ tryagain: > if (lock) { > MapCacheRev *reventry = g_malloc0(sizeof(MapCacheRev)); > entry->lock++; > + if (entry->lock == 0) { > + fprintf(stderr, > + "mapcache entry lock overflow: "TARGET_FMT_plx" -> %p\n", > + entry->paddr_index, entry->vaddr_base); > + abort(); > + } > reventry->dma = dma; > reventry->vaddr_req = mapcache->last_entry->vaddr_base + address_offset; > reventry->paddr_index = mapcache->last_entry->paddr_index;