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a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1789471343; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding; bh=NToK3ir8VnPlFCa5l6tn2sGAPeTADGZWya5exlgZPBw=; b=HETs8fd2FJIiIFodkkpvWt8dqal5W+BuPb7XdcKaOsgaAj+gQG6b4K7YDr79FwjRHQPU79 S3Vl3tBsQtsCD3zHyc2Y8TASTmPooLq6q43GV6hfn71EVxFl3M+imjDt+D5JUw6cxm9TEn AIalV658jAFxPipdlF8gw0KnTPhBfXs= X-MC-Unique: Wgddktg_NWqFRWsfC-09kQ-1 X-Mimecast-MFC-AGG-ID: Wgddktg_NWqFRWsfC-09kQ_1789471338 From: Thomas Huth To: qemu-devel@nongnu.org Cc: Peter Maydell , kraxel@redhat.com, Alexander Bulekov , qemu-stable@nongnu.org, Guannan Wang , Zhanpeng Liu , Jiashuo Liang <761232680@qq.com>, Guancheng Li Subject: [PATCH] hw/usb/hcd-xhci: Set reentrancy guard in timer functions (CVE-2026-17588) Date: Tue, 15 Sep 2026 13:22:13 +0200 Message-ID: <20260915112213.525283-1-thuth@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.93 Received-SPF: pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; helo=lists1p.gnu.org; Received-SPF: pass client-ip=170.10.129.124; envelope-from=thuth@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: 12 X-Spam_score: 1.2 X-Spam_bar: + X-Spam_report: (1.2 / 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, RCVD_IN_SBL_CSS=3.335, SPF_HELO_PASS=-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: qemu development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: qemu-devel-bounces+importer=patchew.org@nongnu.org X-ZohoMail-DKIM: pass (identity @redhat.com) X-ZM-MESSAGEID: 1789471408112158500 Content-Type: text/plain; charset="utf-8" The xHCI controller processes USB events from timer callbacks (xhci_mfwrap_timer and xhci_ep_kick_timer) outside of any MMIO handler context. The device's mem_reentrancy_guard is therefore not engaged during this processing. A malicious guest can exploit this by pointing the event ring base address (er_start) at the xHCI doorbell MMIO region. When xhci_write_event() performs a DMA write to deliver a transfer completion event, the write lands on doorbell register 0. If the written value is 0, this triggers xhci_process_commands() reentrantly. A CR_DISABLE_SLOT command prepared on the command ring then frees endpoint and transfer objects via xhci_disable_ep() / g_free() while the outer call stack still holds references to them, causing a heap use-after-free. Fix this by setting engaged_in_io on the device's mem_reentrancy_guard around the processing in these non-MMIO entry points. This mirrors the protection that EHCI, DWC2, and UHCI already have via qemu_bh_new_guarded(). With the guard active, the memory subsystem's automatic reentrancy check (system/memory.c) blocks DMA writes that would dispatch into the device's own MMIO handlers. CVE: CVE-2026-17588 Resolves: https://gitlab.com/qemu-project/qemu/-/work_items/3926 Reported-by: XlabAI Team of Tencent Xuanwu Lab , Guannan Wang , Zhanpeng Liu , Jiashuo Liang <761232680@qq.com>, Guancheng Li Resolves: https://gitlab.com/qemu-project/qemu/-/work_items/4195 Reported By: Ken Hsu and Royce Lu of Palo Alto Networks Signed-off-by: Thomas Huth Reviewed-by: Philippe Mathieu-Daud=C3=A9 --- hw/usb/hcd-xhci.c | 13 +++++++++++++ 1 file changed, 13 insertions(+) diff --git a/hw/usb/hcd-xhci.c b/hw/usb/hcd-xhci.c index d342aa2739e..12f8ffece0f 100644 --- a/hw/usb/hcd-xhci.c +++ b/hw/usb/hcd-xhci.c @@ -456,9 +456,15 @@ static void xhci_mfwrap_timer(void *opaque) { XHCIState *xhci =3D opaque; XHCIEvent wrap =3D { ER_MFINDEX_WRAP, CC_SUCCESS }; + MemReentrancyGuard *guard =3D &xhci->parent.mem_reentrancy_guard; + + assert(!guard->engaged_in_io); + guard->engaged_in_io =3D true; =20 xhci_event(xhci, &wrap, 0); xhci_mfwrap_update(xhci); + + guard->engaged_in_io =3D false; } =20 static void xhci_die(XHCIState *xhci) @@ -1086,7 +1092,14 @@ static void xhci_set_ep_state(XHCIState *xhci, XHCIE= PContext *epctx, static void xhci_ep_kick_timer(void *opaque) { XHCIEPContext *epctx =3D opaque; + MemReentrancyGuard *guard =3D &epctx->xhci->parent.mem_reentrancy_guar= d; + + assert(!guard->engaged_in_io); + guard->engaged_in_io =3D true; + xhci_kick_epctx(epctx, 0); + + guard->engaged_in_io =3D false; } =20 static XHCIEPContext *xhci_alloc_epctx(XHCIState *xhci, --=20 2.55.0