From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 018DD3B1EE7; Tue, 13 Oct 2026 12:13:36 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791893617; cv=none; b=g+fzdnDkq7cqrdD8ujoIb37nodZ0HZCLfQifjJbYlhTwM56npEXoJX37J9/S1el1REc1nnaAMe1ElH4HpVcEvINgkTX3DA8IHZzcgiHuAO97ChCIcCXoP/4jxmKLDZadewVdD/D6IxQxuEixEeMTJ4hy5WnpBPr+Crxq6/jV+gg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791893617; c=relaxed/simple; bh=6TjBbdFVSbE291XbFGNQUllTa1ZQiuYzbWy4TsN+13s=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=oAFCYTv09MsVwu8KFdG8VgPTClxma9fPWb862axrn+fA8mvH1qCd5MFCwTiKs1nKWqDWcTN4xC0yi6DhO1cbxiwAHNihz+8OIBKZHSn0lla//hb/uv1VHhTuWv782sLKHKh0mLp5T/Kcp4pvDE24Jg1amVOv6kRC+orRU4GRxgk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=qbll9hhW; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="qbll9hhW" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 54CAB1F000FF; Tue, 13 Oct 2026 12:13:35 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1791893615; bh=OXeOKqYidRI/2gK9ufoS+gQUC2HshsIrYpjKfp4ADFc=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=qbll9hhWypG3PVMRuaVxnM7BCqhnQMMp+DqZsL+TukDNE2XU5RyMtz5gCH+2/0Tgf wfqghUYFj37RMKKv+k7y66e6bY+cnuJJxUVklzkYWoWvuycbj28h0Dso1JljW5OTdv nlWXD3KkZfOTmZ0cD7+5PrIEOkbzlk1cQ2kvGQMM= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Juergen Gross , Michael Bommarito , Sasha Levin Subject: [PATCH 6.18 284/621] xen/pvcalls: bound backend response req_id before indexing rsp[] Date: Tue, 13 Oct 2026 13:34:39 +0200 Message-ID: <20261013112927.599051596@linuxfoundation.org> X-Mailer: git-send-email 2.56.0 In-Reply-To: <20261013112920.855194808@linuxfoundation.org> References: <20261013112920.855194808@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.18-stable review patch. If anyone has any objections, please let me know. ------------------ From: Michael Bommarito [ Upstream commit d33846c8dcc06b83b7acdeac1e8bfbb5c0c26cb2 ] pvcalls_front_event_handler() takes req_id directly from the backend-supplied ring response and uses it to index the fixed-size bedata->rsp[] array for a memcpy() and a store, with no range check. A malicious or buggy backend can set req_id past PVCALLS_NR_RSP_PER_RING and drive an out-of-bounds write past the bedata allocation. req_id was also declared int while the wire field rsp->req_id is u32, so a range check on the signed value alone is insufficient: a backend req_id of 0xffffffff becomes -1, passes a >= PVCALLS_NR_RSP_PER_RING test and indexes bedata->rsp[-1]. Declare req_id as u32 so a single bound covers both ends. A backend that sends an out-of-range req_id has violated the wire protocol, so rather than silently dropping the response, log once and stop trusting the backend: set bedata->disabled. The event handler then ignores further responses, and the request paths that wait for a response return -EIO instead of blocking forever. This mirrors the fatal-error handling xen-netback uses (xenvif_fatal_tx_err()). The pvcalls frontend currently trusts its backend, so this is not a classic-Xen security issue, but it matters for hardening PV frontends against malicious backends (confidential and disaggregated deployments). Fixes: 2195046bfd69 ("xen/pvcalls: implement socket command and handle events") Suggested-by: Juergen Gross Assisted-by: Claude:claude-opus-4-8 Signed-off-by: Michael Bommarito Reviewed-by: Juergen Gross Signed-off-by: Juergen Gross Message-ID: <20260617014149.2647404-1-michael.bommarito@gmail.com> Signed-off-by: Sasha Levin --- drivers/xen/pvcalls-front.c | 88 ++++++++++++++++++++++++++++++++----- 1 file changed, 76 insertions(+), 12 deletions(-) diff --git a/drivers/xen/pvcalls-front.c b/drivers/xen/pvcalls-front.c index 4926d4badc578..59f5916826286 100644 --- a/drivers/xen/pvcalls-front.c +++ b/drivers/xen/pvcalls-front.c @@ -32,6 +32,7 @@ struct pvcalls_bedata { struct xen_pvcalls_front_ring ring; grant_ref_t ref; int irq; + bool disabled; struct list_head socket_mappings; spinlock_t socket_lock; @@ -131,6 +132,20 @@ static inline int get_request(struct pvcalls_bedata *bedata, int *req_id) return 0; } +/* + * Wait for the backend's response to req_id, or for the frontend to be + * disabled because the backend violated the wire protocol. Returns 0 once + * the response has arrived, or -EIO if the frontend was disabled. + */ +static int pvcalls_front_wait_rsp(struct pvcalls_bedata *bedata, u32 req_id) +{ + wait_event(bedata->inflight_req, + READ_ONCE(bedata->rsp[req_id].req_id) == req_id || + READ_ONCE(bedata->disabled)); + + return READ_ONCE(bedata->disabled) ? -EIO : 0; +} + static bool pvcalls_front_write_todo(struct sock_mapping *map) { struct pvcalls_data_intf *intf = map->active.ring; @@ -168,7 +183,8 @@ static irqreturn_t pvcalls_front_event_handler(int irq, void *dev_id) struct pvcalls_bedata *bedata; struct xen_pvcalls_response *rsp; uint8_t *src, *dst; - int req_id = 0, more = 0, done = 0; + u32 req_id = 0; + int more = 0, done = 0; if (dev == NULL) return IRQ_HANDLED; @@ -179,12 +195,31 @@ static irqreturn_t pvcalls_front_event_handler(int irq, void *dev_id) pvcalls_exit(); return IRQ_HANDLED; } + if (READ_ONCE(bedata->disabled)) { + pvcalls_exit(); + return IRQ_HANDLED; + } again: while (RING_HAS_UNCONSUMED_RESPONSES(&bedata->ring)) { rsp = RING_GET_RESPONSE(&bedata->ring, bedata->ring.rsp_cons); req_id = rsp->req_id; + if (req_id >= PVCALLS_NR_RSP_PER_RING) { + /* + * The backend supplied a req_id that would index + * bedata->rsp[] out of bounds: a protocol violation + * from a malicious or buggy backend. Log once, stop + * trusting this backend and disable the frontend rather + * than silently dropping the response and continuing. + */ + pr_err_once("pvcalls: backend sent out-of-range req_id %u, disabling frontend\n", + req_id); + WRITE_ONCE(bedata->disabled, true); + bedata->ring.rsp_cons++; + done = 1; + break; + } if (rsp->cmd == PVCALLS_POLL) { struct sock_mapping *map = (struct sock_mapping *)(uintptr_t) rsp->u.poll.id; @@ -217,7 +252,7 @@ static irqreturn_t pvcalls_front_event_handler(int irq, void *dev_id) } RING_FINAL_CHECK_FOR_RESPONSES(&bedata->ring, more); - if (more) + if (more && !READ_ONCE(bedata->disabled)) goto again; if (done) wake_up(&bedata->inflight_req); @@ -330,8 +365,11 @@ int pvcalls_front_socket(struct socket *sock) if (notify) notify_remote_via_irq(bedata->irq); - wait_event(bedata->inflight_req, - READ_ONCE(bedata->rsp[req_id].req_id) == req_id); + ret = pvcalls_front_wait_rsp(bedata, req_id); + if (ret) { + pvcalls_exit(); + return ret; + } /* read req_id, then the content */ smp_rmb(); @@ -477,8 +515,11 @@ int pvcalls_front_connect(struct socket *sock, struct sockaddr *addr, if (notify) notify_remote_via_irq(bedata->irq); - wait_event(bedata->inflight_req, - READ_ONCE(bedata->rsp[req_id].req_id) == req_id); + ret = pvcalls_front_wait_rsp(bedata, req_id); + if (ret) { + pvcalls_exit_sock(sock); + return ret; + } /* read req_id, then the content */ smp_rmb(); @@ -711,8 +752,11 @@ int pvcalls_front_bind(struct socket *sock, struct sockaddr *addr, int addr_len) if (notify) notify_remote_via_irq(bedata->irq); - wait_event(bedata->inflight_req, - READ_ONCE(bedata->rsp[req_id].req_id) == req_id); + ret = pvcalls_front_wait_rsp(bedata, req_id); + if (ret) { + pvcalls_exit_sock(sock); + return ret; + } /* read req_id, then the content */ smp_rmb(); @@ -761,8 +805,11 @@ int pvcalls_front_listen(struct socket *sock, int backlog) if (notify) notify_remote_via_irq(bedata->irq); - wait_event(bedata->inflight_req, - READ_ONCE(bedata->rsp[req_id].req_id) == req_id); + ret = pvcalls_front_wait_rsp(bedata, req_id); + if (ret) { + pvcalls_exit_sock(sock); + return ret; + } /* read req_id, then the content */ smp_rmb(); @@ -820,6 +867,14 @@ int pvcalls_front_accept(struct socket *sock, struct socket *newsock, } } + if (READ_ONCE(bedata->disabled)) { + clear_bit(PVCALLS_FLAG_ACCEPT_INFLIGHT, + (void *)&map->passive.flags); + wake_up(&map->passive.inflight_accept_req); + pvcalls_exit_sock(sock); + return -EIO; + } + map2 = kzalloc(sizeof(*map2), GFP_KERNEL); if (map2 == NULL) { clear_bit(PVCALLS_FLAG_ACCEPT_INFLIGHT, @@ -880,10 +935,18 @@ int pvcalls_front_accept(struct socket *sock, struct socket *newsock, } if (wait_event_interruptible(bedata->inflight_req, - READ_ONCE(bedata->rsp[req_id].req_id) == req_id)) { + READ_ONCE(bedata->rsp[req_id].req_id) == req_id || + READ_ONCE(bedata->disabled))) { pvcalls_exit_sock(sock); return -EINTR; } + if (READ_ONCE(bedata->disabled)) { + clear_bit(PVCALLS_FLAG_ACCEPT_INFLIGHT, + (void *)&map->passive.flags); + wake_up(&map->passive.inflight_accept_req); + pvcalls_exit_sock(sock); + return -EIO; + } /* read req_id, then the content */ smp_rmb(); @@ -1054,7 +1117,8 @@ int pvcalls_front_release(struct socket *sock) notify_remote_via_irq(bedata->irq); wait_event(bedata->inflight_req, - READ_ONCE(bedata->rsp[req_id].req_id) == req_id); + READ_ONCE(bedata->rsp[req_id].req_id) == req_id || + READ_ONCE(bedata->disabled)); if (map->active_socket) { /* -- 2.53.0