From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id BAE9EC433FE for ; Tue, 12 Apr 2022 01:08:26 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1345847AbiDLBHh (ORCPT ); Mon, 11 Apr 2022 21:07:37 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:34710 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1346432AbiDLA64 (ORCPT ); Mon, 11 Apr 2022 20:58:56 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [145.40.68.75]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 17242340F7; Mon, 11 Apr 2022 17:51:56 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id AE8ABB819D5; Tue, 12 Apr 2022 00:51:55 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 32E03C385AA; Tue, 12 Apr 2022 00:51:53 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1649724714; bh=h7wCG4XjaYle+ieR3ESj44+7lHbRR0+fYce5PBuCF8I=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=oVa45DlrAIOIvYUfhnq2rpVcrzz3VudfY4QjjXSklUkcibRu73H3sx6ukSuBndNvy LYFZYkn2kzqSoADGOdkzi4UyJwxyZmAJavhUcZisDCUMmgCng3M7nbTA1OXgroDue4 CHp1y6YXqnpbSJPW8R/aYoLuYKZpojlbpCmRfn3EkBEEpjysIWQgnK48hXxn0oD09I teXZL+tWL7TY9s9qNdxM0RcAhFrpHT3tbIrUWaPvwLpORjx9+XxdyphKWhM5KZ7Qd5 80H9ppzwUvLCgAY7IZ3Q6GN3LNZ2+vGyBqk3URx1TgPD7XVndFTvm4MwrSYAppO0YM FmV1Bi0tnzxKA== From: Sasha Levin To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Michael Kelley , Andrea Parri , Wei Liu , Sasha Levin , kys@microsoft.com, haiyangz@microsoft.com, sthemmin@microsoft.com, decui@microsoft.com, linux-hyperv@vger.kernel.org Subject: [PATCH AUTOSEL 4.19 03/12] Drivers: hv: vmbus: Prevent load re-ordering when reading ring buffer Date: Mon, 11 Apr 2022 20:51:36 -0400 Message-Id: <20220412005148.351391-3-sashal@kernel.org> X-Mailer: git-send-email 2.35.1 In-Reply-To: <20220412005148.351391-1-sashal@kernel.org> References: <20220412005148.351391-1-sashal@kernel.org> MIME-Version: 1.0 X-stable: review X-Patchwork-Hint: Ignore Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Michael Kelley [ Upstream commit b6cae15b5710c8097aad26a2e5e752c323ee5348 ] When reading a packet from a host-to-guest ring buffer, there is no memory barrier between reading the write index (to see if there is a packet to read) and reading the contents of the packet. The Hyper-V host uses store-release when updating the write index to ensure that writes of the packet data are completed first. On the guest side, the processor can reorder and read the packet data before the write index, and sometimes get stale packet data. Getting such stale packet data has been observed in a reproducible case in a VM on ARM64. Fix this by using virt_load_acquire() to read the write index, ensuring that reads of the packet data cannot be reordered before it. Preventing such reordering is logically correct, and with this change, getting stale data can no longer be reproduced. Signed-off-by: Michael Kelley Reviewed-by: Andrea Parri (Microsoft) Link: https://lore.kernel.org/r/1648394710-33480-1-git-send-email-mikelley@microsoft.com Signed-off-by: Wei Liu Signed-off-by: Sasha Levin --- drivers/hv/ring_buffer.c | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-) diff --git a/drivers/hv/ring_buffer.c b/drivers/hv/ring_buffer.c index 6cb45f256107..d97b30af9e03 100644 --- a/drivers/hv/ring_buffer.c +++ b/drivers/hv/ring_buffer.c @@ -365,7 +365,16 @@ int hv_ringbuffer_read(struct vmbus_channel *channel, static u32 hv_pkt_iter_avail(const struct hv_ring_buffer_info *rbi) { u32 priv_read_loc = rbi->priv_read_index; - u32 write_loc = READ_ONCE(rbi->ring_buffer->write_index); + u32 write_loc; + + /* + * The Hyper-V host writes the packet data, then uses + * store_release() to update the write_index. Use load_acquire() + * here to prevent loads of the packet data from being re-ordered + * before the read of the write_index and potentially getting + * stale data. + */ + write_loc = virt_load_acquire(&rbi->ring_buffer->write_index); if (write_loc >= priv_read_loc) return write_loc - priv_read_loc; -- 2.35.1