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 B05ACC4332F for ; Tue, 12 Apr 2022 00:52:18 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S244990AbiDLAy0 (ORCPT ); Mon, 11 Apr 2022 20:54:26 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:42698 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S244383AbiDLAw0 (ORCPT ); Mon, 11 Apr 2022 20:52:26 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 6245231365; Mon, 11 Apr 2022 17:47:50 -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 dfw.source.kernel.org (Postfix) with ESMTPS id E89F2617DA; Tue, 12 Apr 2022 00:47:49 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 390ACC385A9; Tue, 12 Apr 2022 00:47:48 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1649724469; bh=Y+mN8yxB8UYnXBTzQwry6M5BRV4I9UhvtQahWGKhiB4=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=J4boLIkOZKqSRlYtDMSpXZcA4nNotP8Q2b0B0TKSIRywWiwURBcsKyfG8Mm+6S6wt teFWcozNB8gYJvkOz9c+i1jrWuMlj7uXp9eFLcScm24vD8EhWxjob3PvFkxGnuxqOT gaKdlg7geqbvvUuSJjhKpIQn61L6q/rN+IpxjMe/PM6A3t8rWBMGoAsNQD/rcHdwrd ZFeP0GxU15leO2USFvBu0L65s4XFZa4cMOh9v9TVpRUMbIQOVxjeVhVwIhhv0perEn vtqJybyX88C3JXriUJ3ef1Q3ZDunB7f4xU0nJwV3GwEut5y9Z15IcVU3TSYfOMklqA Vv8OKgaOMlXDQ== 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 5.15 14/41] Drivers: hv: vmbus: Prevent load re-ordering when reading ring buffer Date: Mon, 11 Apr 2022 20:46:26 -0400 Message-Id: <20220412004656.350101-14-sashal@kernel.org> X-Mailer: git-send-email 2.35.1 In-Reply-To: <20220412004656.350101-1-sashal@kernel.org> References: <20220412004656.350101-1-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 314015d9e912..f4091143213b 100644 --- a/drivers/hv/ring_buffer.c +++ b/drivers/hv/ring_buffer.c @@ -408,7 +408,16 @@ 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