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 691C6C433EF for ; Tue, 12 Apr 2022 01:03:01 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1344968AbiDLBFF (ORCPT ); Mon, 11 Apr 2022 21:05:05 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:47392 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1345183AbiDLA63 (ORCPT ); Mon, 11 Apr 2022 20:58:29 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 9093533A2A; Mon, 11 Apr 2022 17:51:08 -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 2BD9960B2E; Tue, 12 Apr 2022 00:51:08 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 6BAD7C385A4; Tue, 12 Apr 2022 00:51:06 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1649724667; bh=9T8bL2EPWJPPlfceRC/6fA7bh51kA+mxwyKL6iDHjn8=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=kYHaS+HqovoSv7KKvhFuShNiWrEz3PpC/J994aO/UZerE72NoTxLnue520tDJ2NfC 1SAW9oajAGifoKegNo6U3XRRTnv7u+oInVTo/jvjnpmtF3IrJyhMisFq23PzhHAg0p iiJBu+jzkeU0QcKB23vcjiOKIjg0pP1EFg/vIFWsO80loGul3GAato5N0i0FES9azK fFbjltiipacPKYRZqwDYVocea+t9Ibs4XFdrmNy8YWs3YwZ0VeFo7OkapZ/XxfW1em G37iFJVs6BimKktS8Ly3dQgEFd0qbjD6e0IyPYWnWHJ/BdSpTmAVu0qEXlFfdn+Hez V2bJP5kpJmXAQ== 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 5.4 06/21] Drivers: hv: vmbus: Prevent load re-ordering when reading ring buffer Date: Mon, 11 Apr 2022 20:50:25 -0400 Message-Id: <20220412005042.351105-6-sashal@kernel.org> X-Mailer: git-send-email 2.35.1 In-Reply-To: <20220412005042.351105-1-sashal@kernel.org> References: <20220412005042.351105-1-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 9a03b163cbbd..59f1e64908b1 100644 --- a/drivers/hv/ring_buffer.c +++ b/drivers/hv/ring_buffer.c @@ -378,7 +378,16 @@ 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