From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from linux.microsoft.com (linux.microsoft.com [13.77.154.182]) by smtp.subspace.kernel.org (Postfix) with ESMTP id A54E7437448; Thu, 1 Oct 2026 22:11:35 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=13.77.154.182 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790892697; cv=none; b=WYMC5h5FzXZBdinSQlAyYbv0wRRlmysvJe28S28BBgtYyx0jULZkFeR+QMfFqhDwMJHwhYl/xzxcTMJmCLQ5ZpS2mTb5GnG5BB39jO9GQb2xRPesTNCUYBjyKJnvmq/fVbbMEEDJcx12gIgXYwgP4bTfsFlrkN7lSpWLFHxccIQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790892697; c=relaxed/simple; bh=i5dGuL+vmCk0H0P/olMRt7aH85cUGBzKK2mmuD1WHqE=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=tlJybo5ZkaGjMc5r4MG2+EieDGrotEeds7yg4tgFlotZChOx3h1Mh0Mz1mQk7jVQRqZmDLoVsazPjqzULVniODXbow8YWbYAFNlJpLqky9OlbpsS8N4LkJV50JKZ2EhOP9/4VDAZjB5c1xVrik4N5RPbfrZlXBcX/WNPzU+8AvY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.microsoft.com; spf=pass smtp.mailfrom=linux.microsoft.com; dkim=pass (1024-bit key) header.d=linux.microsoft.com header.i=@linux.microsoft.com header.b=ZssPztoY; arc=none smtp.client-ip=13.77.154.182 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.microsoft.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.microsoft.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.microsoft.com header.i=@linux.microsoft.com header.b="ZssPztoY" Received: from linuxonhyperv3.guj3yctzbm1etfxqx2vob5hsef.xx.internal.cloudapp.net (linux.microsoft.com [13.77.154.182]) by linux.microsoft.com (Postfix) with ESMTPSA id 524ED20B7171; Thu, 1 Oct 2026 15:10:42 -0700 (PDT) DKIM-Filter: OpenDKIM Filter v2.11.0 linux.microsoft.com 524ED20B7171 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.microsoft.com; s=default; t=1790892642; bh=qFQdVdooSZcP5uYUJo8WJDgVWEs1roO5BJFHiMbw/4c=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=ZssPztoYw0prPqhe48Icws8j333qOTcJ2OEAAs/rmRitoD1HwqvWaSwkYCVAqLC0E ZpToPhogXl0XzSTjkLr9NV1KJiFBwscnqs0yspwOiMmBg4VpKXbs5dkjaLTNPUrHhW YBVAG85Y1hXa75nq/yOnsKk11uMsfGrg0RWjqKR0= From: Kameron Carr To: Haiyang Zhang , Wei Liu , Dexuan Cui , Long Li , Michael Kelley Cc: linux-hyperv@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH 4/4] Drivers: hv: vmbus: Keep the ring byte counts sane for a bad index Date: Thu, 1 Oct 2026 15:10:40 -0700 Message-ID: <20261001221040.1794904-5-kameroncarr@linux.microsoft.com> X-Mailer: git-send-email 2.43.7 In-Reply-To: <20261001221040.1794904-1-kameroncarr@linux.microsoft.com> References: <20261001221040.1794904-1-kameroncarr@linux.microsoft.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit The remaining users of the shared indices can't cause a bad memory access with the channels a CoCo VM accepts today, but an out-of-range index gives them a nonsense byte count. Give them defined behavior instead. hv_pkt_iter_first() bounds its memcpy() by hv_pkt_iter_avail(), which is derived from write_index, and by pkt_buffer_size, which comes from max_pkt_size and can exceed ring_datasize. A bad write index can then make it read past the end of the ring. Only KVP has such a max_pkt_size (16K on a 12K ring with 4K pages), and vmbus_is_valid_offer() rejects it in isolated VMs, so this is latent. hv_pkt_iter_avail() now reports an empty ring for a bad write index and logs it, rate-limited like hv_ringbuffer_write(). It takes the channel instead of the ring so the message can include the relid. hv_get_bytes_to_read() and hv_get_bytes_to_write() now return 0 for a bad index, so callers see nothing to read and no room to write. This also stops hv_end_read() from reporting data that hv_pkt_iter_first() won't return, which would keep a channel rescheduling its callback. hv_pkt_iter_close() only uses the indices to decide whether to signal the host, so skip the signal if either is out of range. Signed-off-by: Kameron Carr --- drivers/hv/ring_buffer.c | 15 +++++++++++++-- include/linux/hyperv.h | 6 ++++++ 2 files changed, 19 insertions(+), 2 deletions(-) diff --git a/drivers/hv/ring_buffer.c b/drivers/hv/ring_buffer.c index 29edab9..b54a7d3 100644 --- a/drivers/hv/ring_buffer.c +++ b/drivers/hv/ring_buffer.c @@ -408,8 +408,9 @@ int hv_ringbuffer_read(struct vmbus_channel *channel, * This is similar to hv_get_bytes_to_read but with private * read index instead. */ -static u32 hv_pkt_iter_avail(const struct hv_ring_buffer_info *rbi) +static u32 hv_pkt_iter_avail(const struct vmbus_channel *channel) { + const struct hv_ring_buffer_info *rbi = &channel->inbound; u32 priv_read_loc = rbi->priv_read_index; u32 write_loc; @@ -421,6 +422,12 @@ static u32 hv_pkt_iter_avail(const struct hv_ring_buffer_info *rbi) * stale data. */ write_loc = virt_load_acquire(&rbi->ring_buffer->write_index); + if (unlikely(!hv_ringbuffer_index_valid(rbi, write_loc))) { + pr_err_ratelimited("inbound write index out of range: relid %u write %u size %u\n", + channel->offermsg.child_relid, write_loc, + rbi->ring_datasize); + return 0; + } if (write_loc >= priv_read_loc) return write_loc - priv_read_loc; @@ -441,7 +448,7 @@ struct vmpacket_descriptor *hv_pkt_iter_first(struct vmbus_channel *channel) hv_debug_delay_test(channel, MESSAGE_DELAY); - bytes_avail = hv_pkt_iter_avail(rbi); + bytes_avail = hv_pkt_iter_avail(channel); if (bytes_avail < sizeof(struct vmpacket_descriptor)) return NULL; bytes_avail = min(rbi->pkt_buffer_size, bytes_avail); @@ -590,6 +597,10 @@ void hv_pkt_iter_close(struct vmbus_channel *channel) */ virt_rmb(); write_index = READ_ONCE(rbi->ring_buffer->write_index); + if (unlikely(!hv_ringbuffer_index_valid(rbi, write_index) || + !hv_ringbuffer_index_valid(rbi, start_read_index))) + return; + curr_write_sz = hv_ringbuffer_avail_write(rbi, rbi->priv_read_index, write_index); bytes_read = hv_pkt_iter_bytes_read(rbi, start_read_index); diff --git a/include/linux/hyperv.h b/include/linux/hyperv.h index 9d7d09c..fd61382 100644 --- a/include/linux/hyperv.h +++ b/include/linux/hyperv.h @@ -248,6 +248,9 @@ static inline u32 hv_get_bytes_to_read(const struct hv_ring_buffer_info *rbi) read_loc = READ_ONCE(rbi->ring_buffer->read_index); write_loc = READ_ONCE(rbi->ring_buffer->write_index); + if (unlikely(!hv_ringbuffer_index_valid(rbi, read_loc) || + !hv_ringbuffer_index_valid(rbi, write_loc))) + return 0; return hv_ringbuffer_avail_read(rbi, read_loc, write_loc); } @@ -258,6 +261,9 @@ static inline u32 hv_get_bytes_to_write(const struct hv_ring_buffer_info *rbi) read_loc = READ_ONCE(rbi->ring_buffer->read_index); write_loc = READ_ONCE(rbi->ring_buffer->write_index); + if (unlikely(!hv_ringbuffer_index_valid(rbi, read_loc) || + !hv_ringbuffer_index_valid(rbi, write_loc))) + return 0; return hv_ringbuffer_avail_write(rbi, read_loc, write_loc); } -- 2.45.4