From: Lalithambika Krishnakumar <lalithambika.krishnakumar@xxxxxxxxx> [ Upstream commit 62df80165d7f197c9c0652e7416164f294a96661 ] While handling the completion queue, keep a local copy of the command id from the DMA-accessible completion entry. This silences a time-of-check to time-of-use (TOCTOU) warning from KF/x[1], with respect to a Thunderclap[2] vulnerability analysis. The double-read impact appears benign. There may be a theoretical window for @command_id to be used as an adversary-controlled array-index-value for mounting a speculative execution attack, but that mitigation is saved for a potential follow-on. A man-in-the-middle attack on the data payload is out of scope for this analysis and is hopefully mitigated by filesystem integrity mechanisms. [1] https://github.com/intel/kernel-fuzzer-for-xen-project [2] http://thunderclap.io/thunderclap-paper-ndss2019.pdf Signed-off-by: Lalithambika Krishna Kumar <lalithambika.krishnakumar@xxxxxxxxx> Signed-off-by: Christoph Hellwig <hch@xxxxxx> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> --- drivers/nvme/host/pci.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) diff --git a/drivers/nvme/host/pci.c b/drivers/nvme/host/pci.c index 143f16a9f8d7e..a89d74c5cd1a7 100644 --- a/drivers/nvme/host/pci.c +++ b/drivers/nvme/host/pci.c @@ -967,6 +967,7 @@ static inline struct blk_mq_tags *nvme_queue_tagset(struct nvme_queue *nvmeq) static inline void nvme_handle_cqe(struct nvme_queue *nvmeq, u16 idx) { struct nvme_completion *cqe = &nvmeq->cqes[idx]; + __u16 command_id = READ_ONCE(cqe->command_id); struct request *req; /* @@ -975,17 +976,17 @@ static inline void nvme_handle_cqe(struct nvme_queue *nvmeq, u16 idx) * aborts. We don't even bother to allocate a struct request * for them but rather special case them here. */ - if (unlikely(nvme_is_aen_req(nvmeq->qid, cqe->command_id))) { + if (unlikely(nvme_is_aen_req(nvmeq->qid, command_id))) { nvme_complete_async_event(&nvmeq->dev->ctrl, cqe->status, &cqe->result); return; } - req = blk_mq_tag_to_rq(nvme_queue_tagset(nvmeq), cqe->command_id); + req = blk_mq_tag_to_rq(nvme_queue_tagset(nvmeq), command_id); if (unlikely(!req)) { dev_warn(nvmeq->dev->ctrl.device, "invalid id %d completed on queue %d\n", - cqe->command_id, le16_to_cpu(cqe->sq_id)); + command_id, le16_to_cpu(cqe->sq_id)); return; } -- 2.27.0
