[PATCH 6.6.y] nvme-fabrics: use reserved tag for reg read/write command

[Artem Dinaburg <artem@trailofbits.com>]

From: Chunguang Xu <chunguang.xu@shopee.com>

[ Upstream commit 7dc3bfcb4c9cc58970fff6aaa48172cb224d85aa ]

In some scenarios, if too many commands are issued by nvme command in
the same time by user tasks, this may exhaust all tags of admin_q. If
a reset (nvme reset or IO timeout) occurs before these commands finish,
reconnect routine may fail to update nvme regs due to insufficient tags,
which will cause kernel hang forever. In order to workaround this issue,
maybe we can let reg_read32()/reg_read64()/reg_write32() use reserved
tags. This maybe safe for nvmf:

1. For the disable ctrl path,  we will not issue connect command
2. For the enable ctrl / fw activate path, since connect and reg_xx()
   are called serially.

So the reserved tags may still be enough while reg_xx() use reserved tags.

[ Backport to 6.6.y: used the older BLK_MQ_REQ_RESERVED request flag. ]

Signed-off-by: Chunguang Xu <chunguang.xu@shopee.com>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Keith Busch <kbusch@kernel.org>
Assisted-by: LLM
Signed-off-by: Artem Dinaburg <artem@trailofbits.com>
---
Hi Greg, Sasha, and nvme maintainers,

I am working through the small CVE backports still missing from 6.6.y.
This one addresses CVE-2024-41082. It reserves a request tag for
controller-register I/O during reconnect and reset.

The fix is already present in 6.12.y, 6.18.y, and 7.2.y, but not in 6.6.y.
This fix also affects 6.1.y, which will need a separate backport; this
submission contains only the 6.6.y patch.
The target-specific adjustment is recorded in the bracketed note above.

Could you please queue it for 6.6.y?

CVE: CVE-2024-41082
Upstream: 7dc3bfcb4c9cc58970fff6aaa48172cb224d85aa

AI assistance: An LLM helped identify, adapt, and validate this backport; I
reviewed the resulting code and validation evidence.

Thanks,
Artem Dinaburg

 drivers/nvme/host/fabrics.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/nvme/host/fabrics.c b/drivers/nvme/host/fabrics.c
index fd01b86f10a4b0..8adcc8c97c42cf 100644
--- a/drivers/nvme/host/fabrics.c
+++ b/drivers/nvme/host/fabrics.c
@@ -179,7 +179,7 @@ int nvmf_reg_read32(struct nvme_ctrl *ctrl, u32 off, u32 *val)
 	cmd.prop_get.offset = cpu_to_le32(off);
 
 	ret = __nvme_submit_sync_cmd(ctrl->fabrics_q, &cmd, &res, NULL, 0,
-			NVME_QID_ANY, 0, 0);
+			NVME_QID_ANY, 0, BLK_MQ_REQ_RESERVED);
 
 	if (ret >= 0)
 		*val = le64_to_cpu(res.u64);
@@ -225,7 +225,7 @@ int nvmf_reg_read64(struct nvme_ctrl *ctrl, u32 off, u64 *val)
 	cmd.prop_get.offset = cpu_to_le32(off);
 
 	ret = __nvme_submit_sync_cmd(ctrl->fabrics_q, &cmd, &res, NULL, 0,
-			NVME_QID_ANY, 0, 0);
+			NVME_QID_ANY, 0, BLK_MQ_REQ_RESERVED);
 
 	if (ret >= 0)
 		*val = le64_to_cpu(res.u64);
@@ -270,7 +270,7 @@ int nvmf_reg_write32(struct nvme_ctrl *ctrl, u32 off, u32 val)
 	cmd.prop_set.value = cpu_to_le64(val);
 
 	ret = __nvme_submit_sync_cmd(ctrl->fabrics_q, &cmd, NULL, NULL, 0,
-			NVME_QID_ANY, 0, 0);
+			NVME_QID_ANY, 0, BLK_MQ_REQ_RESERVED);
 	if (unlikely(ret))
 		dev_err(ctrl->device,
 			"Property Set error: %d, offset %#x\n",
-- 
2.39.5