[PATCH V2 0/3] dmaengine: idxd: Error path fixes

[PATCH V2 0/3] dmaengine: idxd: Error path fixes

[Reinette Chatre]

Changes since v1:
- V1: https://lore.kernel.org/lkml/cover.1670005163.git.reinette.chatre@intel.com/
- Cover trimmed after obtaining needed information.
- Added Reviewed-by tags.
- cc stable team.
- Please see individual patches for patch specific changes.

Dear Maintainers,

I have been using the IDXD driver to experiment with the upcoming core
changes in support of IMS ([1], [2], [3]). As part of this work I
happened to exercise the error paths within IDXD and encountered
a few issues that are addressed in this series. These changes are
independent from IMS and just aims to make the IDXD driver more
robust against errors.

Your feedback is greatly appreciated.

Reinette

[1] https://lore.kernel.org/lkml/20221111132706.104870257@linutronix.de
[2] https://lore.kernel.org/lkml/20221111131813.914374272@linutronix.dexo
[3] https://lore.kernel.org/lkml/20221111133158.196269823@linutronix.de

Reinette Chatre (3):
  dmaengine: idxd: Let probe fail when workqueue cannot be enabled
  dmaengine: idxd: Prevent use after free on completion memory
  dmaengine: idxd: Do not call DMX TX callbacks during workqueue disable

 drivers/dma/idxd/device.c | 16 +++++++++++++---
 1 file changed, 13 insertions(+), 3 deletions(-)


base-commit: 76dcd734eca23168cb008912c0f69ff408905235
-- 
2.34.1

[PATCH V2 1/3] dmaengine: idxd: Let probe fail when workqueue cannot be enabled

[Reinette Chatre]

The workqueue is enabled when the appropriate driver is loaded and
disabled when the driver is removed. When the driver is removed it
assumes that the workqueue was enabled successfully and proceeds to
free allocations made during workqueue enabling.

Failure during workqueue enabling does not prevent the driver from
being loaded. This is because the error path within drv_enable_wq()
returns success unless a second failure is encountered
during the error path. By returning success it is possible to load
the driver even if the workqueue cannot be enabled and
allocations that do not exist are attempted to be freed during
driver remove.

Some examples of problematic flows:
(a)

 idxd_dmaengine_drv_probe() -> drv_enable_wq() -> idxd_wq_request_irq():
 In above flow, if idxd_wq_request_irq() fails then
 idxd_wq_unmap_portal() is called on error exit path, but
 drv_enable_wq() returns 0 because idxd_wq_disable() succeeds. The
 driver is thus loaded successfully.

 idxd_dmaengine_drv_remove()->drv_disable_wq()->idxd_wq_unmap_portal()
 Above flow on driver unload triggers the WARN in devm_iounmap() because
 the device resource has already been removed during error path of
 drv_enable_wq().

(b)

 idxd_dmaengine_drv_probe() -> drv_enable_wq() -> idxd_wq_request_irq():
 In above flow, if idxd_wq_request_irq() fails then
 idxd_wq_init_percpu_ref() is never called to initialize the percpu
 counter, yet the driver loads successfully because drv_enable_wq()
 returns 0.

 idxd_dmaengine_drv_remove()->__idxd_wq_quiesce()->percpu_ref_kill():
 Above flow on driver unload triggers a BUG when attempting to drop the
 initial ref of the uninitialized percpu ref:
 BUG: kernel NULL pointer dereference, address: 0000000000000010

Fix the drv_enable_wq() error path by returning the original error that
indicates failure of workqueue enabling. This ensures that the probe
fails when an error is encountered and the driver remove paths are only
attempted when the workqueue was enabled successfully.

Fixes: 1f2bb40337f0 ("dmaengine: idxd: move wq_enable() to device.c")
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Reviewed-by: Dave Jiang <dave.jiang@intel.com>
Reviewed-by: Fenghua Yu <fenghua.yu@intel.com>
Cc: stable@vger.kernel.org
---
Changes since V1:
- Add Dave and Fenghua's Reviewed-by tags.
- Cc to stable team (Fenghua).

 drivers/dma/idxd/device.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/drivers/dma/idxd/device.c b/drivers/dma/idxd/device.c
index 6f44fa8f78a5..fcd03d29a941 100644
--- a/drivers/dma/idxd/device.c
+++ b/drivers/dma/idxd/device.c
@@ -1391,8 +1391,7 @@ int drv_enable_wq(struct idxd_wq *wq)
 err_irq:
 	idxd_wq_unmap_portal(wq);
 err_map_portal:
-	rc = idxd_wq_disable(wq, false);
-	if (rc < 0)
+	if (idxd_wq_disable(wq, false))
 		dev_dbg(dev, "wq %s disable failed\n", dev_name(wq_confdev(wq)));
 err:
 	return rc;
-- 
2.34.1

[PATCH V2 2/3] dmaengine: idxd: Prevent use after free on completion memory

[Reinette Chatre]

On driver unload any pending descriptors are flushed at the
time the interrupt is freed:
idxd_dmaengine_drv_remove() ->
	drv_disable_wq() ->
		idxd_wq_free_irq() ->
			idxd_flush_pending_descs().

If there are any descriptors present that need to be flushed this
flow triggers a "not present" page fault as below:

 BUG: unable to handle page fault for address: ff391c97c70c9040
 #PF: supervisor read access in kernel mode
 #PF: error_code(0x0000) - not-present page

The address that triggers the fault is the address of the
descriptor that was freed moments earlier via:
drv_disable_wq()->idxd_wq_free_resources()

Fix the use after free by freeing the descriptors after any possible
usage. This is done after idxd_wq_reset() to ensure that the memory
remains accessible during possible completion writes by the device.

Fixes: 63c14ae6c161 ("dmaengine: idxd: refactor wq driver enable/disable operations")
Suggested-by: Dave Jiang <dave.jiang@intel.com>
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Reviewed-by: Dave Jiang <dave.jiang@intel.com>
Reviewed-by: Fenghua Yu <fenghua.yu@intel.com>
Cc: stable@vger.kernel.org
---
Changes since V1:
- Add Dave and Fenghua's Reviewed-by tags.
- cc stable team (Fenghua).

 drivers/dma/idxd/device.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/dma/idxd/device.c b/drivers/dma/idxd/device.c
index fcd03d29a941..b4d7bb923a40 100644
--- a/drivers/dma/idxd/device.c
+++ b/drivers/dma/idxd/device.c
@@ -1408,11 +1408,11 @@ void drv_disable_wq(struct idxd_wq *wq)
 		dev_warn(dev, "Clients has claim on wq %d: %d\n",
 			 wq->id, idxd_wq_refcount(wq));
 
-	idxd_wq_free_resources(wq);
 	idxd_wq_unmap_portal(wq);
 	idxd_wq_drain(wq);
 	idxd_wq_free_irq(wq);
 	idxd_wq_reset(wq);
+	idxd_wq_free_resources(wq);
 	percpu_ref_exit(&wq->wq_active);
 	wq->type = IDXD_WQT_NONE;
 	wq->client_count = 0;
-- 
2.34.1

[PATCH V2 3/3] dmaengine: idxd: Do not call DMX TX callbacks during workqueue disable

[Reinette Chatre]

On driver unload any pending descriptors are flushed and pending
DMA descriptors are explicitly completed:
idxd_dmaengine_drv_remove() ->
	drv_disable_wq() ->
		idxd_wq_free_irq() ->
			idxd_flush_pending_descs() ->
				idxd_dma_complete_txd()

With this done during driver unload any remaining descriptor is
likely stuck and can be dropped. Even so, the descriptor may still
have a callback set that could no longer be accessible. An
example of such a problem is when the dmatest fails and the dmatest
module is unloaded. The failure of dmatest leaves descriptors with
dma_async_tx_descriptor::callback pointing to code that no longer
exist. This causes a page fault as below at the time the IDXD driver
is unloaded when it attempts to run the callback:
 BUG: unable to handle page fault for address: ffffffffc0665190
 #PF: supervisor instruction fetch in kernel mode
 #PF: error_code(0x0010) - not-present page

Fix this by clearing the callback pointers on the transmit
descriptors only when workqueue is disabled.

Fixes: 403a2e236538 ("dmaengine: idxd: change MSIX allocation based on per wq activation")
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Reviewed-by: Dave Jiang <dave.jiang@intel.com>
Reviewed-by: Fenghua Yu <fenghua.yu@intel.com>
Cc: stable@vger.kernel.org
---
Changes since V1:
- Add Dave and Fenghua's Reviewed-by tags.
- Cc stable team (Fenghua).
- Move declaration local to block needing it (Fenghua).
- Add appropriate Fixes tag (Fenghua).

 drivers/dma/idxd/device.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/drivers/dma/idxd/device.c b/drivers/dma/idxd/device.c
index b4d7bb923a40..6d8ff664fdfb 100644
--- a/drivers/dma/idxd/device.c
+++ b/drivers/dma/idxd/device.c
@@ -1173,8 +1173,19 @@ static void idxd_flush_pending_descs(struct idxd_irq_entry *ie)
 	spin_unlock(&ie->list_lock);
 
 	list_for_each_entry_safe(desc, itr, &flist, list) {
+		struct dma_async_tx_descriptor *tx;
+
 		list_del(&desc->list);
 		ctype = desc->completion->status ? IDXD_COMPLETE_NORMAL : IDXD_COMPLETE_ABORT;
+		/*
+		 * wq is being disabled. Any remaining descriptors are
+		 * likely to be stuck and can be dropped. callback could
+		 * point to code that is no longer accessible, for example
+		 * if dmatest module has been unloaded.
+		 */
+		tx = &desc->txd;
+		tx->callback = NULL;
+		tx->callback_result = NULL;
 		idxd_dma_complete_txd(desc, ctype, true);
 	}
 }
-- 
2.34.1

Re: [PATCH V2 0/3] dmaengine: idxd: Error path fixes

[Vinod Koul]

On 07-12-22, 14:52, Reinette Chatre wrote:
> Changes since v1:
> - V1: https://lore.kernel.org/lkml/cover.1670005163.git.reinette.chatre@intel.com/
> - Cover trimmed after obtaining needed information.
> - Added Reviewed-by tags.
> - cc stable team.
> - Please see individual patches for patch specific changes.
> 
> Dear Maintainers,
> 
> I have been using the IDXD driver to experiment with the upcoming core
> changes in support of IMS ([1], [2], [3]). As part of this work I
> happened to exercise the error paths within IDXD and encountered
> a few issues that are addressed in this series. These changes are
> independent from IMS and just aims to make the IDXD driver more
> robust against errors.
> 
> Your feedback is greatly appreciated.

Applied, thanks

-- 
~Vinod