[PATCH] dmaengine: idxd: Do not enable user type Work Queue without Shared Virtual Addressing
Userspace can directly access physical address through user type Work Queue (WQ) in two scenarios: no IOMMU or IOMMU Passthrough without Shared Virtual Addressing (SVA). In these two cases, user type WQ allows userspace to issue DMA physical address access without virtual to physical translation.
This is inconsistent with the security goals of a good kernel API.
Plus there is no usage for user type WQ without SVA.
So enable user type WQ only when SVA is enabled (i.e. user PASID is enabled).
Fixes: 42d279f9137a ("dmaengine: idxd: add char driver to expose submission portal to userland")
Suggested-by: Arjan Van De Ven arjan.van.de.ven@intel.com Signed-off-by: Fenghua Yu fenghua.yu@intel.com Reviewed-by: Dave Jiang dave.jiang@intel.com --- drivers/dma/idxd/cdev.c | 14 ++++++++++++++ include/uapi/linux/idxd.h | 1 + 2 files changed, 15 insertions(+)
diff --git a/drivers/dma/idxd/cdev.c b/drivers/dma/idxd/cdev.c index c2808fd081d6..4cd3400c5a48 100644 --- a/drivers/dma/idxd/cdev.c +++ b/drivers/dma/idxd/cdev.c @@ -312,6 +312,20 @@ static int idxd_user_drv_probe(struct idxd_dev *idxd_dev) if (idxd->state != IDXD_DEV_ENABLED) return -ENXIO;
+ /* + * User type WQ is enabled only when SVA is enabled for two reasons: + * - If no IOMMU or IOMMU Passthrough without SVA, userspace + * can directly access physical address through the WQ. + * - There is no usage case for the WQ without SVA. + */ + if (!device_user_pasid_enabled(idxd)) { + idxd->cmd_status = IDXD_SCMD_WQ_USER_NO_IOMMU; + dev_dbg(&idxd->pdev->dev, + "User type WQ cannot be enabled without SVA.\n"); + + return -EOPNOTSUPP; + } + mutex_lock(&wq->wq_lock); wq->type = IDXD_WQT_USER; rc = drv_enable_wq(wq); diff --git a/include/uapi/linux/idxd.h b/include/uapi/linux/idxd.h index 095299c75828..2b9e7feba3f3 100644 --- a/include/uapi/linux/idxd.h +++ b/include/uapi/linux/idxd.h @@ -29,6 +29,7 @@ enum idxd_scmd_stat { IDXD_SCMD_WQ_NO_SIZE = 0x800e0000, IDXD_SCMD_WQ_NO_PRIV = 0x800f0000, IDXD_SCMD_WQ_IRQ_ERR = 0x80100000, + IDXD_SCMD_WQ_USER_NO_IOMMU = 0x80110000, };
#define IDXD_SCMD_SOFTERR_MASK 0x80000000
Hi,
Thanks for your patch.
FYI: kernel test robot notices the stable kernel rule is not satisfied.
Rule: 'Cc: stable@vger.kernel.org' or 'commit <sha1> upstream.' Subject: [PATCH] dmaengine: idxd: Do not enable user type Work Queue without Shared Virtual Addressing Link: https://lore.kernel.org/stable/20221012201418.3883096-1-fenghua.yu%40intel.c...
The check is based on https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html
On 10/12/22 13:14, Fenghua Yu wrote:
Userspace can directly access physical address through user type Work Queue (WQ) in two scenarios: no IOMMU or IOMMU Passthrough without Shared Virtual Addressing (SVA). In these two cases, user type WQ allows userspace to issue DMA physical address access without virtual to physical translation.
This is inconsistent with the security goals of a good kernel API.
Plus there is no usage for user type WQ without SVA.
So enable user type WQ only when SVA is enabled (i.e. user PASID is enabled).
I'm not sure the changelog here is great.
The whole "user Work Queue" thing is an entire *DRIVER*. So, this really has zero to do with the type of workqueue and everything to do with the kind of drivers we allow to be loaded and drive the hardware.
Basically, the *hardware* allows pretty arbitrary direct access to physical memory. The 'idxd_user_drv' driver code (including idxd_user_drv_probe()) gives low-level, direct access to the hardware, which is bad news.
Plus, even if userspace got access to the device via this driver, they have to feel physical addresses to it, which is generally not easy from userspace.
That's as close as I can get to rephrasing the above TLA soup in plain old English.
I also detest the "There is no usage case for the WQ without SVA." language. Those words lack meaning. There has to be a *REASON* there is no use case. Please think about what those words *mean*, then delete them and write what they mean.
Hi, Dave,
On 10/12/22 14:14, Dave Hansen wrote:
On 10/12/22 13:14, Fenghua Yu wrote:
Userspace can directly access physical address through user type Work Queue (WQ) in two scenarios: no IOMMU or IOMMU Passthrough without Shared Virtual Addressing (SVA). In these two cases, user type WQ allows userspace to issue DMA physical address access without virtual to physical translation.
This is inconsistent with the security goals of a good kernel API.
Plus there is no usage for user type WQ without SVA.
So enable user type WQ only when SVA is enabled (i.e. user PASID is enabled).
I'm not sure the changelog here is great.
The whole "user Work Queue" thing is an entire *DRIVER*. So, this really has zero to do with the type of workqueue and everything to do with the kind of drivers we allow to be loaded and drive the hardware.
Basically, the *hardware* allows pretty arbitrary direct access to physical memory. The 'idxd_user_drv' driver code (including idxd_user_drv_probe()) gives low-level, direct access to the hardware, which is bad news.
Plus, even if userspace got access to the device via this driver, they have to feel physical addresses to it, which is generally not easy from userspace.
That's as close as I can get to rephrasing the above TLA soup in plain old English.
I also detest the "There is no usage case for the WQ without SVA." language. Those words lack meaning. There has to be a *REASON* there is no use case. Please think about what those words *mean*, then delete them and write what they mean.
I'm working on changing the changelog and will send v2 with the changes.
Thanks.
-Fenghua
linux-stable-mirror@lists.linaro.org
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Dave Hansen -
Fenghua Yu -
kernel test robot -
Yu, Fenghua