Re: [PATCH v7 02/16] iommu/smmu: Report empty domain nesting info

[Vivek Gautam <vivek.gautam@arm.com>]

Hi Yi,


On Thu, Sep 10, 2020 at 4:13 PM Liu Yi L <yi.l.liu@intel.com> wrote:
>
> This patch is added as instead of returning a boolean for DOMAIN_ATTR_NESTING,
> iommu_domain_get_attr() should return an iommu_nesting_info handle. For
> now, return an empty nesting info struct for now as true nesting is not
> yet supported by the SMMUs.
>
> Cc: Will Deacon <will@kernel.org>
> Cc: Robin Murphy <robin.murphy@arm.com>
> Cc: Eric Auger <eric.auger@redhat.com>
> Cc: Jean-Philippe Brucker <jean-philippe@linaro.org>
> Suggested-by: Jean-Philippe Brucker <jean-philippe@linaro.org>
> Signed-off-by: Liu Yi L <yi.l.liu@intel.com>
> Signed-off-by: Jacob Pan <jacob.jun.pan@linux.intel.com>
> Reviewed-by: Eric Auger <eric.auger@redhat.com>
> ---
> v5 -> v6:
> *) add review-by from Eric Auger.
>
> v4 -> v5:
> *) address comments from Eric Auger.
> ---
>  drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 29 +++++++++++++++++++++++++++--
>  drivers/iommu/arm/arm-smmu/arm-smmu.c       | 29 +++++++++++++++++++++++++++--
>  2 files changed, 54 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> index 7196207..016e2e5 100644
> --- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> +++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> @@ -3019,6 +3019,32 @@ static struct iommu_group *arm_smmu_device_group(struct device *dev)
>         return group;
>  }
>
> +static int arm_smmu_domain_nesting_info(struct arm_smmu_domain *smmu_domain,
> +                                       void *data)
> +{
> +       struct iommu_nesting_info *info = (struct iommu_nesting_info *)data;
> +       unsigned int size;
> +
> +       if (!info || smmu_domain->stage != ARM_SMMU_DOMAIN_NESTED)
> +               return -ENODEV;
> +
> +       size = sizeof(struct iommu_nesting_info);
> +
> +       /*
> +        * if provided buffer size is smaller than expected, should
> +        * return 0 and also the expected buffer size to caller.
> +        */
> +       if (info->argsz < size) {
> +               info->argsz = size;
> +               return 0;
> +       }
> +
> +       /* report an empty iommu_nesting_info for now */
> +       memset(info, 0x0, size);
> +       info->argsz = size;
> +       return 0;
> +}
> +
>  static int arm_smmu_domain_get_attr(struct iommu_domain *domain,
>                                     enum iommu_attr attr, void *data)
>  {
> @@ -3028,8 +3054,7 @@ static int arm_smmu_domain_get_attr(struct iommu_domain *domain,
>         case IOMMU_DOMAIN_UNMANAGED:
>                 switch (attr) {
>                 case DOMAIN_ATTR_NESTING:
> -                       *(int *)data = (smmu_domain->stage == ARM_SMMU_DOMAIN_NESTED);
> -                       return 0;
> +                       return arm_smmu_domain_nesting_info(smmu_domain, data);

Thanks for the patch.
This would unnecessarily overflow 'data' for any caller that's expecting only
an int data. Dump from one such issue that I was seeing when testing
this change along with local kvmtool changes is pasted below [1].

I could get around with the issue by adding another (iommu_attr) -
DOMAIN_ATTR_NESTING_INFO that returns (iommu_nesting_info).

Thanks & regards
Vivek

[1]--------------
[  811.756516] vfio-pci 0000:08:00.1: vfio_ecap_init: hiding ecap 0x1b@0x108
[  811.756516] Kernel panic - not syncing: stack-protector: Kernel
stack is corrupted in: vfio_pci_open+0x644/0x648
[  811.756516] CPU: 0 PID: 175 Comm: lkvm-cleanup-ne Not tainted
5.10.0-rc5-00096-gf015061e14cf #43
[  811.756516] Call trace:
[  811.756516]  dump_backtrace+0x0/0x1b0
[  811.756516]  show_stack+0x18/0x68
[  811.756516]  dump_stack+0xd8/0x134
[  811.756516]  panic+0x174/0x33c
[  811.756516]  __stack_chk_fail+0x3c/0x40
[  811.756516]  vfio_pci_open+0x644/0x648
[  811.756516]  vfio_group_fops_unl_ioctl+0x4bc/0x648
[  811.756516]  0x0
[  811.756516] SMP: stopping secondary CPUs
[  811.756597] Kernel Offset: disabled
[  811.756597] CPU features: 0x0040006,6a00aa38
[  811.756602] Memory Limit: none
[  811.768497] ---[ end Kernel panic - not syncing: stack-protector:
Kernel stack is corrupted in: vfio_pci_open+0x644/0x648 ]
-------------