Re: [PATCH v5 3/4] iommufd: Add IOMMU_GET_HW_INFO

[Baolu Lu]

On 2023/8/3 22:31, Yi Liu wrote:
> Under nested IOMMU translation, userspace owns the stage-1 translation
> table (e.g. the stage-1 page table of Intel VT-d or the context table
> of ARM SMMUv3, and etc.). Stage-1 translation tables are vendor specific,
> and need to be compatiable with the underlying IOMMU hardware. Hence,

                 compatible

> userspace should know the IOMMU hardware capability before creating and
> configuring the stage-1 translation table to kernel.
>
> This adds IOMMU_GET_HW_INFO ioctl to query the IOMMU hardware information
> (a.k.a capability) for a given device. The returned data is vendor specific,
> userspace needs to decode it with the structure mapped by the @out_data_type
> field.
>
> As only physical devices have IOMMU hardware, so this will return error
> if the given device is not a physical device.
>
> Co-developed-by: Nicolin Chen <nicolinc@xxxxxxxxxx>
> Signed-off-by: Nicolin Chen <nicolinc@xxxxxxxxxx>
> Signed-off-by: Yi Liu <yi.l.liu@xxxxxxxxx>
> ---
>   drivers/iommu/iommufd/main.c | 79 ++++++++++++++++++++++++++++++++++++
>   include/uapi/linux/iommufd.h | 36 ++++++++++++++++
>   2 files changed, 115 insertions(+)
>
> diff --git a/drivers/iommu/iommufd/main.c b/drivers/iommu/iommufd/main.c
> index 94c498b8fdf6..a0302bcaa97c 100644
> --- a/drivers/iommu/iommufd/main.c
> +++ b/drivers/iommu/iommufd/main.c
> @@ -17,6 +17,7 @@
>   #include <linux/bug.h>
>   #include <uapi/linux/iommufd.h>
>   #include <linux/iommufd.h>
> +#include "../iommu-priv.h"
>   
>   #include "io_pagetable.h"
>   #include "iommufd_private.h"
> @@ -177,6 +178,81 @@ static int iommufd_destroy(struct iommufd_ucmd *ucmd)
>   	return 0;
>   }
>   
> +static int iommufd_zero_fill_user(void __user *ptr, size_t bytes)
> +{
> +	int index = 0;
> +
> +	for (; index < bytes; index++) {
> +		if (put_user(0, (uint8_t __user *)(ptr + index)))
> +			return -EFAULT;
> +	}
> +	return 0;
> +}
> +
> +static int iommufd_get_hw_info(struct iommufd_ucmd *ucmd)
> +{
> +	u32 hw_info_type = IOMMU_HW_INFO_TYPE_NONE;
> +	struct iommu_hw_info *cmd = ucmd->cmd;
> +	unsigned int length = 0, data_len;
> +	struct iommufd_device *idev;
> +	const struct iommu_ops *ops;
> +	void __user *user_ptr;
> +	void *data = NULL;
> +	int rc = 0;
> +
> +	if (cmd->flags || cmd->__reserved || !cmd->data_len)
> +		return -EOPNOTSUPP;
> +
> +	idev = iommufd_get_device(ucmd, cmd->dev_id);
> +	if (IS_ERR(idev))
> +		return PTR_ERR(idev);
> +
> +	user_ptr = u64_to_user_ptr(cmd->data_ptr);
> +
> +	ops = dev_iommu_ops(idev->dev);
> +	if (!ops->hw_info)
> +		goto done;
> +
> +	data = ops->hw_info(idev->dev, &data_len, &hw_info_type);
> +	if (IS_ERR(data)) {
> +		rc = PTR_ERR(data);
> +		goto out_err;

Can kfree() handle a ERR_PTR input? I am afraid not,

/**
 * kfree - free previously allocated memory
 * @object: pointer returned by kmalloc() or kmem_cache_alloc()
 *
 * If @object is NULL, no operation is performed.
 */
void kfree(const void *object)
{
        struct folio *folio;
        struct slab *slab;
        struct kmem_cache *s;

        trace_kfree(_RET_IP_, object);

        if (unlikely(ZERO_OR_NULL_PTR(object)))
                return;

So, perhaps we should add

	data = NULL;

before
	goto out_err;

?

> +	}
> +
> +	/* driver has hw_info callback should have a unique hw_info_type */
> +	if (WARN_ON_ONCE(hw_info_type == IOMMU_HW_INFO_TYPE_NONE)) {
> +		rc = -ENODEV;
> +		goto out_err;
> +	}
> +
> +	length = min(cmd->data_len, data_len);
> +	if (copy_to_user(user_ptr, data, length)) {
> +		rc = -EFAULT;
> +		goto out_err;
> +	}
> +
> +done:
> +	/*
> +	 * Zero the trailing bytes if the user buffer is bigger than the
> +	 * data size kernel actually has.
> +	 */
> +	if (length < cmd->data_len) {
> +		rc = iommufd_zero_fill_user(user_ptr + length,
> +					    cmd->data_len - length);
> +		if (rc)
> +			goto out_err;
> +	}
> +
> +	cmd->data_len = length;
> +	cmd->out_data_type = hw_info_type;
> +	rc = iommufd_ucmd_respond(ucmd, sizeof(*cmd));
> +
> +out_err:
> +	kfree(data);
> +	iommufd_put_object(&idev->obj);
> +	return rc;
> +}
> +

Others look good to me, feel free to add:

Reviewed-by: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>

after above are addressed.

Best regards,
baolu