linux-kernel - Re: [PATCH v5 3/6] iommu/amd: Modify set_dte

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Message-ID: <20241007141756.GR1365916@nvidia.com>
Date: Mon, 7 Oct 2024 11:17:56 -0300
From: Jason Gunthorpe <jgg@...dia.com>
To: Suravee Suthikulpanit <suravee.suthikulpanit@....com>
Cc: linux-kernel@...r.kernel.org, iommu@...ts.linux.dev, joro@...tes.org,
	robin.murphy@....com, vasant.hegde@....com, kevin.tian@...el.com,
	jon.grimm@....com, santosh.shukla@....com, pandoh@...gle.com,
	kumaranand@...gle.com
Subject: Re: [PATCH v5 3/6] iommu/amd: Modify set_dte_entry() to use 256-bit
 DTE helpers

On Mon, Oct 07, 2024 at 04:13:50AM +0000, Suravee Suthikulpanit wrote:
> diff --git a/drivers/iommu/amd/iommu.c b/drivers/iommu/amd/iommu.c
> index deb19af48a3e..6fa2f5bb5156 100644
> --- a/drivers/iommu/amd/iommu.c
> +++ b/drivers/iommu/amd/iommu.c
> @@ -1956,90 +1956,114 @@ int amd_iommu_clear_gcr3(struct iommu_dev_data *dev_data, ioasid_t pasid)
>  	return ret;
>  }
>  
> +static void make_clear_dte(struct amd_iommu *iommu, struct dev_table_entry *dte,
> +			   struct dev_table_entry *new)
> +{
> +	new->data[0] = DTE_FLAG_V;
> +
> +	/* Apply erratum 63 */
> +	if (FIELD_GET(DTE_SYSMGT_MASK, dte->data[1]) == 0x01)
> +		new->data[0] |= BIT_ULL(DEV_ENTRY_IW);

Doesn't this need to be

/* Preserve set_dev_entry_from_acpi(), including erratum 64 */
new->data[1] |= dte->data[1] & DTE_SYSMGT_MASK;
if (FIELD_GET(DTE_SYSMGT_MASK, dte->data[1]) == 0x01)
   	new->data[0] |= BIT_ULL(DEV_ENTRY_IW);

And this has a significant security issue, we can't set IW here
because clear_dte must generate a blocked DTE, so TV=1,Mode=0,IW=1 is
not an OK setting!!

Jason