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

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Message-ID: <2f299f18-f828-4ca2-86ad-6f49eb2b485a@amd.com>
Date: Wed, 16 Oct 2024 12:15:27 +0700
From: "Suthikulpanit, Suravee" <suravee.suthikulpanit@....com>
To: Jason Gunthorpe <jgg@...dia.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 10/7/2024 9:17 PM, Jason Gunthorpe wrote:
> 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!!

I am reworking this part. I am going to introduce a variable in struct 
dev_data to store persistent value (during driver initialization) so 
that we can simply recreate the DTE from scratch w/o having to depend on 
existing configuration in the table. And it should address your concern 
regarding the IW bit during blocked DTE.

Suravee