Re: [PATCH v2] iommu/vt-d: Fix PASID directory pointer coherency

[Jacob Pan]

Hi Baolu,

On Wed, 8 Feb 2023 11:46:37 +0800, Baolu Lu <baolu.lu@xxxxxxxxxxxxxxx>
wrote:

> On 2023/2/8 8:09, Jacob Pan wrote:
> > On platforms that do not support IOMMU Extended capability bit 0
> > Page-walk Coherency, CPU caches are not snooped when IOMMU is accessing
> > any translation structures. IOMMU access goes only directly to
> > memory. Intel IOMMU code was missing a flush for the PASID table
> > directory that resulted in the unrecoverable fault as shown below.
> > 
> > This patch adds clflush calls whenever activating and updating
> > a PASID table directory to ensure cache coherency.
> > 
> > On the reverse direction, there's no need to clflush the PASID directory
> > pointer when we deactivate a context entry in that IOMMU hardware will
> > not see the old PASID directory pointer after we clear the context
> > entry. PASID directory entries are also never freed once allocated.
> > 
> > [    0.555386] DMAR: DRHD: handling fault status reg 3
> > [    0.555805] DMAR: [DMA Read NO_PASID] Request device [00:0d.2] fault
> > addr 0x1026a4000 [fault reason 0x51] SM: Present bit in Directory Entry
> > is clear [    0.556348] DMAR: Dump dmar1 table entries for IOVA
> > 0x1026a4000 [    0.556348] DMAR: scalable mode root entry: hi
> > 0x0000000102448001, low 0x0000000101b3e001 [    0.556348] DMAR: context
> > entry: hi 0x0000000000000000, low 0x0000000101b4d401 [    0.556348]
> > DMAR: pasid dir entry: 0x0000000101b4e001 [    0.556348] DMAR: pasid
> > table entry[0]: 0x0000000000000109 [    0.556348] DMAR: pasid table
> > entry[1]: 0x0000000000000001 [    0.556348] DMAR: pasid table entry[2]:
> > 0x0000000000000000 [    0.556348] DMAR: pasid table entry[3]:
> > 0x0000000000000000 [    0.556348] DMAR: pasid table entry[4]:
> > 0x0000000000000000 [    0.556348] DMAR: pasid table entry[5]:
> > 0x0000000000000000 [    0.556348] DMAR: pasid table entry[6]:
> > 0x0000000000000000 [    0.556348] DMAR: pasid table entry[7]:
> > 0x0000000000000000 [    0.556348] DMAR: PTE not present at level 4
> > 
> > Cc:<stable@xxxxxxxxxxxxxxx>
> > Fixes: 0bbeb01a4faf ("iommu/vt-d: Manage scalalble mode PASID tables")
> > Reported-by: Sukumar Ghorai<sukumar.ghorai@xxxxxxxxx>
> > Signed-off-by: Ashok Raj<ashok.raj@xxxxxxxxx>
> > Signed-off-by: Jacob Pan<jacob.jun.pan@xxxxxxxxxxxxxxx>
> > ---
> > v2: Add clflush to PASID directory update case (Baolu, Kevin review)
> > ---
> >   drivers/iommu/intel/iommu.c | 2 ++
> >   drivers/iommu/intel/pasid.c | 2 ++
> >   2 files changed, 4 insertions(+)
> > 
> > diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
> > index 59df7e42fd53..161342e7149d 100644
> > --- a/drivers/iommu/intel/iommu.c
> > +++ b/drivers/iommu/intel/iommu.c
> > @@ -1976,6 +1976,8 @@ static int domain_context_mapping_one(struct
> > dmar_domain *domain, pds = context_get_sm_pds(table);
> >   		context->lo = (u64)virt_to_phys(table->table) |
> >   				context_pdts(pds);
> > +		if (!ecap_coherent(iommu->ecap))
> > +			clflush_cache_range(table->table,
> > sizeof(u64));  
> 
> This leaves other pasid dir entries not clflush'ed. It is possible that
> IOMMU hardware sees different value from what CPU has set. This may
> leave security holes for malicious devices. It's same to the pasid entry
> table.
agreed, we need to address security and functional aspects. good point.

thanks

Jacob

> How about below change? It does clflush whenever CPU changes the pasid
> dir/entry tables.
> 
> diff --git a/drivers/iommu/intel/pasid.c b/drivers/iommu/intel/pasid.c
> index fb3c7020028d..aeb0517826a2 100644
> --- a/drivers/iommu/intel/pasid.c
> +++ b/drivers/iommu/intel/pasid.c
> @@ -128,6 +128,9 @@ int intel_pasid_alloc_table(struct device *dev)
>          pasid_table->max_pasid = 1 << (order + PAGE_SHIFT + 3);
>          info->pasid_table = pasid_table;
> 
> +       if (!ecap_coherent(info->iommu->ecap))
> +               clflush_cache_range(pasid_table->table, size);
> +
>          return 0;
>   }
> 
> @@ -215,6 +218,11 @@ static struct pasid_entry 
> *intel_pasid_get_entry(struct device *dev, u32 pasid)
>                          free_pgtable_page(entries);
>                          goto retry;
>                  }
> +
> +               if (!ecap_coherent(info->iommu->ecap)) {
> +                       clflush_cache_range(entries, VTD_PAGE_SIZE);
> +                       clflush_cache_range(&dir[dir_index].val, 
> sizeof(*dir));
> +               }
>          }
> 
>          return &entries[index];
> 
> Best regards,
> baolu


Thanks,

Jacob