Re: [PATCH v8 18/27] ARM: vITS: handle MAPD command

[Andre Przywara <andre.przywara@arm.com>]

Hi,

On 12/04/17 16:21, Julien Grall wrote:
> Hi Andre,
> 
> On 12/04/17 01:44, Andre Przywara wrote:
>> The MAPD command maps a device by associating a memory region for
>> storing ITEs with a certain device ID. Since it features a valid bit,
>> MAPD also covers the "unmap" functionality, which we also cover here.
>> We store the given guest physical address in the device table, and, if
>> this command comes from Dom0, tell the host ITS driver about this new
>> mapping, so it can issue the corresponding host MAPD command and create
>> the required tables. We take care of rolling back actions should one
>> step fail.
>> Upon unmapping a device we make sure we clean up all associated
>> resources and release the memory again.
>> We use our existing guest memory access function to find the right ITT
>> entry and store the mapping there (in guest memory).
>>
>> Signed-off-by: Andre Przywara <andre.przywara@arm.com>
>> ---
>>  xen/arch/arm/gic-v3-its.c        |  60 +++++++++++++++++
>>  xen/arch/arm/gic-v3-lpi.c        |  18 +++++
>>  xen/arch/arm/vgic-v3-its.c       | 137
>> +++++++++++++++++++++++++++++++++++++++
>>  xen/include/asm-arm/gic_v3_its.h |   6 ++
>>  4 files changed, 221 insertions(+)
>>
>> diff --git a/xen/arch/arm/gic-v3-its.c b/xen/arch/arm/gic-v3-its.c
>> index aebc257..900c9d1 100644
>> --- a/xen/arch/arm/gic-v3-its.c
>> +++ b/xen/arch/arm/gic-v3-its.c
>> @@ -800,6 +800,66 @@ out:
>>      return ret;
>>  }
>>
>> +/* Must be called with the its_device_lock held. */
>> +static struct its_device *get_its_device(struct domain *d, paddr_t
>> vdoorbell,
>> +                                          uint32_t vdevid)
>> +{
>> +    struct rb_node *node = d->arch.vgic.its_devices.rb_node;
>> +    struct its_device *dev;
>> +
>> +    ASSERT(spin_is_locked(&d->arch.vgic.its_devices_lock));
>> +
>> +    while (node)
>> +    {
>> +        int cmp;
>> +
>> +        dev = rb_entry(node, struct its_device, rbnode);
>> +        cmp = compare_its_guest_devices(dev, vdoorbell, vdevid);
>> +
>> +        if ( !cmp )
>> +            return dev;
>> +
>> +        if ( cmp > 0 )
>> +            node = node->rb_left;
>> +        else
>> +            node = node->rb_right;
>> +    }
>> +
>> +    return NULL;
>> +}
>> +
>> +static uint32_t get_host_lpi(struct its_device *dev, uint32_t eventid)
>> +{
>> +    uint32_t host_lpi = INVALID_LPI;
>> +
>> +    if ( dev && (eventid < dev->eventids) )
>> +        host_lpi = dev->host_lpi_blocks[eventid / LPI_BLOCK] +
>> +                                       (eventid % LPI_BLOCK);
>> +
>> +    return host_lpi;
>> +}
>> +
>> +int gicv3_remove_guest_event(struct domain *d, paddr_t
>> vdoorbell_address,
>> +                             uint32_t vdevid, uint32_t veventid)
>> +{
>> +    struct its_device *dev;
>> +    uint32_t host_lpi = INVALID_LPI;
>> +
>> +    spin_lock(&d->arch.vgic.its_devices_lock);
>> +    dev = get_its_device(d, vdoorbell_address, vdevid);
>> +    if ( dev && veventid <= dev->eventids )
>> +        host_lpi = get_host_lpi(dev, veventid);
>> +    spin_unlock(&d->arch.vgic.its_devices_lock);
>> +
>> +    if ( host_lpi == INVALID_LPI )
>> +        return -EINVAL;
>> +
>> +    gicv3_lpi_update_host_entry(host_lpi, d->domain_id,
>> +                                INVALID_VCPU_ID, INVALID_LPI);
>> +
>> +    return 0;
>> +}
>> +
>>  /* Scan the DT for any ITS nodes and create a list of host ITSes out
>> of it. */
>>  void gicv3_its_dt_init(const struct dt_device_node *node)
>>  {
>> diff --git a/xen/arch/arm/gic-v3-lpi.c b/xen/arch/arm/gic-v3-lpi.c
>> index 44f6315..d427539 100644
>> --- a/xen/arch/arm/gic-v3-lpi.c
>> +++ b/xen/arch/arm/gic-v3-lpi.c
>> @@ -207,6 +207,24 @@ out:
>>      irq_exit();
>>  }
>>
>> +void gicv3_lpi_update_host_entry(uint32_t host_lpi, int domain_id,
>> +                                 unsigned int vcpu_id, uint32_t
>> virt_lpi)
>> +{
>> +    union host_lpi *hlpip, hlpi;
>> +
>> +    ASSERT(host_lpi >= LPI_OFFSET);
>> +
>> +    host_lpi -= LPI_OFFSET;
>> +
>> +    hlpip = &lpi_data.host_lpis[host_lpi /
>> HOST_LPIS_PER_PAGE][host_lpi % HOST_LPIS_PER_PAGE];
>> +
>> +    hlpi.virt_lpi = virt_lpi;
>> +    hlpi.dom_id = domain_id;
>> +    hlpi.vcpu_id = vcpu_id;
>> +
>> +    write_u64_atomic(&hlpip->data, hlpi.data);
>> +}
>> +
>>  static int gicv3_lpi_allocate_pendtable(uint64_t *reg)
>>  {
>>      uint64_t val;
>> diff --git a/xen/arch/arm/vgic-v3-its.c b/xen/arch/arm/vgic-v3-its.c
>> index 6e505cb..104017e 100644
>> --- a/xen/arch/arm/vgic-v3-its.c
>> +++ b/xen/arch/arm/vgic-v3-its.c
>> @@ -52,6 +52,7 @@
>>   */
>>  struct virt_its {
>>      struct domain *d;
>> +    paddr_t doorbell_address;
>>      unsigned int devid_bits;
>>      unsigned int evid_bits;
>>      spinlock_t vcmd_lock;       /* Protects the virtual command
>> buffer, which */
>> @@ -166,6 +167,20 @@ static struct vcpu
>> *get_vcpu_from_collection(struct virt_its *its,
>>  #define DEV_TABLE_ENTRY(addr, bits)                     \
>>          (((addr) & GENMASK(51, 8)) | (((bits) - 1) & GENMASK(4, 0)))
>>
>> +/* Set the address of an ITT for a given device ID. */
>> +static int its_set_itt_address(struct virt_its *its, uint32_t devid,
>> +                               paddr_t itt_address, uint32_t nr_bits)
>> +{
>> +    paddr_t addr = get_baser_phys_addr(its->baser_dev);
>> +    uint64_t itt_entry = DEV_TABLE_ENTRY(itt_address, nr_bits);
>> +
>> +    if ( devid >= its->max_devices )
>> +        return -ENOENT;
>> +
>> +    return vgic_access_guest_memory(its->d, addr + devid *
>> sizeof(uint64_t),
>> +                                    &itt_entry, sizeof(itt_entry),
>> true);
>> +}
>> +
>>  /*
>>   * Lookup the address of the Interrupt Translation Table associated with
>>   * that device ID.
>> @@ -398,6 +413,125 @@ static int its_handle_mapc(struct virt_its *its,
>> uint64_t *cmdptr)
>>      return 0;
>>  }
>>
>> +/* Must be called with the ITS lock held. */
>> +static int its_discard_event(struct virt_its *its,
>> +                             uint32_t vdevid, uint32_t vevid)
>> +{
>> +    struct pending_irq *p;
>> +    unsigned long flags;
>> +    struct vcpu *vcpu;
>> +    uint32_t vlpi;
>> +
>> +    ASSERT(spin_is_locked(&its->its_lock));
>> +
>> +    if ( !read_itte_locked(its, vdevid, vevid, &vcpu, &vlpi) )
>> +        return -ENOENT;
>> +
>> +    if ( vlpi == INVALID_LPI )
>> +        return -ENOENT;
>> +
>> +    /* Lock this VCPU's VGIC to make sure nobody is using the
>> pending_irq. */
>> +    spin_lock_irqsave(&vcpu->arch.vgic.lock, flags);
> 
> There is an interesting issue happening with this code. You don't check
> the content of the memory provided by the guest. So a malicious guest
> could craft the memory in order to setup mapping with known vlpi and a
> different vCPU.
> 
> This would lead to use the wrong lock here and corrupt the list.

But this is true for basically most of the ITS table lookups. I added an
item to the cover letter to note this.

>> +
>> +    /* Remove the pending_irq from the tree. */
>> +    write_lock(&its->d->arch.vgic.pend_lpi_tree_lock);
>> +    p = radix_tree_delete(&its->d->arch.vgic.pend_lpi_tree, vlpi);
>> +    write_unlock(&its->d->arch.vgic.pend_lpi_tree_lock);
>> +
>> +    if ( !p )
>> +    {
>> +        spin_unlock_irqrestore(&vcpu->arch.vgic.lock, flags);
>> +
>> +        return -ENOENT;
>> +    }
>> +
>> +    /* Cleanup the pending_irq, to be reusable later. */
>> +    list_del_init(&p->inflight);
>> +    list_del_init(&p->lr_queue);
>> +    p->status = 0;
>> +    p->lr = GIC_INVALID_LR;
>> +    p->irq = INVALID_LPI;
> 
> Can't we have a generic helper to do that?

Added vgic_clear_pending_irq() next to vgic_init_pending_irq() in
vgic.c, if that is what you meant...

>> +
>> +    spin_unlock_irqrestore(&vcpu->arch.vgic.lock, flags);
>> +
>> +    /* Remove the corresponding host LPI entry */
>> +    return gicv3_remove_guest_event(its->d, its->doorbell_address,
>> +                                    vdevid, vevid);
>> +}
>> +
>> +static int its_unmap_device(struct virt_its *its, uint32_t devid)
>> +{
>> +    uint64_t itt, evid;
>> +    int ret;
>> +
>> +    spin_lock(&its->its_lock);
>> +
>> +    ret = its_get_itt(its, devid, &itt);
>> +    if ( ret )
>> +    {
>> +        spin_unlock(&its->its_lock);
>> +        return ret;
>> +    }
>> +
>> +    for ( evid = 0; evid < DEV_TABLE_ITT_SIZE(itt); evid++ )
>> +        /* Don't care about errors here, clean up as much as
>> possible. */
>> +        its_discard_event(its, devid, evid);
>> +
>> +    spin_unlock(&its->its_lock);
> 
> This code can be long to execute as the number of event can be huge. How
> do you plan to handle that?

It is assumed that DomUs get only a *very* limited and controlled number
of ITS resources, so the number of LPIs, number of devices and their
number of events will be very small, probably just enough as really
needed (event ID bits being 4 or so, for instance).

> *hint* this likely means a comment + ASSERT + TODO in the cover letter
> *hint*

Added.

>> +
>> +    return 0;
>> +}
>> +
>> +static int its_handle_mapd(struct virt_its *its, uint64_t *cmdptr)
>> +{
>> +    /* size and devid get validated by the functions called below. */
>> +    uint32_t devid = its_cmd_get_deviceid(cmdptr);
>> +    unsigned int size = its_cmd_get_size(cmdptr) + 1;
>> +    bool valid = its_cmd_get_validbit(cmdptr);
>> +    paddr_t itt_addr = its_cmd_get_ittaddr(cmdptr);
>> +    int ret;
>> +
>> +    /* Sanitize the number of events. */
>> +    if ( valid && (size > its->evid_bits) )
>> +        return -1;
>> +
>> +    /*
>> +     * There is no easy and clean way for Xen to know the ITS device
>> ID of a
>> +     * particular (PCI) device, so we have to rely on the guest telling
>> +     * us about it. For *now* we are just using the device ID *Dom0*
>> uses,
>> +     * because the driver there has the actual knowledge.
>> +     * Eventually this will be replaced with a dedicated hypercall to
>> +     * announce pass-through of devices.
>> +     */
>> +    if ( is_hardware_domain(its->d) )
>> +    {
>> +        if ( !valid )
>> +            /* Discard all events and remove pending LPIs. */
>> +            its_unmap_device(its, devid);
> 
> Likely, this call will have to be done for all the guests.

True.

>> +
>> +        /*
>> +         * Dom0's ITSes are mapped 1:1, so both addresses are the same.
>> +         * Also the device IDs are equal.
>> +         */
>> +        ret = gicv3_its_map_guest_device(its->d,
>> its->doorbell_address, devid,
>> +                                         its->doorbell_address, devid,
>> +                                         BIT(size), valid);
>> +        if ( ret && valid )
>> +            return ret;
>> +    }
>> +
>> +    spin_lock(&its->its_lock);
>> +
>> +    if ( valid )
>> +        ret = its_set_itt_address(its, devid, itt_addr, size);
>> +    else
>> +        ret = its_set_itt_address(its, devid, INVALID_PADDR, 1);
>> +
>> +    spin_unlock(&its->its_lock);
>> +
>> +    return ret;
>> +}
>> +
>>  #define ITS_CMD_BUFFER_SIZE(baser)      ((((baser) & 0xff) + 1) << 12)
>>  #define ITS_CMD_OFFSET(reg)             ((reg) & GENMASK(19, 5))
>>
>> @@ -436,6 +570,9 @@ static int vgic_its_handle_cmds(struct domain *d,
>> struct virt_its *its)
>>          case GITS_CMD_MAPC:
>>              ret = its_handle_mapc(its, command);
>>              break;
>> +        case GITS_CMD_MAPD:
>> +            ret = its_handle_mapd(its, command);
>> +            break;
>>          case GITS_CMD_SYNC:
>>              /* We handle ITS commands synchronously, so we ignore
>> SYNC. */
>>              break;
>> diff --git a/xen/include/asm-arm/gic_v3_its.h
>> b/xen/include/asm-arm/gic_v3_its.h
>> index 40f4ef5..60ffdb6 100644
>> --- a/xen/include/asm-arm/gic_v3_its.h
>> +++ b/xen/include/asm-arm/gic_v3_its.h
>> @@ -169,6 +169,12 @@ int gicv3_its_map_guest_device(struct domain *d,
>>  int gicv3_allocate_host_lpi_block(struct domain *d, uint32_t
>> *first_lpi);
>>  void gicv3_free_host_lpi_block(uint32_t first_lpi);
>>
>> +int gicv3_remove_guest_event(struct domain *d, paddr_t
>> vdoorbell_address,
>> +                                     uint32_t vdevid, uint32_t
>> veventid);
>> +
>> +void gicv3_lpi_update_host_entry(uint32_t host_lpi, int domain_id,
>> +                                 unsigned int vcpu_id, uint32_t
>> virt_lpi);
>> +
>>  #else
>>
>>  static inline void gicv3_its_dt_init(const struct dt_device_node *node)
>>
> 
> Cheers,
> 

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