Re: [PATCH v6 21/24] KVM: arm64: vgic-its: Device table save/restore

Auger Eric
2017-05-05T16:23:28Z

Hi Christoffer,

On 05/05/2017 14:44, Christoffer Dall wrote:
> On Thu, May 04, 2017 at 01:44:41PM +0200, Eric Auger wrote:
>> This patch saves the device table entries into guest RAM.
>> Both flat table and 2 stage tables are supported. DeviceId
>> indexing is used.
>>
>> For each device listed in the device table, we also save
>> the translation table using the vgic_its_save/restore_itt
>> routines. Those functions will be implemented in a subsequent
>> patch.
>>
>> On restore, devices are re-allocated and their itt are
>> re-built.
>>
>> Signed-off-by: Eric Auger <eric.auger@redhat.com>
>>
>> ---
>> v5 -> v6:
>> - accomodate vgic_its_alloc_device change of proto
>> - define bit fields for L1 entries
>> - s/handle_l1_entry/handle_l1_dte
>> - s/ite_esz/dte_esz in handle_l1_dte
>> - check BASER valid bit
>> - s/nb_eventid_bits/num_eventid_bits
>> - new convention for returned values
>> - itt functions implemented in subsequent patch
>>
>> v4 -> v5:
>> - sort the device list by deviceid on device table save
>> - use defines for shifts and masks
>> - use abi->dte_esz
>> - clatify entry sizes for L1 and L2 tables
>>
>> v3 -> v4:
>> - use the new proto for its_alloc_device
>> - compute_next_devid_offset, vgic_its_flush/restore_itt
>> become static in this patch
>> - change in the DTE entry format with the introduction of the
>> valid bit and next field width decrease; ittaddr encoded
>> on its full range
>> - fix handle_l1_entry entry handling
>> - correct vgic_its_table_restore error handling
>>
>> v2 -> v3:
>> - fix itt_addr bitmask in vgic_its_restore_dte
>> - addition of return 0 in vgic_its_restore_ite moved to
>> the ITE related patch
>>
>> v1 -> v2:
>> - use 8 byte format for DTE and ITE
>> - support 2 stage format
>> - remove kvm parameter
>> - ITT flush/restore moved in a separate patch
>> - use deviceid indexing
>> ---
>> virt/kvm/arm/vgic/vgic-its.c | 194 +++++++++++++++++++++++++++++++++++++++++--
>> virt/kvm/arm/vgic/vgic.h | 10 +++
>> 2 files changed, 199 insertions(+), 5 deletions(-)
>>
>> diff --git a/virt/kvm/arm/vgic/vgic-its.c b/virt/kvm/arm/vgic/vgic-its.c
>> index a3ed52a..c5b388d 100644
>> --- a/virt/kvm/arm/vgic/vgic-its.c
>> +++ b/virt/kvm/arm/vgic/vgic-its.c
>> @@ -23,6 +23,7 @@
>> #include <linux/interrupt.h>
>> #include <linux/list.h>
>> #include <linux/uaccess.h>
>> +#include <linux/list_sort.h>
>>
>> #include <linux/irqchip/arm-gic-v3.h>
>>
>> @@ -1701,7 +1702,8 @@ int vgic_its_attr_regs_access(struct kvm_device *dev,
>> return ret;
>> }
>>
>> -u32 compute_next_devid_offset(struct list_head *h, struct its_device *dev)
>> +static u32 compute_next_devid_offset(struct list_head *h,
>> + struct its_device *dev)
>> {
>> struct its_device *next;
>> u32 next_offset;
>> @@ -1755,8 +1757,8 @@ typedef int (*entry_fn_t)(struct vgic_its *its, u32 id, void *entry,
>> * Return: < 0 on error, 0 if last element was identified, 1 otherwise
>> * (the last element may not be found on second level tables)
>> */
>> -int scan_its_table(struct vgic_its *its, gpa_t base, int size, int esz,
>> - int start_id, entry_fn_t fn, void *opaque)
>> +static int scan_its_table(struct vgic_its *its, gpa_t base, int size, int esz,
>> + int start_id, entry_fn_t fn, void *opaque)
>> {
>> void *entry = kzalloc(esz, GFP_KERNEL);
>> struct kvm *kvm = its->dev->kvm;
>> @@ -1791,13 +1793,171 @@ int scan_its_table(struct vgic_its *its, gpa_t base, int size, int esz,
>> return ret;
>> }
>>
>> +static int vgic_its_save_itt(struct vgic_its *its, struct its_device *device)
>> +{
>> + return -ENXIO;
>> +}
>> +
>> +static int vgic_its_restore_itt(struct vgic_its *its, struct its_device *dev)
>> +{
>> + return -ENXIO;
>> +}
>> +
>> +/**
>> + * vgic_its_save_dte - Save a device table entry at a given GPA
>> + *
>> + * @its: ITS handle
>> + * @dev: ITS device
>> + * @ptr: GPA
>> + */
>> +static int vgic_its_save_dte(struct vgic_its *its, struct its_device *dev,
>> + gpa_t ptr, int dte_esz)
>> +{
>> + struct kvm *kvm = its->dev->kvm;
>> + u64 val, itt_addr_field;
>> + u32 next_offset;
>> +
>> + itt_addr_field = dev->itt_addr >> 8;
>> + next_offset = compute_next_devid_offset(&its->device_list, dev);
>> + val = (1ULL << KVM_ITS_DTE_VALID_SHIFT |
>> + ((u64)next_offset << KVM_ITS_DTE_NEXT_SHIFT) |
>> + (itt_addr_field << KVM_ITS_DTE_ITTADDR_SHIFT) |
>> + (dev->num_eventid_bits - 1));
>> + val = cpu_to_le64(val);
>> + return kvm_write_guest(kvm, ptr, &val, dte_esz);
>> +}
>> +
>> +/**
>> + * vgic_its_restore_dte - restore a device table entry
>> + *
>> + * @its: its handle
>> + * @id: device id the DTE corresponds to
>> + * @ptr: kernel VA where the 8 byte DTE is located
>> + * @opaque: unused
>> + *
>> + * Return: < 0 on error, 0 if the dte is the last one, id offset to the
>> + * next dte otherwise
>> + */
>> +static int vgic_its_restore_dte(struct vgic_its *its, u32 id,
>> + void *ptr, void *opaque)
>> +{
>> + struct its_device *dev;
>> + gpa_t itt_addr;
>> + u8 num_eventid_bits;
>> + u64 entry = *(u64 *)ptr;
>> + bool valid;
>> + u32 offset;
>> + int ret;
>> +
>> + entry = le64_to_cpu(entry);
>> +
>> + valid = entry >> KVM_ITS_DTE_VALID_SHIFT;
>> + num_eventid_bits = (entry & KVM_ITS_DTE_SIZE_MASK) + 1;
>> + itt_addr = ((entry & KVM_ITS_DTE_ITTADDR_MASK)
>> + >> KVM_ITS_DTE_ITTADDR_SHIFT) << 8;
>> +
>> + if (!valid)
>> + return 1;
>> +
>> + /* dte entry is valid */
>> + offset = (entry & KVM_ITS_DTE_NEXT_MASK) >> KVM_ITS_DTE_NEXT_SHIFT;
>> +
>> + dev = vgic_its_alloc_device(its, id, itt_addr, num_eventid_bits);
>> + if (IS_ERR(dev))
>> + return PTR_ERR(dev);
>> +
>> + ret = vgic_its_restore_itt(its, dev);
>> + if (ret)
>> + return ret;
>> +
>> + return offset;
>> +}
>> +
>> +static int vgic_its_device_cmp(void *priv, struct list_head *a,
>> + struct list_head *b)
>> +{
>> + struct its_device *deva = container_of(a, struct its_device, dev_list);
>> + struct its_device *devb = container_of(b, struct its_device, dev_list);
>> +
>> + if (deva->device_id < devb->device_id)
>> + return -1;
>> + else
>> + return 1;
>> +}
>> +
>> /**
>> * vgic_its_save_device_tables - Save the device table and all ITT
>> * into guest RAM
>> + *
>> + * L1/L2 handling is hidden by vgic_its_check_id() helper which directly
>> + * returns the GPA of the device entry
>> */
>> static int vgic_its_save_device_tables(struct vgic_its *its)
>> {
>> - return -ENXIO;
>> + const struct vgic_its_abi *abi = vgic_its_get_abi(its);
>> + struct its_device *dev;
>> + int dte_esz = abi->dte_esz;
>> + u64 baser;
>> +
>> + baser = its->baser_device_table;
>> +
>> + list_sort(NULL, &its->device_list, vgic_its_device_cmp);
>
> this list is protected by the ITS mutex but you seem to be only holding
> the KVM mutex here, so don't we have a potential exploit here?

Updates to the device, ite list are done when running commands. As we
hold the KVM mutex, commands cannot run. Then there is
vgic_its_destroy() which happens on kvm_put_kvm when all users have
released their reference. So to me holding the kvm lock looks sufficient.

Thanks

Eric

>
>
> Otherwise this patch looks good to me.
>
> Thanks,
> -Christoffer
>
>> +
>> + list_for_each_entry(dev, &its->device_list, dev_list) {
>> + int ret;
>> + gpa_t eaddr;
>> +
>> + if (!vgic_its_check_id(its, baser,
>> + dev->device_id, &eaddr))
>> + return -EINVAL;
>> +
>> + ret = vgic_its_save_itt(its, dev);
>> + if (ret)
>> + return ret;
>> +
>> + ret = vgic_its_save_dte(its, dev, eaddr, dte_esz);
>> + if (ret)
>> + return ret;
>> + }
>> + return 0;
>> +}
>> +
>> +/**
>> + * handle_l1_dte - callback used for L1 device table entries (2 stage case)
>> + *
>> + * @its: its handle
>> + * @id: index of the entry in the L1 table
>> + * @addr: kernel VA
>> + * @opaque: unused
>> + *
>> + * L1 table entries are scanned by steps of 1 entry
>> + * Return < 0 if error, 0 if last dte was found when scanning the L2
>> + * table, +1 otherwise (meaning next L1 entry must be scanned)
>> + */
>> +static int handle_l1_dte(struct vgic_its *its, u32 id, void *addr,
>> + void *opaque)
>> +{
>> + const struct vgic_its_abi *abi = vgic_its_get_abi(its);
>> + int l2_start_id = id * (SZ_64K / abi->dte_esz);
>> + u64 entry = *(u64 *)addr;
>> + int dte_esz = abi->dte_esz;
>> + gpa_t gpa;
>> + int ret;
>> +
>> + entry = le64_to_cpu(entry);
>> +
>> + if (!(entry & KVM_ITS_L1E_VALID_MASK))
>> + return 1;
>> +
>> + gpa = entry & KVM_ITS_L1E_ADDR_MASK;
>> +
>> + ret = scan_its_table(its, gpa, SZ_64K, dte_esz,
>> + l2_start_id, vgic_its_restore_dte, NULL);
>> +
>> + if (ret <= 0)
>> + return ret;
>> +
>> + return 1;
>> }
>>
>> /**
>> @@ -1806,7 +1966,31 @@ static int vgic_its_save_device_tables(struct vgic_its *its)
>> */
>> static int vgic_its_restore_device_tables(struct vgic_its *its)
>> {
>> - return -ENXIO;
>> + const struct vgic_its_abi *abi = vgic_its_get_abi(its);
>> + u64 baser = its->baser_device_table;
>> + int l1_esz, ret;
>> + int l1_tbl_size = GITS_BASER_NR_PAGES(baser) * SZ_64K;
>> + gpa_t l1_gpa;
>> +
>> + if (!(baser & GITS_BASER_VALID))
>> + return 0;
>> +
>> + l1_gpa = BASER_ADDRESS(baser);
>> +
>> + if (baser & GITS_BASER_INDIRECT) {
>> + l1_esz = GITS_LVL1_ENTRY_SIZE;
>> + ret = scan_its_table(its, l1_gpa, l1_tbl_size, l1_esz, 0,
>> + handle_l1_dte, NULL);
>> + } else {
>> + l1_esz = abi->dte_esz;
>> + ret = scan_its_table(its, l1_gpa, l1_tbl_size, l1_esz, 0,
>> + vgic_its_restore_dte, NULL);
>> + }
>> +
>> + if (ret > 0)
>> + ret = -EINVAL;
>> +
>> + return ret;
>> }
>>
>> static int vgic_its_save_cte(struct vgic_its *its,
>> diff --git a/virt/kvm/arm/vgic/vgic.h b/virt/kvm/arm/vgic/vgic.h
>> index 58adcae..e896114 100644
>> --- a/virt/kvm/arm/vgic/vgic.h
>> +++ b/virt/kvm/arm/vgic/vgic.h
>> @@ -81,6 +81,16 @@
>> #define KVM_ITS_CTE_VALID_MASK BIT_ULL(63)
>> #define KVM_ITS_CTE_RDBASE_SHIFT 16
>> #define KVM_ITS_CTE_ICID_MASK GENMASK_ULL(15, 0)
>> +#define KVM_ITS_DTE_VALID_SHIFT 63
>> +#define KVM_ITS_DTE_VALID_MASK BIT_ULL(63)
>> +#define KVM_ITS_DTE_NEXT_SHIFT 49
>> +#define KVM_ITS_DTE_NEXT_MASK GENMASK_ULL(62, 49)
>> +#define KVM_ITS_DTE_ITTADDR_SHIFT 5
>> +#define KVM_ITS_DTE_ITTADDR_MASK GENMASK_ULL(48, 5)
>> +#define KVM_ITS_DTE_SIZE_MASK GENMASK_ULL(4, 0)
>> +#define KVM_ITS_L1E_VALID_MASK BIT_ULL(63)
>> +/* we only support 64 kB translation table page size */
>> +#define KVM_ITS_L1E_ADDR_MASK GENMASK_ULL(51, 16)
>>
>> static inline bool irq_is_pending(struct vgic_irq *irq)
>> {
>> --
>> 2.5.5
>>
>
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