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

Christoffer Dall
2017-05-05T12:44:27Z

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?

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
>