Re: [PATCH v13 08/35] KVM: Introduce KVM_SET_USER_MEMORY_REGION2

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On Fri, Oct 27, 2023 at 7:22 PM Sean Christopherson <seanjc@xxxxxxxxxx> wrote:
>
> Introduce a "version 2" of KVM_SET_USER_MEMORY_REGION so that additional
> information can be supplied without setting userspace up to fail.  The
> padding in the new kvm_userspace_memory_region2 structure will be used to
> pass a file descriptor in addition to the userspace_addr, i.e. allow
> userspace to point at a file descriptor and map memory into a guest that
> is NOT mapped into host userspace.
>
> Alternatively, KVM could simply add "struct kvm_userspace_memory_region2"
> without a new ioctl(), but as Paolo pointed out, adding a new ioctl()
> makes detection of bad flags a bit more robust, e.g. if the new fd field
> is guarded only by a flag and not a new ioctl(), then a userspace bug
> (setting a "bad" flag) would generate out-of-bounds access instead of an
> -EINVAL error.
>
> Cc: Jarkko Sakkinen <jarkko@xxxxxxxxxx>
> Reviewed-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> Reviewed-by: Xiaoyao Li <xiaoyao.li@xxxxxxxxx>
> Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
> ---

With the missing pad in api.rst fixed:
Reviewed-by: Fuad Tabba <tabba@xxxxxxxxxx>
Tested-by: Fuad Tabba <tabba@xxxxxxxxxx>

Cheers,
/fuad

>  Documentation/virt/kvm/api.rst | 21 +++++++++++++++++++
>  arch/x86/kvm/x86.c             |  2 +-
>  include/linux/kvm_host.h       |  4 ++--
>  include/uapi/linux/kvm.h       | 13 ++++++++++++
>  virt/kvm/kvm_main.c            | 38 +++++++++++++++++++++++++++-------
>  5 files changed, 67 insertions(+), 11 deletions(-)
>
> diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
> index 21a7578142a1..ace984acc125 100644
> --- a/Documentation/virt/kvm/api.rst
> +++ b/Documentation/virt/kvm/api.rst
> @@ -6070,6 +6070,27 @@ writes to the CNTVCT_EL0 and CNTPCT_EL0 registers using the SET_ONE_REG
>  interface. No error will be returned, but the resulting offset will not be
>  applied.
>
> +4.139 KVM_SET_USER_MEMORY_REGION2
> +---------------------------------
> +
> +:Capability: KVM_CAP_USER_MEMORY2
> +:Architectures: all
> +:Type: vm ioctl
> +:Parameters: struct kvm_userspace_memory_region2 (in)
> +:Returns: 0 on success, -1 on error
> +
> +::
> +
> +  struct kvm_userspace_memory_region2 {
> +       __u32 slot;
> +       __u32 flags;
> +       __u64 guest_phys_addr;
> +       __u64 memory_size; /* bytes */
> +       __u64 userspace_addr; /* start of the userspace allocated memory */
> +  };
> +
> +See KVM_SET_USER_MEMORY_REGION.
> +
>  5. The kvm_run structure
>  ========================
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 41cce5031126..6409914428ca 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -12455,7 +12455,7 @@ void __user * __x86_set_memory_region(struct kvm *kvm, int id, gpa_t gpa,
>         }
>
>         for (i = 0; i < KVM_ADDRESS_SPACE_NUM; i++) {
> -               struct kvm_userspace_memory_region m;
> +               struct kvm_userspace_memory_region2 m;
>
>                 m.slot = id | (i << 16);
>                 m.flags = 0;
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index 5faba69403ac..4e741ff27af3 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -1146,9 +1146,9 @@ enum kvm_mr_change {
>  };
>
>  int kvm_set_memory_region(struct kvm *kvm,
> -                         const struct kvm_userspace_memory_region *mem);
> +                         const struct kvm_userspace_memory_region2 *mem);
>  int __kvm_set_memory_region(struct kvm *kvm,
> -                           const struct kvm_userspace_memory_region *mem);
> +                           const struct kvm_userspace_memory_region2 *mem);
>  void kvm_arch_free_memslot(struct kvm *kvm, struct kvm_memory_slot *slot);
>  void kvm_arch_memslots_updated(struct kvm *kvm, u64 gen);
>  int kvm_arch_prepare_memory_region(struct kvm *kvm,
> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
> index 13065dd96132..bd1abe067f28 100644
> --- a/include/uapi/linux/kvm.h
> +++ b/include/uapi/linux/kvm.h
> @@ -95,6 +95,16 @@ struct kvm_userspace_memory_region {
>         __u64 userspace_addr; /* start of the userspace allocated memory */
>  };
>
> +/* for KVM_SET_USER_MEMORY_REGION2 */
> +struct kvm_userspace_memory_region2 {
> +       __u32 slot;
> +       __u32 flags;
> +       __u64 guest_phys_addr;
> +       __u64 memory_size;
> +       __u64 userspace_addr;
> +       __u64 pad[16];
> +};
> +
>  /*
>   * The bit 0 ~ bit 15 of kvm_userspace_memory_region::flags are visible for
>   * userspace, other bits are reserved for kvm internal use which are defined
> @@ -1192,6 +1202,7 @@ struct kvm_ppc_resize_hpt {
>  #define KVM_CAP_COUNTER_OFFSET 227
>  #define KVM_CAP_ARM_EAGER_SPLIT_CHUNK_SIZE 228
>  #define KVM_CAP_ARM_SUPPORTED_BLOCK_SIZES 229
> +#define KVM_CAP_USER_MEMORY2 230
>
>  #ifdef KVM_CAP_IRQ_ROUTING
>
> @@ -1473,6 +1484,8 @@ struct kvm_vfio_spapr_tce {
>                                         struct kvm_userspace_memory_region)
>  #define KVM_SET_TSS_ADDR          _IO(KVMIO,   0x47)
>  #define KVM_SET_IDENTITY_MAP_ADDR _IOW(KVMIO,  0x48, __u64)
> +#define KVM_SET_USER_MEMORY_REGION2 _IOW(KVMIO, 0x49, \
> +                                        struct kvm_userspace_memory_region2)
>
>  /* enable ucontrol for s390 */
>  struct kvm_s390_ucas_mapping {
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 6e708017064d..3f5b7c2c5327 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -1578,7 +1578,7 @@ static void kvm_replace_memslot(struct kvm *kvm,
>         }
>  }
>
> -static int check_memory_region_flags(const struct kvm_userspace_memory_region *mem)
> +static int check_memory_region_flags(const struct kvm_userspace_memory_region2 *mem)
>  {
>         u32 valid_flags = KVM_MEM_LOG_DIRTY_PAGES;
>
> @@ -1980,7 +1980,7 @@ static bool kvm_check_memslot_overlap(struct kvm_memslots *slots, int id,
>   * Must be called holding kvm->slots_lock for write.
>   */
>  int __kvm_set_memory_region(struct kvm *kvm,
> -                           const struct kvm_userspace_memory_region *mem)
> +                           const struct kvm_userspace_memory_region2 *mem)
>  {
>         struct kvm_memory_slot *old, *new;
>         struct kvm_memslots *slots;
> @@ -2084,7 +2084,7 @@ int __kvm_set_memory_region(struct kvm *kvm,
>  EXPORT_SYMBOL_GPL(__kvm_set_memory_region);
>
>  int kvm_set_memory_region(struct kvm *kvm,
> -                         const struct kvm_userspace_memory_region *mem)
> +                         const struct kvm_userspace_memory_region2 *mem)
>  {
>         int r;
>
> @@ -2096,7 +2096,7 @@ int kvm_set_memory_region(struct kvm *kvm,
>  EXPORT_SYMBOL_GPL(kvm_set_memory_region);
>
>  static int kvm_vm_ioctl_set_memory_region(struct kvm *kvm,
> -                                         struct kvm_userspace_memory_region *mem)
> +                                         struct kvm_userspace_memory_region2 *mem)
>  {
>         if ((u16)mem->slot >= KVM_USER_MEM_SLOTS)
>                 return -EINVAL;
> @@ -4566,6 +4566,7 @@ static int kvm_vm_ioctl_check_extension_generic(struct kvm *kvm, long arg)
>  {
>         switch (arg) {
>         case KVM_CAP_USER_MEMORY:
> +       case KVM_CAP_USER_MEMORY2:
>         case KVM_CAP_DESTROY_MEMORY_REGION_WORKS:
>         case KVM_CAP_JOIN_MEMORY_REGIONS_WORKS:
>         case KVM_CAP_INTERNAL_ERROR_DATA:
> @@ -4821,6 +4822,14 @@ static int kvm_vm_ioctl_get_stats_fd(struct kvm *kvm)
>         return fd;
>  }
>
> +#define SANITY_CHECK_MEM_REGION_FIELD(field)                                   \
> +do {                                                                           \
> +       BUILD_BUG_ON(offsetof(struct kvm_userspace_memory_region, field) !=             \
> +                    offsetof(struct kvm_userspace_memory_region2, field));     \
> +       BUILD_BUG_ON(sizeof_field(struct kvm_userspace_memory_region, field) !=         \
> +                    sizeof_field(struct kvm_userspace_memory_region2, field)); \
> +} while (0)
> +
>  static long kvm_vm_ioctl(struct file *filp,
>                            unsigned int ioctl, unsigned long arg)
>  {
> @@ -4843,15 +4852,28 @@ static long kvm_vm_ioctl(struct file *filp,
>                 r = kvm_vm_ioctl_enable_cap_generic(kvm, &cap);
>                 break;
>         }
> +       case KVM_SET_USER_MEMORY_REGION2:
>         case KVM_SET_USER_MEMORY_REGION: {
> -               struct kvm_userspace_memory_region kvm_userspace_mem;
> +               struct kvm_userspace_memory_region2 mem;
> +               unsigned long size;
> +
> +               if (ioctl == KVM_SET_USER_MEMORY_REGION)
> +                       size = sizeof(struct kvm_userspace_memory_region);
> +               else
> +                       size = sizeof(struct kvm_userspace_memory_region2);
> +
> +               /* Ensure the common parts of the two structs are identical. */
> +               SANITY_CHECK_MEM_REGION_FIELD(slot);
> +               SANITY_CHECK_MEM_REGION_FIELD(flags);
> +               SANITY_CHECK_MEM_REGION_FIELD(guest_phys_addr);
> +               SANITY_CHECK_MEM_REGION_FIELD(memory_size);
> +               SANITY_CHECK_MEM_REGION_FIELD(userspace_addr);
>
>                 r = -EFAULT;
> -               if (copy_from_user(&kvm_userspace_mem, argp,
> -                                               sizeof(kvm_userspace_mem)))
> +               if (copy_from_user(&mem, argp, size))
>                         goto out;
>
> -               r = kvm_vm_ioctl_set_memory_region(kvm, &kvm_userspace_mem);
> +               r = kvm_vm_ioctl_set_memory_region(kvm, &mem);
>                 break;
>         }
>         case KVM_GET_DIRTY_LOG: {
> --
> 2.42.0.820.g83a721a137-goog
>




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