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From:   Fuad Tabba <tabba@google.com>
Date:   Wed, 1 Nov 2023 14:19:26 +0000
Message-ID: <CA+EHjTwEr4rLcs9VGQnhRKyBW7A_jGOjQe=zxYbmHnium5=W6Q@mail.gmail.com>
Subject: Re: [PATCH v13 08/35] KVM: Introduce KVM_SET_USER_MEMORY_REGION2
To:     Sean Christopherson <seanjc@google.com>
Cc:     Paolo Bonzini <pbonzini@redhat.com>, Marc Zyngier <maz@kernel.org>,
        Oliver Upton <oliver.upton@linux.dev>,
        Huacai Chen <chenhuacai@kernel.org>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Anup Patel <anup@brainfault.org>,
        Paul Walmsley <paul.walmsley@sifive.com>,
        Palmer Dabbelt <palmer@dabbelt.com>,
        Albert Ou <aou@eecs.berkeley.edu>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        Christian Brauner <brauner@kernel.org>,
        "Matthew Wilcox (Oracle)" <willy@infradead.org>,
        Andrew Morton <akpm@linux-foundation.org>, kvm@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev,
        linux-mips@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
        kvm-riscv@lists.infradead.org, linux-riscv@lists.infradead.org,
        linux-fsdevel@vger.kernel.org, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org, Xiaoyao Li <xiaoyao.li@intel.com>,
        Xu Yilun <yilun.xu@intel.com>,
        Chao Peng <chao.p.peng@linux.intel.com>,
        Jarkko Sakkinen <jarkko@kernel.org>,
        Anish Moorthy <amoorthy@google.com>,
        David Matlack <dmatlack@google.com>,
        Yu Zhang <yu.c.zhang@linux.intel.com>,
        Isaku Yamahata <isaku.yamahata@intel.com>,
        =?UTF-8?B?TWlja2HDq2wgU2FsYcO8bg==?= <mic@digikod.net>,
        Vlastimil Babka <vbabka@suse.cz>,
        Vishal Annapurve <vannapurve@google.com>,
        Ackerley Tng <ackerleytng@google.com>,
        Maciej Szmigiero <mail@maciej.szmigiero.name>,
        David Hildenbrand <david@redhat.com>,
        Quentin Perret <qperret@google.com>,
        Michael Roth <michael.roth@amd.com>,
        Wang <wei.w.wang@intel.com>,
        Liam Merwick <liam.merwick@oracle.com>,
        Isaku Yamahata <isaku.yamahata@gmail.com>,
        "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>
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On Fri, Oct 27, 2023 at 7:22=E2=80=AFPM Sean Christopherson <seanjc@google.=
com> 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@kernel.org>
> Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
> Reviewed-by: Xiaoyao Li <xiaoyao.li@intel.com>
> Signed-off-by: Sean Christopherson <seanjc@google.com>
> ---

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

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
>  =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
>
> 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 =3D 0; i < KVM_ADDRESS_SPACE_NUM; i++) {
> -               struct kvm_userspace_memory_region m;
> +               struct kvm_userspace_memory_region2 m;
>
>                 m.slot =3D id | (i << 16);
>                 m.flags =3D 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 *me=
m);
>  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 def=
ined
> @@ -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_regio=
n)
>  #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_regi=
on2)
>
>  /* 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_r=
egion *mem)
> +static int check_memory_region_flags(const struct kvm_userspace_memory_r=
egion2 *mem)
>  {
>         u32 valid_flags =3D KVM_MEM_LOG_DIRTY_PAGES;
>
> @@ -1980,7 +1980,7 @@ static bool kvm_check_memslot_overlap(struct kvm_me=
mslots *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 *me=
m)
>  {
>         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_reg=
ion *mem)
> +                                         struct kvm_userspace_memory_reg=
ion2 *mem)
>  {
>         if ((u16)mem->slot >=3D KVM_USER_MEM_SLOTS)
>                 return -EINVAL;
> @@ -4566,6 +4566,7 @@ static int kvm_vm_ioctl_check_extension_generic(str=
uct 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 *k=
vm)
>         return fd;
>  }
>
> +#define SANITY_CHECK_MEM_REGION_FIELD(field)                            =
       \
> +do {                                                                    =
       \
> +       BUILD_BUG_ON(offsetof(struct kvm_userspace_memory_region, field) =
!=3D             \
> +                    offsetof(struct kvm_userspace_memory_region2, field)=
);     \
> +       BUILD_BUG_ON(sizeof_field(struct kvm_userspace_memory_region, fie=
ld) !=3D         \
> +                    sizeof_field(struct kvm_userspace_memory_region2, fi=
eld)); \
> +} 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 =3D 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 =3D=3D KVM_SET_USER_MEMORY_REGION)
> +                       size =3D sizeof(struct kvm_userspace_memory_regio=
n);
> +               else
> +                       size =3D sizeof(struct kvm_userspace_memory_regio=
n2);
> +
> +               /* Ensure the common parts of the two structs are identic=
al. */
> +               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 =3D -EFAULT;
> -               if (copy_from_user(&kvm_userspace_mem, argp,
> -                                               sizeof(kvm_userspace_mem)=
))
> +               if (copy_from_user(&mem, argp, size))
>                         goto out;
>
> -               r =3D kvm_vm_ioctl_set_memory_region(kvm, &kvm_userspace_=
mem);
> +               r =3D kvm_vm_ioctl_set_memory_region(kvm, &mem);
>                 break;
>         }
>         case KVM_GET_DIRTY_LOG: {
> --
> 2.42.0.820.g83a721a137-goog
>