KVM: Introduce KVM_SET_USER_MEMORY_REGION2

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>
Reviewed-by: Fuad Tabba <tabba@google.com>
Tested-by: Fuad Tabba <tabba@google.com>
Message-Id: <20231027182217.3615211-9-seanjc@google.com>
Acked-by: Kai Huang <kai.huang@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
index 7025b37510279530058dc68f66a1140fd72458a5..9edd9e436bab4aa3194155d9ed48a26a7aa9f1dc 100644 (file)
--- a/Documentation/virt/kvm/api.rst
+++ b/Documentation/virt/kvm/api.rst
@@ -6192,6 +6192,28 @@ to know what fields can be changed for the system register described by
 ``op0, op1, crn, crm, op2``. KVM rejects ID register values that describe a
 superset of the features supported by the system.
 
+4.140 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 */
+       __u64 pad[16];
+  };
+
+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 2c924075f6f112a594c0a4390bb7dcc2d7e8fabf..7b389f27dffcae22d22384845f5b24ae028378de 100644 (file)
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -12576,7 +12576,7 @@ 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 5faba69403ac49f1d258f75bb289753ca3e82a6a..4e741ff27af36fc309308bcfaedd6b53f3f5f3c6 100644 (file)
--- 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 211b86de35ac53f6457bbd2fae8c973ce6b3a968..308cc70bd6ab86080183b4e9cce905e75b936481 100644 (file)
--- 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
@@ -1201,6 +1211,7 @@ struct kvm_ppc_resize_hpt {
 #define KVM_CAP_ARM_EAGER_SPLIT_CHUNK_SIZE 228
 #define KVM_CAP_ARM_SUPPORTED_BLOCK_SIZES 229
 #define KVM_CAP_ARM_SUPPORTED_REG_MASK_RANGES 230
+#define KVM_CAP_USER_MEMORY2 231
 
 #ifdef KVM_CAP_IRQ_ROUTING
 
@@ -1483,6 +1494,8 @@ 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 dc81279ea385017e0e1c77424e432929f701949a..756b94ecd5110a0dd7994fa65cca4520c3ee41d0 100644 (file)
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -1580,7 +1580,15 @@ static void kvm_replace_memslot(struct kvm *kvm,
        }
 }
 
-static int check_memory_region_flags(const struct kvm_userspace_memory_region *mem)
+/*
+ * Flags that do not access any of the extra space of struct
+ * kvm_userspace_memory_region2.  KVM_SET_USER_MEMORY_REGION_V1_FLAGS
+ * only allows these.
+ */
+#define KVM_SET_USER_MEMORY_REGION_V1_FLAGS \
+       (KVM_MEM_LOG_DIRTY_PAGES | KVM_MEM_READONLY)
+
+static int check_memory_region_flags(const struct kvm_userspace_memory_region2 *mem)
 {
        u32 valid_flags = KVM_MEM_LOG_DIRTY_PAGES;
 
@@ -1982,7 +1990,7 @@ 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;
@@ -2086,7 +2094,7 @@ 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;
 
@@ -2098,7 +2106,7 @@ 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;
@@ -4568,6 +4576,7 @@ 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:
@@ -4823,6 +4832,14 @@ 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)
 {
@@ -4845,15 +4862,39 @@ 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) {
+                       /*
+                        * Fields beyond struct kvm_userspace_memory_region shouldn't be
+                        * accessed, but avoid leaking kernel memory in case of a bug.
+                        */
+                       memset(&mem, 0, sizeof(mem));
+                       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 = -EINVAL;
+               if (ioctl == KVM_SET_USER_MEMORY_REGION &&
+                   (mem.flags & ~KVM_SET_USER_MEMORY_REGION_V1_FLAGS))
                        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: {