Re: [RFC PATCH v12 06/33] KVM: Introduce KVM_SET_USER_MEMORY_REGION2

Xiaoyao Li <xiaoyao.li@xxxxxxxxx> · Fri, 15 Sep 2023 14:59:23 +0800

On 9/14/2023 9:55 AM, Sean Christopherson 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>
---
  arch/x86/kvm/x86.c       |  2 +-
  include/linux/kvm_host.h |  4 ++--
  include/uapi/linux/kvm.h | 13 +++++++++++++
  virt/kvm/kvm_main.c      | 38 ++++++++++++++++++++++++++++++--------
  4 files changed, 46 insertions(+), 11 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 6c9c81e82e65..8356907079e1 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -12447,7 +12447,7 @@ 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 8d21757cd5e9..7c0e38752526 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -1571,7 +1571,7 @@ 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;
  
@@ -1973,7 +1973,7 @@ 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;
@@ -2077,7 +2077,7 @@ 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;
  
@@ -2089,7 +2089,7 @@ 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;
@@ -4559,6 +4559,7 @@ 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:
@@ -4814,6 +4815,14 @@ 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)
  {
@@ -4836,15 +4845,28 @@ 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: {







