diff mbox series

[v5,06/13] KVM: Use kvm_userspace_memory_region_ext

Message ID 20220310140911.50924-7-chao.p.peng@linux.intel.com
State New
Headers show
Series KVM: mm: fd-based approach for supporting KVM guest private memory | expand

Commit Message

Chao Peng March 10, 2022, 2:09 p.m. UTC 
Use the new extended memslot structure kvm_userspace_memory_region_ext.
The extended part (private_fd/ private_offset) will be copied from
userspace only when KVM_MEM_PRIVATE is set. Internally old
kvm_userspace_memory_region will still be used for places where the
extended fields are not needed.

Signed-off-by: Yu Zhang <yu.c.zhang@linux.intel.com>
Signed-off-by: Chao Peng <chao.p.peng@linux.intel.com>
---
 arch/x86/kvm/x86.c       | 12 ++++++------
 include/linux/kvm_host.h |  4 ++--
 virt/kvm/kvm_main.c      | 30 ++++++++++++++++++++----------
 3 files changed, 28 insertions(+), 18 deletions(-)

Comments

Sean Christopherson March 28, 2022, 10:26 p.m. UTC | #1 
On Thu, Mar 10, 2022, Chao Peng wrote:
> @@ -4476,14 +4477,23 @@ static long kvm_vm_ioctl(struct file *filp,
>  		break;
>  	}
>  	case KVM_SET_USER_MEMORY_REGION: {
> -		struct kvm_userspace_memory_region kvm_userspace_mem;
> +		struct kvm_userspace_memory_region_ext region_ext;

It's probably a good idea to zero initialize the full region to avoid consuming
garbage stack data if there's a bug and an _ext field is accessed without first
checking KVM_MEM_PRIVATE.  I'm usually opposed to unnecessary initialization, but
this seems like something we could screw up quite easily.

>  		r = -EFAULT;
> -		if (copy_from_user(&kvm_userspace_mem, argp,
> -						sizeof(kvm_userspace_mem)))
> +		if (copy_from_user(&region_ext, argp,
> +				sizeof(struct kvm_userspace_memory_region)))
>  			goto out;
> +		if (region_ext.region.flags & KVM_MEM_PRIVATE) {
> +			int offset = offsetof(
> +				struct kvm_userspace_memory_region_ext,
> +				private_offset);
> +			if (copy_from_user(&region_ext.private_offset,
> +					   argp + offset,
> +					   sizeof(region_ext) - offset))

In this patch, KVM_MEM_PRIVATE should result in an -EINVAL as it's not yet
supported.  Copying the _ext on KVM_MEM_PRIVATE belongs in the "Expose KVM_MEM_PRIVATE"
patch.

Mechnically, what about first reading flags via get_user(), and then doing a single
copy_from_user()?  It's technically more work in the common case, and requires an
extra check to guard against TOCTOU attacks, but this isn't a fast path by any means
and IMO the end result makes it easier to understand the relationship between
KVM_MEM_PRIVATE and the two different structs.

E.g.

	case KVM_SET_USER_MEMORY_REGION: {
		struct kvm_user_mem_region region;
		unsigned long size;
		u32 flags;

		memset(&region, 0, sizeof(region));

		r = -EFAULT;
		if (get_user(flags, (u32 __user *)(argp + offsetof(typeof(region), flags))))
			goto out;

		if (flags & KVM_MEM_PRIVATE)
			size = sizeof(struct kvm_userspace_memory_region_ext);
		else
			size = sizeof(struct kvm_userspace_memory_region);
		if (copy_from_user(&region, argp, size))
			goto out;

		r = -EINVAL;
		if ((flags ^ region.flags) & KVM_MEM_PRIVATE)
			goto out;

		r = kvm_vm_ioctl_set_memory_region(kvm, &region);
		break;
	}

> +				goto out;
> +		}
>  
> -		r = kvm_vm_ioctl_set_memory_region(kvm, &kvm_userspace_mem);
> +		r = kvm_vm_ioctl_set_memory_region(kvm, &region_ext);
>  		break;
>  	}
>  	case KVM_GET_DIRTY_LOG: {
> -- 
> 2.17.1
>
Chao Peng April 8, 2022, 1:58 p.m. UTC | #2 
On Mon, Mar 28, 2022 at 10:26:55PM +0000, Sean Christopherson wrote:
> On Thu, Mar 10, 2022, Chao Peng wrote:
> > @@ -4476,14 +4477,23 @@ static long kvm_vm_ioctl(struct file *filp,
> >  		break;
> >  	}
> >  	case KVM_SET_USER_MEMORY_REGION: {
> > -		struct kvm_userspace_memory_region kvm_userspace_mem;
> > +		struct kvm_userspace_memory_region_ext region_ext;
> 
> It's probably a good idea to zero initialize the full region to avoid consuming
> garbage stack data if there's a bug and an _ext field is accessed without first
> checking KVM_MEM_PRIVATE.  I'm usually opposed to unnecessary initialization, but
> this seems like something we could screw up quite easily.
> 
> >  		r = -EFAULT;
> > -		if (copy_from_user(&kvm_userspace_mem, argp,
> > -						sizeof(kvm_userspace_mem)))
> > +		if (copy_from_user(&region_ext, argp,
> > +				sizeof(struct kvm_userspace_memory_region)))
> >  			goto out;
> > +		if (region_ext.region.flags & KVM_MEM_PRIVATE) {
> > +			int offset = offsetof(
> > +				struct kvm_userspace_memory_region_ext,
> > +				private_offset);
> > +			if (copy_from_user(&region_ext.private_offset,
> > +					   argp + offset,
> > +					   sizeof(region_ext) - offset))
> 
> In this patch, KVM_MEM_PRIVATE should result in an -EINVAL as it's not yet
> supported.  Copying the _ext on KVM_MEM_PRIVATE belongs in the "Expose KVM_MEM_PRIVATE"
> patch.

Agreed.

> 
> Mechnically, what about first reading flags via get_user(), and then doing a single
> copy_from_user()?  It's technically more work in the common case, and requires an
> extra check to guard against TOCTOU attacks, but this isn't a fast path by any means
> and IMO the end result makes it easier to understand the relationship between
> KVM_MEM_PRIVATE and the two different structs.

Will use this code, thanks for typing.

Chao
> 
> E.g.
> 
> 	case KVM_SET_USER_MEMORY_REGION: {
> 		struct kvm_user_mem_region region;
> 		unsigned long size;
> 		u32 flags;
> 
> 		memset(&region, 0, sizeof(region));
> 
> 		r = -EFAULT;
> 		if (get_user(flags, (u32 __user *)(argp + offsetof(typeof(region), flags))))
> 			goto out;
> 
> 		if (flags & KVM_MEM_PRIVATE)
> 			size = sizeof(struct kvm_userspace_memory_region_ext);
> 		else
> 			size = sizeof(struct kvm_userspace_memory_region);
> 		if (copy_from_user(&region, argp, size))
> 			goto out;
> 
> 		r = -EINVAL;
> 		if ((flags ^ region.flags) & KVM_MEM_PRIVATE)
> 			goto out;
> 
> 		r = kvm_vm_ioctl_set_memory_region(kvm, &region);
> 		break;
> 	}
> 
> > +				goto out;
> > +		}
> >  
> > -		r = kvm_vm_ioctl_set_memory_region(kvm, &kvm_userspace_mem);
> > +		r = kvm_vm_ioctl_set_memory_region(kvm, &region_ext);
> >  		break;
> >  	}
> >  	case KVM_GET_DIRTY_LOG: {
> > -- 
> > 2.17.1
> >
diff mbox series

Patch

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 8c06b8204fca..1d9dbef67715 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -11757,13 +11757,13 @@  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_region_ext m;
 
-		m.slot = id | (i << 16);
-		m.flags = 0;
-		m.guest_phys_addr = gpa;
-		m.userspace_addr = hva;
-		m.memory_size = size;
+		m.region.slot = id | (i << 16);
+		m.region.flags = 0;
+		m.region.guest_phys_addr = gpa;
+		m.region.userspace_addr = hva;
+		m.region.memory_size = size;
 		r = __kvm_set_memory_region(kvm, &m);
 		if (r < 0)
 			return ERR_PTR_USR(r);
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 3be8116079d4..c92c70174248 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -1082,9 +1082,9 @@  enum kvm_mr_change {
 };
 
 int kvm_set_memory_region(struct kvm *kvm,
-			  const struct kvm_userspace_memory_region *mem);
+		const struct kvm_userspace_memory_region_ext *region_ext);
 int __kvm_set_memory_region(struct kvm *kvm,
-			    const struct kvm_userspace_memory_region *mem);
+		const struct kvm_userspace_memory_region_ext *region_ext);
 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/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 69c318fdff61..d11a2628b548 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -1809,8 +1809,9 @@  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_region_ext *region_ext)
 {
+	const struct kvm_userspace_memory_region *mem = &region_ext->region;
 	struct kvm_memory_slot *old, *new;
 	struct kvm_memslots *slots;
 	enum kvm_mr_change change;
@@ -1913,24 +1914,24 @@  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_region_ext *region_ext)
 {
 	int r;
 
 	mutex_lock(&kvm->slots_lock);
-	r = __kvm_set_memory_region(kvm, mem);
+	r = __kvm_set_memory_region(kvm, region_ext);
 	mutex_unlock(&kvm->slots_lock);
 	return r;
 }
 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_region_ext *region_ext)
 {
-	if ((u16)mem->slot >= KVM_USER_MEM_SLOTS)
+	if ((u16)region_ext->region.slot >= KVM_USER_MEM_SLOTS)
 		return -EINVAL;
 
-	return kvm_set_memory_region(kvm, mem);
+	return kvm_set_memory_region(kvm, region_ext);
 }
 
 #ifndef CONFIG_KVM_GENERIC_DIRTYLOG_READ_PROTECT
@@ -4476,14 +4477,23 @@  static long kvm_vm_ioctl(struct file *filp,
 		break;
 	}
 	case KVM_SET_USER_MEMORY_REGION: {
-		struct kvm_userspace_memory_region kvm_userspace_mem;
+		struct kvm_userspace_memory_region_ext region_ext;
 
 		r = -EFAULT;
-		if (copy_from_user(&kvm_userspace_mem, argp,
-						sizeof(kvm_userspace_mem)))
+		if (copy_from_user(&region_ext, argp,
+				sizeof(struct kvm_userspace_memory_region)))
 			goto out;
+		if (region_ext.region.flags & KVM_MEM_PRIVATE) {
+			int offset = offsetof(
+				struct kvm_userspace_memory_region_ext,
+				private_offset);
+			if (copy_from_user(&region_ext.private_offset,
+					   argp + offset,
+					   sizeof(region_ext) - offset))
+				goto out;
+		}
 
-		r = kvm_vm_ioctl_set_memory_region(kvm, &kvm_userspace_mem);
+		r = kvm_vm_ioctl_set_memory_region(kvm, &region_ext);
 		break;
 	}
 	case KVM_GET_DIRTY_LOG: {