[RFCv2 08/16] KVM: Use GUP instead of copy_from/to_user() to access guest memory

[Kirill A. Shutemov]

New helpers copy_from_guest()/copy_to_guest() to be used if KVM memory
protection feature is enabled.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
---
 include/linux/kvm_host.h |  4 ++
 virt/kvm/kvm_main.c      | 90 +++++++++++++++++++++++++++++++---------
 2 files changed, 75 insertions(+), 19 deletions(-)

diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 05e3c2fb3ef7..380a64613880 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -504,6 +504,7 @@ struct kvm {
 	struct srcu_struct irq_srcu;
 	pid_t userspace_pid;
 	unsigned int max_halt_poll_ns;
+	bool mem_protected;
 };
 
 #define kvm_err(fmt, ...) \
@@ -728,6 +729,9 @@ void kvm_set_pfn_dirty(kvm_pfn_t pfn);
 void kvm_set_pfn_accessed(kvm_pfn_t pfn);
 void kvm_get_pfn(kvm_pfn_t pfn);
 
+int copy_from_guest(void *data, unsigned long hva, int len, bool protected);
+int copy_to_guest(unsigned long hva, const void *data, int len, bool protected);
+
 void kvm_release_pfn(kvm_pfn_t pfn, bool dirty, struct gfn_to_pfn_cache *cache);
 int kvm_read_guest_page(struct kvm *kvm, gfn_t gfn, void *data, int offset,
 			int len);
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index cf88233b819a..a9884cb8c867 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -2313,19 +2313,70 @@ static int next_segment(unsigned long len, int offset)
 		return len;
 }
 
+int copy_from_guest(void *data, unsigned long hva, int len, bool protected)
+{
+	int offset = offset_in_page(hva);
+	struct page *page;
+	int npages, seg;
+
+	if (!protected)
+		return __copy_from_user(data, (void __user *)hva, len);
+
+	might_fault();
+	kasan_check_write(data, len);
+	check_object_size(data, len, false);
+
+	while ((seg = next_segment(len, offset)) != 0) {
+		npages = get_user_pages_unlocked(hva, 1, &page, 0);
+		if (npages != 1)
+			return -EFAULT;
+		memcpy(data, page_address(page) + offset, seg);
+		put_page(page);
+		len -= seg;
+		hva += seg;
+		offset = 0;
+	}
+
+	return 0;
+}
+
+int copy_to_guest(unsigned long hva, const void *data, int len, bool protected)
+{
+	int offset = offset_in_page(hva);
+	struct page *page;
+	int npages, seg;
+
+	if (!protected)
+		return __copy_to_user((void __user *)hva, data, len);
+
+	might_fault();
+	kasan_check_read(data, len);
+	check_object_size(data, len, true);
+
+	while ((seg = next_segment(len, offset)) != 0) {
+		npages = get_user_pages_unlocked(hva, 1, &page, FOLL_WRITE);
+		if (npages != 1)
+			return -EFAULT;
+		memcpy(page_address(page) + offset, data, seg);
+		put_page(page);
+		len -= seg;
+		hva += seg;
+		offset = 0;
+	}
+
+	return 0;
+}
+
 static int __kvm_read_guest_page(struct kvm_memory_slot *slot, gfn_t gfn,
-				 void *data, int offset, int len)
+				 void *data, int offset, int len,
+				 bool protected)
 {
-	int r;
 	unsigned long addr;
 
 	addr = gfn_to_hva_memslot_prot(slot, gfn, NULL);
 	if (kvm_is_error_hva(addr))
 		return -EFAULT;
-	r = __copy_from_user(data, (void __user *)addr + offset, len);
-	if (r)
-		return -EFAULT;
-	return 0;
+	return copy_from_guest(data, addr + offset, len, protected);
 }
 
 int kvm_read_guest_page(struct kvm *kvm, gfn_t gfn, void *data, int offset,
@@ -2333,7 +2384,8 @@ int kvm_read_guest_page(struct kvm *kvm, gfn_t gfn, void *data, int offset,
 {
 	struct kvm_memory_slot *slot = gfn_to_memslot(kvm, gfn);
 
-	return __kvm_read_guest_page(slot, gfn, data, offset, len);
+	return __kvm_read_guest_page(slot, gfn, data, offset, len,
+				     kvm->mem_protected);
 }
 EXPORT_SYMBOL_GPL(kvm_read_guest_page);
 
@@ -2342,7 +2394,8 @@ int kvm_vcpu_read_guest_page(struct kvm_vcpu *vcpu, gfn_t gfn, void *data,
 {
 	struct kvm_memory_slot *slot = kvm_vcpu_gfn_to_memslot(vcpu, gfn);
 
-	return __kvm_read_guest_page(slot, gfn, data, offset, len);
+	return __kvm_read_guest_page(slot, gfn, data, offset, len,
+				     vcpu->kvm->mem_protected);
 }
 EXPORT_SYMBOL_GPL(kvm_vcpu_read_guest_page);
 
@@ -2415,7 +2468,8 @@ int kvm_vcpu_read_guest_atomic(struct kvm_vcpu *vcpu, gpa_t gpa,
 EXPORT_SYMBOL_GPL(kvm_vcpu_read_guest_atomic);
 
 static int __kvm_write_guest_page(struct kvm_memory_slot *memslot, gfn_t gfn,
-			          const void *data, int offset, int len)
+			          const void *data, int offset, int len,
+				  bool protected)
 {
 	int r;
 	unsigned long addr;
@@ -2423,7 +2477,8 @@ static int __kvm_write_guest_page(struct kvm_memory_slot *memslot, gfn_t gfn,
 	addr = gfn_to_hva_memslot(memslot, gfn);
 	if (kvm_is_error_hva(addr))
 		return -EFAULT;
-	r = __copy_to_user((void __user *)addr + offset, data, len);
+
+	r = copy_to_guest(addr + offset, data, len, protected);
 	if (r)
 		return -EFAULT;
 	mark_page_dirty_in_slot(memslot, gfn);
@@ -2435,7 +2490,8 @@ int kvm_write_guest_page(struct kvm *kvm, gfn_t gfn,
 {
 	struct kvm_memory_slot *slot = gfn_to_memslot(kvm, gfn);
 
-	return __kvm_write_guest_page(slot, gfn, data, offset, len);
+	return __kvm_write_guest_page(slot, gfn, data, offset, len,
+				      kvm->mem_protected);
 }
 EXPORT_SYMBOL_GPL(kvm_write_guest_page);
 
@@ -2444,7 +2500,8 @@ int kvm_vcpu_write_guest_page(struct kvm_vcpu *vcpu, gfn_t gfn,
 {
 	struct kvm_memory_slot *slot = kvm_vcpu_gfn_to_memslot(vcpu, gfn);
 
-	return __kvm_write_guest_page(slot, gfn, data, offset, len);
+	return __kvm_write_guest_page(slot, gfn, data, offset, len,
+				      vcpu->kvm->mem_protected);
 }
 EXPORT_SYMBOL_GPL(kvm_vcpu_write_guest_page);
 
@@ -2560,7 +2617,7 @@ int kvm_write_guest_offset_cached(struct kvm *kvm, struct gfn_to_hva_cache *ghc,
 	if (unlikely(!ghc->memslot))
 		return kvm_write_guest(kvm, gpa, data, len);
 
-	r = __copy_to_user((void __user *)ghc->hva + offset, data, len);
+	r = copy_to_guest(ghc->hva + offset, data, len, kvm->mem_protected);
 	if (r)
 		return -EFAULT;
 	mark_page_dirty_in_slot(ghc->memslot, gpa >> PAGE_SHIFT);
@@ -2581,7 +2638,6 @@ int kvm_read_guest_offset_cached(struct kvm *kvm, struct gfn_to_hva_cache *ghc,
 				 unsigned long len)
 {
 	struct kvm_memslots *slots = kvm_memslots(kvm);
-	int r;
 	gpa_t gpa = ghc->gpa + offset;
 
 	BUG_ON(len + offset > ghc->len);
@@ -2597,11 +2653,7 @@ int kvm_read_guest_offset_cached(struct kvm *kvm, struct gfn_to_hva_cache *ghc,
 	if (unlikely(!ghc->memslot))
 		return kvm_read_guest(kvm, gpa, data, len);
 
-	r = __copy_from_user(data, (void __user *)ghc->hva + offset, len);
-	if (r)
-		return -EFAULT;
-
-	return 0;
+	return copy_from_guest(data, ghc->hva + offset, len, kvm->mem_protected);
 }
 EXPORT_SYMBOL_GPL(kvm_read_guest_offset_cached);
 
-- 
2.26.2