linux-kernel - [PATCH v4 03/15] KVM: x86: use u64_to_user

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Message-ID: <20240318233352.2728327-4-pbonzini@redhat.com>
Date: Mon, 18 Mar 2024 19:33:40 -0400
From: Paolo Bonzini <pbonzini@...hat.com>
To: linux-kernel@...r.kernel.org,
	kvm@...r.kernel.org
Cc: michael.roth@....com,
	isaku.yamahata@...el.com,
	seanjc@...gle.com
Subject: [PATCH v4 03/15] KVM: x86: use u64_to_user_addr()

There is no danger to the kernel if 32-bit userspace provides a 64-bit
value that has the high bits set, but for whatever reason happens to
resolve to an address that has something mapped there.  KVM uses the
checked version of get_user() and put_user(), so any faults are caught
properly.

Suggested-by: Sean Christopherson <seanjc@...gle.com>
Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
---
 arch/x86/kvm/x86.c | 24 +++---------------------
 1 file changed, 3 insertions(+), 21 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 47d9f03b7778..3d2029402513 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -4842,25 +4842,13 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
 	return r;
 }
 
-static inline void __user *kvm_get_attr_addr(struct kvm_device_attr *attr)
-{
-	void __user *uaddr = (void __user*)(unsigned long)attr->addr;
-
-	if ((u64)(unsigned long)uaddr != attr->addr)
-		return ERR_PTR_USR(-EFAULT);
-	return uaddr;
-}
-
 static int kvm_x86_dev_get_attr(struct kvm_device_attr *attr)
 {
-	u64 __user *uaddr = kvm_get_attr_addr(attr);
+	u64 __user *uaddr = u64_to_user_ptr(attr->addr);
 
 	if (attr->group)
 		return -ENXIO;
 
-	if (IS_ERR(uaddr))
-		return PTR_ERR(uaddr);
-
 	switch (attr->attr) {
 	case KVM_X86_XCOMP_GUEST_SUPP:
 		if (put_user(kvm_caps.supported_xcr0, uaddr))
@@ -5712,12 +5700,9 @@ static int kvm_arch_tsc_has_attr(struct kvm_vcpu *vcpu,
 static int kvm_arch_tsc_get_attr(struct kvm_vcpu *vcpu,
 				 struct kvm_device_attr *attr)
 {
-	u64 __user *uaddr = kvm_get_attr_addr(attr);
+	u64 __user *uaddr = u64_to_user_ptr(attr->addr);
 	int r;
 
-	if (IS_ERR(uaddr))
-		return PTR_ERR(uaddr);
-
 	switch (attr->attr) {
 	case KVM_VCPU_TSC_OFFSET:
 		r = -EFAULT;
@@ -5735,13 +5720,10 @@ static int kvm_arch_tsc_get_attr(struct kvm_vcpu *vcpu,
 static int kvm_arch_tsc_set_attr(struct kvm_vcpu *vcpu,
 				 struct kvm_device_attr *attr)
 {
-	u64 __user *uaddr = kvm_get_attr_addr(attr);
+	u64 __user *uaddr = u64_to_user_ptr(attr->addr);
 	struct kvm *kvm = vcpu->kvm;
 	int r;
 
-	if (IS_ERR(uaddr))
-		return PTR_ERR(uaddr);
-
 	switch (attr->attr) {
 	case KVM_VCPU_TSC_OFFSET: {
 		u64 offset, tsc, ns;
-- 
2.43.0