Re: [PATCH v3 02/15] KVM: x86: use u64_to_user_addr()

[Xu Yilun]

On Mon, Feb 26, 2024 at 02:03:31PM -0500, Paolo Bonzini wrote:
> There is no danger to the kernel if userspace provides a 64-bit value that
> has the high bits set, but for whatever reason happ[ens to resolve to an
                                                     ^

remove the messy char.

> address that has something mapped there.  KVM uses the checked version
> of put_user() in kvm_x86_dev_get_attr().

See from the code change, not just kvm_x86_dev_get_attr().

Thanks,
Yilun

> 
> Suggested-by: Sean Christopherson <seanjc@xxxxxxxxxx>
> Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> ---
>  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 f3f7405e0628..14c969782d73 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -4791,25 +4791,13 @@ 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))
> @@ -5664,12 +5652,9 @@ 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;
> @@ -5687,13 +5672,10 @@ 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;
> -- 
> 2.39.1
> 
> 
>