Re: [PATCH 2/3] KVM: x86: add system attribute to retrieve full set of supported xsave states

[Yang Zhong]

On Thu, Jan 27, 2022 at 03:35:50PM +0000, Sean Christopherson wrote:
> On Wed, Jan 26, 2022, Paolo Bonzini wrote:
> > +static int kvm_x86_dev_get_attr(struct kvm_device_attr *attr)
> > +{
> > +	if (attr->group)
> > +		return -ENXIO;
> > +
> > +	switch (attr->attr) {
> > +	case KVM_X86_XCOMP_GUEST_SUPP:
> > +		if (put_user(supported_xcr0, (u64 __user *)attr->addr))
> 
> Deja vu[*].
> 
>   arch/x86/kvm/x86.c: In function ‘kvm_x86_dev_get_attr’:
>   arch/x86/kvm/x86.c:4345:46: error: cast to pointer from integer of different size [-Werror=int-to-pointer-cast]
>    4345 |                 if (put_user(supported_xcr0, (u64 __user *)attr->addr))
>         |                                              ^
>   arch/x86/include/asm/uaccess.h:221:31: note: in definition of macro ‘do_put_user_call’
>     221 |         register __typeof__(*(ptr)) __val_pu asm("%"_ASM_AX);           \
>         |                               ^~~
>   arch/x86/kvm/x86.c:4345:21: note: in expansion of macro ‘put_user’
>    4345 |                 if (put_user(supported_xcr0, (u64 __user *)attr->addr))
>         |                     ^~~~~~~~
>   arch/x86/kvm/x86.c:4345:46: error: cast to pointer from integer of different size [-Werror=int-to-pointer-cast]
>    4345 |                 if (put_user(supported_xcr0, (u64 __user *)attr->addr))
>         |                                              ^
>   arch/x86/include/asm/uaccess.h:223:21: note: in definition of macro ‘do_put_user_call’
>     223 |         __ptr_pu = (ptr);                                               \
>         |                     ^~~
>   arch/x86/kvm/x86.c:4345:21: note: in expansion of macro ‘put_user’
>    4345 |                 if (put_user(supported_xcr0, (u64 __user *)attr->addr))
>         |                     ^~~~~~~~
>   arch/x86/kvm/x86.c:4345:46: error: cast to pointer from integer of different size [-Werror=int-to-pointer-cast]
>    4345 |                 if (put_user(supported_xcr0, (u64 __user *)attr->addr))
>         |                                              ^
>   arch/x86/include/asm/uaccess.h:230:45: note: in definition of macro ‘do_put_user_call’
>     230 |                        [size] "i" (sizeof(*(ptr)))                      \
>         |                                             ^~~
>   arch/x86/kvm/x86.c:4345:21: note: in expansion of macro ‘put_user’
>    4345 |                 if (put_user(supported_xcr0, (u64 __user *)attr->addr))
> 
> Given that we're collectively 2 for 2 in mishandling {g,s}et_attr(), what about
> a prep pacth like so?  Compile tested only...
>

  Sean, It's strange that I could not find those issues in my last day's build.
  
  My build environment:
  #make -v
  GNU Make 4.3
  
  # gcc -v
  gcc version 9.3.0 (Ubuntu 9.3.0-17ubuntu1~20.04)

  I will apply your extra patch to check again, thanks!
  

  Yang

 
> From: Sean Christopherson <seanjc@xxxxxxxxxx>
> Date: Thu, 27 Jan 2022 07:31:53 -0800
> Subject: [PATCH] KVM: x86: Add a helper to retrieve userspace address from
>  kvm_device_attr
> 
> Add a helper to handle converting the u64 userspace address embedded in
> struct kvm_device_attr into a userspace pointer, it's all too easy to
> forget the intermediate "unsigned long" cast as well as the truncation
> check.
> 
> No functional change intended.
> 
> Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
> ---
>  arch/x86/kvm/x86.c | 28 +++++++++++++++++++++-------
>  1 file changed, 21 insertions(+), 7 deletions(-)
> 
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 8033eca6f3a1..67836f7c71f5 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -4335,14 +4335,28 @@ 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(-EFAULT);
> +	return uaddr;
> +}
> +
>  static int kvm_x86_dev_get_attr(struct kvm_device_attr *attr)
>  {
> +	u64 __user *uaddr = kvm_get_attr_addr(attr);
> +
>  	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(supported_xcr0, (u64 __user *)attr->addr))
> +		if (put_user(supported_xcr0, uaddr))
>  			return -EFAULT;
>  		return 0;
>  	default:
> @@ -5070,11 +5084,11 @@ 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 = (u64 __user *)(unsigned long)attr->addr;
> +	u64 __user *uaddr = kvm_get_attr_addr(attr);
>  	int r;
> 
> -	if ((u64)(unsigned long)uaddr != attr->addr)
> -		return -EFAULT;
> +	if (IS_ERR(uaddr))
> +		return PTR_ERR(uaddr);
> 
>  	switch (attr->attr) {
>  	case KVM_VCPU_TSC_OFFSET:
> @@ -5093,12 +5107,12 @@ 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 = (u64 __user *)(unsigned long)attr->addr;
> +	u64 __user *uaddr = kvm_get_attr_addr(attr);
>  	struct kvm *kvm = vcpu->kvm;
>  	int r;
> 
> -	if ((u64)(unsigned long)uaddr != attr->addr)
> -		return -EFAULT;
> +	if (IS_ERR(uaddr))
> +		return PTR_ERR(uaddr);
> 
>  	switch (attr->attr) {
>  	case KVM_VCPU_TSC_OFFSET: {
> --
> 
> 
> 
> [*] https://lore.kernel.org/all/20211007231647.3553604-1-seanjc@xxxxxxxxxx
> 
> 
> > +			return -EFAULT;
> > +		return 0;
> > +	default:
> > +		return -ENXIO;
> > +		break;
> > +	}
> > +}
> > +