linux-kernel - Re: [PATCH] KVM: SVM: Invert user pointer casting in SEV {en,de}crypt helpers

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Date:   Fri, 7 May 2021 09:40:54 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Brijesh Singh <brijesh.singh@....com>,
        Tom Lendacky <thomas.lendacky@....com>,
        Ashish Kalra <ashish.kalra@....com>
Subject: Re: [PATCH] KVM: SVM: Invert user pointer casting in SEV {en,de}crypt
 helpers

On 07/05/21 01:15, Sean Christopherson wrote:
> Invert the user pointer params for SEV's helpers for encrypting and
> decrypting guest memory so that they take a pointer and cast to an
> unsigned long as necessary, as opposed to doing the opposite.  Tagging a
> non-pointer as __user is confusing and weird since a cast of some form
> needs to occur to actually access the user data.  This also fixes Sparse
> warnings triggered by directly consuming the unsigned longs, which are
> "noderef" due to the __user tag.
> 
> Cc: Brijesh Singh <brijesh.singh@....com>
> Cc: Tom Lendacky <thomas.lendacky@....com>
> Cc: Ashish Kalra <ashish.kalra@....com>
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> ---
>   arch/x86/kvm/svm/sev.c | 24 +++++++++++-------------
>   1 file changed, 11 insertions(+), 13 deletions(-)
> 
> diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
> index a9d8d6aafdb8..bba4544fbaba 100644
> --- a/arch/x86/kvm/svm/sev.c
> +++ b/arch/x86/kvm/svm/sev.c
> @@ -763,7 +763,7 @@ static int __sev_dbg_decrypt(struct kvm *kvm, unsigned long src_paddr,
>   }
>   
>   static int __sev_dbg_decrypt_user(struct kvm *kvm, unsigned long paddr,
> -				  unsigned long __user dst_uaddr,
> +				  void __user *dst_uaddr,
>   				  unsigned long dst_paddr,
>   				  int size, int *err)
>   {
> @@ -787,8 +787,7 @@ static int __sev_dbg_decrypt_user(struct kvm *kvm, unsigned long paddr,
>   
>   	if (tpage) {
>   		offset = paddr & 15;
> -		if (copy_to_user((void __user *)(uintptr_t)dst_uaddr,
> -				 page_address(tpage) + offset, size))
> +		if (copy_to_user(dst_uaddr, page_address(tpage) + offset, size))
>   			ret = -EFAULT;
>   	}
>   
> @@ -800,9 +799,9 @@ static int __sev_dbg_decrypt_user(struct kvm *kvm, unsigned long paddr,
>   }
>   
>   static int __sev_dbg_encrypt_user(struct kvm *kvm, unsigned long paddr,
> -				  unsigned long __user vaddr,
> +				  void __user *vaddr,
>   				  unsigned long dst_paddr,
> -				  unsigned long __user dst_vaddr,
> +				  void __user *dst_vaddr,
>   				  int size, int *error)
>   {
>   	struct page *src_tpage = NULL;
> @@ -810,13 +809,12 @@ static int __sev_dbg_encrypt_user(struct kvm *kvm, unsigned long paddr,
>   	int ret, len = size;
>   
>   	/* If source buffer is not aligned then use an intermediate buffer */
> -	if (!IS_ALIGNED(vaddr, 16)) {
> +	if (!IS_ALIGNED((unsigned long)vaddr, 16)) {
>   		src_tpage = alloc_page(GFP_KERNEL);
>   		if (!src_tpage)
>   			return -ENOMEM;
>   
> -		if (copy_from_user(page_address(src_tpage),
> -				(void __user *)(uintptr_t)vaddr, size)) {
> +		if (copy_from_user(page_address(src_tpage), vaddr, size)) {
>   			__free_page(src_tpage);
>   			return -EFAULT;
>   		}
> @@ -830,7 +828,7 @@ static int __sev_dbg_encrypt_user(struct kvm *kvm, unsigned long paddr,
>   	 *   - copy the source buffer in an intermediate buffer
>   	 *   - use the intermediate buffer as source buffer
>   	 */
> -	if (!IS_ALIGNED(dst_vaddr, 16) || !IS_ALIGNED(size, 16)) {
> +	if (!IS_ALIGNED((unsigned long)dst_vaddr, 16) || !IS_ALIGNED(size, 16)) {
>   		int dst_offset;
>   
>   		dst_tpage = alloc_page(GFP_KERNEL);
> @@ -855,7 +853,7 @@ static int __sev_dbg_encrypt_user(struct kvm *kvm, unsigned long paddr,
>   			       page_address(src_tpage), size);
>   		else {
>   			if (copy_from_user(page_address(dst_tpage) + dst_offset,
> -					   (void __user *)(uintptr_t)vaddr, size)) {
> +					   vaddr, size)) {
>   				ret = -EFAULT;
>   				goto e_free;
>   			}
> @@ -935,15 +933,15 @@ static int sev_dbg_crypt(struct kvm *kvm, struct kvm_sev_cmd *argp, bool dec)
>   		if (dec)
>   			ret = __sev_dbg_decrypt_user(kvm,
>   						     __sme_page_pa(src_p[0]) + s_off,
> -						     dst_vaddr,
> +						     (void __user *)dst_vaddr,
>   						     __sme_page_pa(dst_p[0]) + d_off,
>   						     len, &argp->error);
>   		else
>   			ret = __sev_dbg_encrypt_user(kvm,
>   						     __sme_page_pa(src_p[0]) + s_off,
> -						     vaddr,
> +						     (void __user *)vaddr,
>   						     __sme_page_pa(dst_p[0]) + d_off,
> -						     dst_vaddr,
> +						     (void __user *)dst_vaddr,
>   						     len, &argp->error);
>   
>   		sev_unpin_memory(kvm, src_p, n);
> 

Queued, thnaks.

Paolo