On 23/02/2018 19:36, Brijesh Singh wrote:
> Using the access_ok() to validate the input before issuing the SEV
> command does not buy us anything in this case. If userland is
> giving us a garbage pointer then copy_to_user() will catch it when we try
> to return the measurement.
> 
> Suggested-by: Al Viro <v...@zeniv.linux.org.uk>
> Fixes: 0d0736f76347 (KVM: SVM: Add support for KVM_SEV_LAUNCH_MEASURE ...)
> Cc: Paolo Bonzini <pbonz...@redhat.com>
> Cc: "Radim Krčmář" <rkrc...@redhat.com>
> Cc: Borislav Petkov <b...@suse.de>
> Cc: Tom Lendacky <thomas.lenda...@amd.com>
> Cc: linux-kernel@vger.kernel.org
> Cc: Joerg Roedel <j...@8bytes.org>
> Signed-off-by: Brijesh Singh <brijesh.si...@amd.com>
> ---
> 
> We no longer need patch [1]. This patch implements Al Viro's recommendation 
> [2]
> 
> [1] https://marc.info/?l=linux-kernel&m=151905677729098&w=2.
> [2] https://marc.info/?l=linux-kernel&m=151923536116467&w=2
> 
>  arch/x86/kvm/svm.c | 16 +++++++---------
>  1 file changed, 7 insertions(+), 9 deletions(-)
> 
> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
> index b3e488a74828..ca69d53d7e6d 100644
> --- a/arch/x86/kvm/svm.c
> +++ b/arch/x86/kvm/svm.c
> @@ -6236,16 +6236,18 @@ static int sev_launch_update_data(struct kvm *kvm, 
> struct kvm_sev_cmd *argp)
>  
>  static int sev_launch_measure(struct kvm *kvm, struct kvm_sev_cmd *argp)
>  {
> +     void __user *measure = (void __user *)(uintptr_t)argp->data;
>       struct kvm_sev_info *sev = &kvm->arch.sev_info;
>       struct sev_data_launch_measure *data;
>       struct kvm_sev_launch_measure params;
> +     void __user *p = NULL;
>       void *blob = NULL;
>       int ret;
>  
>       if (!sev_guest(kvm))
>               return -ENOTTY;
>  
> -     if (copy_from_user(&params, (void __user *)(uintptr_t)argp->data, 
> sizeof(params)))
> +     if (copy_from_user(&params, measure, sizeof(params)))
>               return -EFAULT;
>  
>       data = kzalloc(sizeof(*data), GFP_KERNEL);
> @@ -6256,17 +6258,13 @@ static int sev_launch_measure(struct kvm *kvm, struct 
> kvm_sev_cmd *argp)
>       if (!params.len)
>               goto cmd;
>  
> -     if (params.uaddr) {
> +     p = (void __user *)(uintptr_t)params.uaddr;
> +     if (p) {
>               if (params.len > SEV_FW_BLOB_MAX_SIZE) {
>                       ret = -EINVAL;
>                       goto e_free;
>               }
>  
> -             if (!access_ok(VERIFY_WRITE, params.uaddr, params.len)) {
> -                     ret = -EFAULT;
> -                     goto e_free;
> -             }
> -
>               ret = -ENOMEM;
>               blob = kmalloc(params.len, GFP_KERNEL);
>               if (!blob)
> @@ -6290,13 +6288,13 @@ static int sev_launch_measure(struct kvm *kvm, struct 
> kvm_sev_cmd *argp)
>               goto e_free_blob;
>  
>       if (blob) {
> -             if (copy_to_user((void __user *)(uintptr_t)params.uaddr, blob, 
> params.len))
> +             if (copy_to_user(p, blob, params.len))
>                       ret = -EFAULT;
>       }
>  
>  done:
>       params.len = data->len;
> -     if (copy_to_user((void __user *)(uintptr_t)argp->data, &params, 
> sizeof(params)))
> +     if (copy_to_user(measure, &params, sizeof(params)))
>               ret = -EFAULT;
>  e_free_blob:
>       kfree(blob);
> 

Queued, thanks Brijesh and Al.

Paolo

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