KVM: SVM: no need to call access_ok() in LAUNCH_MEASURE command

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 <viro@ZenIV.linux.org.uk>
Fixes: 0d0736f76347 (KVM: SVM: Add support for KVM_SEV_LAUNCH_MEASURE ...)
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Radim Krčmář <rkrcmar@redhat.com>
Cc: Borislav Petkov <bp@suse.de>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Cc: linux-kernel@vger.kernel.org
Cc: Joerg Roedel <joro@8bytes.org>
Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index b3e488a748281aa5f3d319861ae2ab4bfca3e65c..ca69d53d7e6dbc3352d5ce31371fe72dc84310ab 100644 (file)
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -6236,16 +6236,18 @@ e_free:
 
 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 @@ cmd:
                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);