KVM: x86: Hoist input checks in kvm_add_msr_filter()

In ioctl KVM_X86_SET_MSR_FILTER, input from user space is validated
after a memdup_user(). For invalid inputs we'd memdup and then call
kfree unnecessarily. Hoist input validation to avoid kfree altogether.

Signed-off-by: Siddharth Chandrasekaran <sidcha@amazon.de>
Message-Id: <20210503122111.13775-1-sidcha@amazon.de>
Reviewed-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index cebdaa1..102f116 100644 (file)
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -5468,14 +5468,18 @@ static void kvm_free_msr_filter(struct kvm_x86_msr_filter *msr_filter)
 static int kvm_add_msr_filter(struct kvm_x86_msr_filter *msr_filter,
                              struct kvm_msr_filter_range *user_range)
 {
-       struct msr_bitmap_range range;
        unsigned long *bitmap = NULL;
        size_t bitmap_size;
-       int r;
 
        if (!user_range->nmsrs)
                return 0;
 
+       if (user_range->flags & ~(KVM_MSR_FILTER_READ | KVM_MSR_FILTER_WRITE))
+               return -EINVAL;
+
+       if (!user_range->flags)
+               return -EINVAL;
+
        bitmap_size = BITS_TO_LONGS(user_range->nmsrs) * sizeof(long);
        if (!bitmap_size || bitmap_size > KVM_MSR_FILTER_MAX_BITMAP_SIZE)
                return -EINVAL;
@@ -5484,31 +5488,15 @@ static int kvm_add_msr_filter(struct kvm_x86_msr_filter *msr_filter,
        if (IS_ERR(bitmap))
                return PTR_ERR(bitmap);
 
-       range = (struct msr_bitmap_range) {
+       msr_filter->ranges[msr_filter->count] = (struct msr_bitmap_range) {
                .flags = user_range->flags,
                .base = user_range->base,
                .nmsrs = user_range->nmsrs,
                .bitmap = bitmap,
        };
 
-       if (range.flags & ~(KVM_MSR_FILTER_READ | KVM_MSR_FILTER_WRITE)) {
-               r = -EINVAL;
-               goto err;
-       }
-
-       if (!range.flags) {
-               r = -EINVAL;
-               goto err;
-       }
-
-       /* Everything ok, add this range identifier. */
-       msr_filter->ranges[msr_filter->count] = range;
        msr_filter->count++;
-
        return 0;
-err:
-       kfree(bitmap);
-       return r;
 }
 
 static int kvm_vm_ioctl_set_msr_filter(struct kvm *kvm, void __user *argp)