Re: [patch RFC] kvm, cpuid: silence a buffer overflow warning

[Paolo Bonzini <pbonzini@redhat.com>]

Il 20/02/2014 13:34, Dan Carpenter ha scritto:
> This seems like a harmless off by one overflow if "i" is the last
> element in the vcpu->arch.cpuid_entries[] array.
> 
> Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
> ---
> Not tested.  I always wonder if it's worth fixing these or if it's worth
> reporting them?  Either of those seem like a lot of work for something
> harmless.

Could it oops if cpuid_nent is INT_MAX?  If so, it's not entirely harmless.
In this case I'd rather take the occasion to cleanup the code like this
(compile-tested):

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index 9fed5bedaad6..2fd6e7169936 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -656,18 +656,19 @@ out:
 static int move_to_next_stateful_cpuid_entry(struct kvm_vcpu *vcpu, int i)
 {
 	struct kvm_cpuid_entry2 *e = &vcpu->arch.cpuid_entries[i];
-	int j, nent = vcpu->arch.cpuid_nent;
+	struct kvm_cpuid_entry2 *ej;
+	int j = i, nent = vcpu->arch.cpuid_nent;
 
 	e->flags &= ~KVM_CPUID_FLAG_STATE_READ_NEXT;
+
 	/* when no next entry is found, the current entry[i] is reselected */
-	for (j = i + 1; ; j = (j + 1) % nent) {
-		struct kvm_cpuid_entry2 *ej = &vcpu->arch.cpuid_entries[j];
-		if (ej->function = e->function) {
-			ej->flags |= KVM_CPUID_FLAG_STATE_READ_NEXT;
-			return j;
-		}
-	}
-	return 0; /* silence gcc, even though control never reaches here */
+	do {
+		j = (j + 1) % nent;
+		ej = &vcpu->arch.cpuid_entries[j];
+	} while (ej->function != e->function);
+
+	ej->flags |= KVM_CPUID_FLAG_STATE_READ_NEXT;
+	return j;
 }
 
 /* find an entry with matching function, matching index (if needed), and that

What do you think?

Paolo