author: Nicholas Piggin <npiggin@gmail.com> 2021-07-20 20:43:09 +1000
committer: Greg Kroah-Hartman <gregkh@linuxfoundation.org> 2021-07-28 14:37:36 +0200
commit: 35e114e6f84ab559eb35a5ac73590d23a43f22ba
parent: 3d98808e2414bdb06a7e392260ea17fa7929a5ee
Commit Summary:
Diffstat:
1 file changed, 22 insertions, 3 deletions
diff --git a/arch/powerpc/kvm/book3s_rtas.c b/arch/powerpc/kvm/book3s_rtas.c
index c5e677508d3b..0f847f1e5ddd 100644
--- a/arch/powerpc/kvm/book3s_rtas.c
+++ b/arch/powerpc/kvm/book3s_rtas.c
@@ -242,6 +242,17 @@ int kvmppc_rtas_hcall(struct kvm_vcpu *vcpu)
* value so we can restore it on the way out.
*/
orig_rets = args.rets;
+ if (be32_to_cpu(args.nargs) >= ARRAY_SIZE(args.args)) {
+ /*
+ * Don't overflow our args array: ensure there is room for
+ * at least rets[0] (even if the call specifies 0 nret).
+ *
+ * Each handler must then check for the correct nargs and nret
+ * values, but they may always return failure in rets[0].
+ */
+ rc = -EINVAL;
+ goto fail;
+ }
args.rets = &args.args[be32_to_cpu(args.nargs)];
mutex_lock(&vcpu->kvm->arch.rtas_token_lock);
@@ -269,9 +280,17 @@ int kvmppc_rtas_hcall(struct kvm_vcpu *vcpu)
fail:
/*
* We only get here if the guest has called RTAS with a bogus
- * args pointer. That means we can't get to the args, and so we
- * can't fail the RTAS call. So fail right out to userspace,
- * which should kill the guest.
+ * args pointer or nargs/nret values that would overflow the
+ * array. That means we can't get to the args, and so we can't
+ * fail the RTAS call. So fail right out to userspace, which
+ * should kill the guest.
+ *
+ * SLOF should actually pass the hcall return value from the
+ * rtas handler call in r3, so enter_rtas could be modified to
+ * return a failure indication in r3 and we could return such
+ * errors to the guest rather than failing to host userspace.
+ * However old guests that don't test for failure could then
+ * continue silently after errors, so for now we won't do this.
*/
return rc;
}