From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:35811) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ffhlC-000625-Ng for qemu-devel@nongnu.org; Wed, 18 Jul 2018 04:24:35 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ffhl8-0005yV-Pj for qemu-devel@nongnu.org; Wed, 18 Jul 2018 04:24:34 -0400 From: David Hildenbrand Date: Wed, 18 Jul 2018 10:24:25 +0200 Message-Id: <20180718082425.14834-1-david@redhat.com> Subject: [Qemu-devel] [PATCH] s390x/cpumodel: fix segmentation fault when baselining models List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-s390x@nongnu.org Cc: qemu-devel@nongnu.org, Richard Henderson , Alexander Graf , Cornelia Huck , Christian Borntraeger , Thomas Huth , Chris Venteicher , Collin Walling , David Hildenbrand Usually, when baselining two CPU models, whereby one of them has base CPU features disabled (e.g. z14-base,msa=off), we fallback to an older model that did not have these features in the base model. We always try to create a "sane" CPU model (as far as possible), and one part of it is that removing base features is no good and to be avoided. Now, if we disable base features that were part of a z900, we're out of luck. We won't find a CPU model and QEMU will segfault. This is a scenario that should never happen in real life, but it can be used to crash QEMU. So let's make something like this: { "execute": "query-cpu-model-baseline", "arguments" : { "modela": { "name": "z14-base", "props": {"esan3" : false}}, "modelb": { "name": "z14"}} } Produce: {"return": {"model": {"name": "z900-base", "props": {"esan3": false}}}} Instead of segfaulting. This could of course be improved (e.g. to z14-base,esan3=false), however as this ususally won't happen, let's just avoid crashes. Signed-off-by: David Hildenbrand --- target/s390x/cpu_models.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/target/s390x/cpu_models.c b/target/s390x/cpu_models.c index cfdbccf46d..13a5d4f095 100644 --- a/target/s390x/cpu_models.c +++ b/target/s390x/cpu_models.c @@ -716,6 +716,12 @@ CpuModelBaselineInfo *arch_query_cpu_model_baseline(CpuModelInfo *infoa, model.def = s390_find_cpu_def(cpu_type, max_gen, max_gen_ga, model.features); + + /* models without early base features (esan3) are bad - fallback to z900 */ + if (!model.def) { + model.def = s390_find_cpu_def(0x2064, 7, 1, NULL); + } + /* strip off features not part of the max model */ bitmap_and(model.features, model.features, model.def->full_feat, S390_FEAT_MAX); -- 2.17.1