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[213.175.37.12]) by smtp.gmail.com with ESMTPSA id d5sm19208611wrs.61.2022.01.05.06.49.14 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 05 Jan 2022 06:49:14 -0800 (PST) Date: Wed, 5 Jan 2022 15:49:13 +0100 From: Andrew Jones To: Alex =?utf-8?Q?Benn=C3=A9e?= Subject: Re: [PATCH v1 21/34] hw/arm: add control knob to disable kaslr_seed via DTB Message-ID: <20220105144913.2nitpxzmdyucgr7g@gator> References: <20220105135009.1584676-1-alex.bennee@linaro.org> <20220105135009.1584676-22-alex.bennee@linaro.org> MIME-Version: 1.0 In-Reply-To: <20220105135009.1584676-22-alex.bennee@linaro.org> Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=drjones@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=170.10.129.124; envelope-from=drjones@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -31 X-Spam_score: -3.2 X-Spam_bar: --- X-Spam_report: (-3.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.372, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, WEIRD_QUOTING=0.001 autolearn=unavailable autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: fam@euphon.net, Peter Maydell , berrange@redhat.com, Heinrich Schuchardt , Ilias Apalodimas , qemu-devel@nongnu.org, f4bug@amsat.org, pbonzini@redhat.com, aurelien@aurel32.net, stefanha@redhat.com, crosa@redhat.com, Jerome Forissier , "open list:Virt" Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Wed, Jan 05, 2022 at 01:49:56PM +0000, Alex Bennée wrote: > Generally a guest needs an external source of randomness to properly > enable things like address space randomisation. However in a trusted > boot environment where the firmware will cryptographically verify > components having random data in the DTB will cause verification to > fail. Add a control knob so we can prevent this being added to the > system DTB. > > Signed-off-by: Alex Bennée > Tested-by: Heinrich Schuchardt > Acked-by: Ilias Apalodimas > Acked-by: Jerome Forissier > Message-Id: <20211215120926.1696302-1-alex.bennee@linaro.org> > --- > docs/system/arm/virt.rst | 7 +++++++ > include/hw/arm/virt.h | 1 + > hw/arm/virt.c | 32 ++++++++++++++++++++++++++++++-- > 3 files changed, 38 insertions(+), 2 deletions(-) > > diff --git a/docs/system/arm/virt.rst b/docs/system/arm/virt.rst > index 850787495b..c86a4808df 100644 > --- a/docs/system/arm/virt.rst > +++ b/docs/system/arm/virt.rst > @@ -121,6 +121,13 @@ ras > Set ``on``/``off`` to enable/disable reporting host memory errors to a guest > using ACPI and guest external abort exceptions. The default is off. > > +kaslr-dtb-seed > + Set ``on``/``off`` to pass a random seed via the guest dtb to use for features > + like address space randomisation. The default is ``on``. You will want > + to disable it if your trusted boot chain will verify the DTB it is > + passed. It would be the responsibility of the firmware to come up > + with a seed and pass it on if it wants to. > + > Linux guest kernel configuration > """""""""""""""""""""""""""""""" > > diff --git a/include/hw/arm/virt.h b/include/hw/arm/virt.h > index dc6b66ffc8..acd0665fe7 100644 > --- a/include/hw/arm/virt.h > +++ b/include/hw/arm/virt.h > @@ -148,6 +148,7 @@ struct VirtMachineState { > bool virt; > bool ras; > bool mte; > + bool kaslr_dtb_seed; > OnOffAuto acpi; > VirtGICType gic_version; > VirtIOMMUType iommu; > diff --git a/hw/arm/virt.c b/hw/arm/virt.c > index 6bce595aba..1781e47c76 100644 > --- a/hw/arm/virt.c > +++ b/hw/arm/virt.c > @@ -247,11 +247,15 @@ static void create_fdt(VirtMachineState *vms) > > /* /chosen must exist for load_dtb to fill in necessary properties later */ > qemu_fdt_add_subnode(fdt, "/chosen"); > - create_kaslr_seed(ms, "/chosen"); > + if (vms->kaslr_dtb_seed) { > + create_kaslr_seed(ms, "/chosen"); > + } > > if (vms->secure) { > qemu_fdt_add_subnode(fdt, "/secure-chosen"); > - create_kaslr_seed(ms, "/secure-chosen"); > + if (vms->kaslr_dtb_seed) { > + create_kaslr_seed(ms, "/secure-chosen"); > + } > } > > /* Clock node, for the benefit of the UART. The kernel device tree > @@ -2235,6 +2239,20 @@ static void virt_set_its(Object *obj, bool value, Error **errp) > vms->its = value; > } > > +static bool virt_get_kaslr_dtb_seed(Object *obj, Error **errp) > +{ > + VirtMachineState *vms = VIRT_MACHINE(obj); > + > + return vms->kaslr_dtb_seed; > +} > + > +static void virt_set_kaslr_dtb_seed(Object *obj, bool value, Error **errp) > +{ > + VirtMachineState *vms = VIRT_MACHINE(obj); > + > + vms->kaslr_dtb_seed = value; > +} > + > static char *virt_get_oem_id(Object *obj, Error **errp) > { > VirtMachineState *vms = VIRT_MACHINE(obj); > @@ -2764,6 +2782,13 @@ static void virt_machine_class_init(ObjectClass *oc, void *data) > "Set on/off to enable/disable " > "ITS instantiation"); > > + object_class_property_add_bool(oc, "kaslr-dtb-seed", > + virt_get_kaslr_dtb_seed, > + virt_set_kaslr_dtb_seed); > + object_class_property_set_description(oc, "kaslr-dtb-seed", > + "Set off to disable passing of kaslr " > + "dtb node to guest"); > + > object_class_property_add_str(oc, "x-oem-id", > virt_get_oem_id, > virt_set_oem_id); > @@ -2828,6 +2853,9 @@ static void virt_instance_init(Object *obj) > /* MTE is disabled by default. */ > vms->mte = false; > > + /* Supply a kaslr-seed by default */ > + vms->kaslr_dtb_seed = true; > + > vms->irqmap = a15irqmap; > > virt_flash_create(vms); > -- > 2.30.2 > > Reviewed-by: Andrew Jones