From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 6969CC433F5 for ; Wed, 15 Dec 2021 13:44:36 +0000 (UTC) Received: from localhost ([::1]:33804 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1mxUaB-0001yl-8a for qemu-devel@archiver.kernel.org; Wed, 15 Dec 2021 08:44:35 -0500 Received: from eggs.gnu.org ([209.51.188.92]:59580) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1mxU8Z-0001LQ-34 for qemu-devel@nongnu.org; Wed, 15 Dec 2021 08:16:03 -0500 Received: from [2607:f8b0:4864:20::b30] (port=38679 helo=mail-yb1-xb30.google.com) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.90_1) (envelope-from ) id 1mxU8X-00050f-4f for qemu-devel@nongnu.org; Wed, 15 Dec 2021 08:16:02 -0500 Received: by mail-yb1-xb30.google.com with SMTP id v64so55055448ybi.5 for ; Wed, 15 Dec 2021 05:16:00 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linaro.org; s=google; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc:content-transfer-encoding; bh=gM6mFIK2UrpQvcXb+mChAgCxKybKifKP5Azjm0zqeB8=; b=Pq5hksYVPGwo7Vw5mZTtqHXgjJQm803IxmjEt7WERURL5/keaPAIrKPDDuTYlXScK8 zmWNSRl13eRdDivHBsUrPWJqw5Y9mPKIrssyGOselCWHMNIzPiaDBS/ZMaaqDymTggDC 93X+QKQGumF2jWpfMySdAoJrcET/fp6MVIDbOG6NySsvSSLcvniMswp8kOhcAQNaLks3 sm4njv3A04dlkigPcJJzTOMDI0A7SZDD4pr7SifN5e1H5e098L3ElZlt11rtqA0cEuhu eee/uIXGCcnx85WAZBarQkcQR0v7ah7sfswhEYWXVzPa1DYB7Ug5mSj8YDRIlx3cWA0B R7/g== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc:content-transfer-encoding; bh=gM6mFIK2UrpQvcXb+mChAgCxKybKifKP5Azjm0zqeB8=; b=YonQZcs1Xc/O2dzH+Y19y8HMeYMzv1PMkRutcpXA2hSsJqKt1Kn6F3lDM+zr+NHvKz bsjz2KTQCpCxQnxWR7DrDTVxn3VEYFpSESohNOv8Vs6uwxmHMMr2FfPL8i+NZ9n46Bls ZL2w03SOfMVmkCg/l5JPOsEy3MAsgo3Q4K5nM3YdVmC6hKpSQygoiglwoyD1qjrehMyq 43QZRxJsEOX/hOIc5U30KMPOcbPpCe6D32NU1iJLFLQ/IG48eh09Gs8fNvSJvV91je1a 8t5Tz/8jmv2AvGBCw1wwc/79ShVkMKZj1UiIAm/ic1EafIquTgs6GhqOdRfqx2Ve/HFS vsWA== X-Gm-Message-State: AOAM530SHpGUn7QDcQIWApU1ZcYIDXQrP2hPWHDFhwxhYtRFGEc6cpIR JCDSCB/02KRU/CEJQIUfN5kTpyU8/wxYi9n2ysPLkQ== X-Google-Smtp-Source: ABdhPJywNhvA3FVevV5ejsIO69dXayAfsk7pk3SadZxSgGfnWJ/JWLP/ORavyrGcZVHvRDNhjMcmZqmnHBq4HczOCzE= X-Received: by 2002:a25:e792:: with SMTP id e140mr6189596ybh.426.1639574158977; Wed, 15 Dec 2021 05:15:58 -0800 (PST) MIME-Version: 1.0 References: <20211215120926.1696302-1-alex.bennee@linaro.org> In-Reply-To: <20211215120926.1696302-1-alex.bennee@linaro.org> From: Ilias Apalodimas Date: Wed, 15 Dec 2021 15:15:22 +0200 Message-ID: Subject: Re: [PATCH] hw/arm: add control knob to disable kaslr_seed via DTB To: =?UTF-8?B?QWxleCBCZW5uw6ll?= Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Host-Lookup-Failed: Reverse DNS lookup failed for 2607:f8b0:4864:20::b30 (failed) Received-SPF: pass client-ip=2607:f8b0:4864:20::b30; envelope-from=ilias.apalodimas@linaro.org; helo=mail-yb1-xb30.google.com X-Spam_score_int: -12 X-Spam_score: -1.3 X-Spam_bar: - X-Spam_report: (-1.3 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RDNS_NONE=0.793, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, WEIRD_QUOTING=0.001 autolearn=no 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: Peter Maydell , qemu-arm@nongnu.org, Jerome Forissier , qemu-devel@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Hi Alex, On Wed, 15 Dec 2021 at 14:09, Alex Benn=C3=A9e wro= te: > > 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 Benn=C3=A9e > Cc: Ilias Apalodimas > Cc: Jerome Forissier > --- > 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 30da05dfe0..4496612e89 100644 > --- a/hw/arm/virt.c > +++ b/hw/arm/virt.c > @@ -248,11 +248,15 @@ static void create_fdt(VirtMachineState *vms) > > /* /chosen must exist for load_dtb to fill in necessary properties l= ater */ > 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 > @@ -2236,6 +2240,20 @@ static void virt_set_its(Object *obj, bool value, = Error **errp) > vms->its =3D value; > } > > +static bool virt_get_kaslr_dtb_seed(Object *obj, Error **errp) > +{ > + VirtMachineState *vms =3D VIRT_MACHINE(obj); > + > + return vms->kaslr_dtb_seed; > +} > + > +static void virt_set_kaslr_dtb_seed(Object *obj, bool value, Error **err= p) > +{ > + VirtMachineState *vms =3D VIRT_MACHINE(obj); > + > + vms->kaslr_dtb_seed =3D value; > +} > + > static char *virt_get_oem_id(Object *obj, Error **errp) > { > VirtMachineState *vms =3D VIRT_MACHINE(obj); > @@ -2765,6 +2783,13 @@ static void virt_machine_class_init(ObjectClass *o= c, 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); > @@ -2829,6 +2854,9 @@ static void virt_instance_init(Object *obj) > /* MTE is disabled by default. */ > vms->mte =3D false; > > + /* Supply a kaslr-seed by default */ > + vms->kaslr_dtb_seed =3D true; > + > vms->irqmap =3D a15irqmap; > > virt_flash_create(vms); > -- > 2.30.2 > This is particularly useful if the bootloader uses a TPM to measures the DTB and end up with a measured boot flow. Acked-by: Ilias Apalodimas