Re: [PATCH] ppc/spapr: advertise secure boot in the guest device tree

[David Gibson <david@gibson.dropbear.id.au>]

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On Mon, May 10, 2021 at 10:07:13PM +1000, Daniel Axtens wrote:
> The ibm,secure-boot property of the / node determines how firmware
> and the operating system should enforce secure boot. The meaning
> of the various values are:
> 
>  0   - secure boot is disabled
>  1   - secure boot in log-only mode
>  2   - secure boot enabled and enforced
>  3-9 - secure boot enabled and enforced; requirements at the
>          discretion of the operating system
> 
> We expose this as two properties:
> 
>  - secure-boot: determines whether the property is advertised in the
>                 guest device tree. The default is false.
> 
>  - secure-boot-level: what value is advertised if enabled?
>                       The default is 2.
> 
> This doesn't make the firmware or OS actually _do_ any verification, it
> just advises them that they should.

So.. what's the point?  AFAIK we have no secure boot support in SLOF,
so what would advertising it in the device tree accomplish?

> 
> Signed-off-by: Daniel Axtens <dja@axtens.net>
> 
> ---
> 
> Linux already reads this property. Versions of SLOF and grub that do
> verification are available on my GitHub:
>  - github.com/daxtens/SLOF branch ibm,secure-boot (not production ready!)
>  - github.com/daxtens/grub branch appendedsig-2.06
> ---
>  hw/ppc/spapr.c         | 42 ++++++++++++++++++++++++++++++++++++++++++
>  include/hw/ppc/spapr.h |  4 ++++
>  2 files changed, 46 insertions(+)
> 
> diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
> index 3b1a5ed86518..544a412c3d18 100644
> --- a/hw/ppc/spapr.c
> +++ b/hw/ppc/spapr.c
> @@ -1157,6 +1157,20 @@ static void spapr_dt_hypervisor(SpaprMachineState *spapr, void *fdt)
>      }
>  }
>  
> +static void spapr_dt_stb(SpaprMachineState *spapr, void *fdt)
> +{
> +    /*
> +     * PowerVM may provide fw-secure-boot, which purports to tell a partition
> +     * if the underlying firmware was booted securely. It's not meaningful
> +     * for KVM as there are no agreed semantics for what it would mean (host
> +     * secure boot only gives you integrity for the host kernel, not host
> +     * qemu). So we omit the property for now.
> +     */
> +    if (spapr->secure_boot)
> +        _FDT(fdt_setprop_cell(fdt, 0, "ibm,secure-boot",
> +            spapr->secure_boot_level));
> +}
> +
>  void *spapr_build_fdt(SpaprMachineState *spapr, bool reset, size_t space)
>  {
>      MachineState *machine = MACHINE(spapr);
> @@ -1263,6 +1277,9 @@ void *spapr_build_fdt(SpaprMachineState *spapr, bool reset, size_t space)
>          spapr_dt_hypervisor(spapr, fdt);
>      }
>  
> +    /* /ibm,secureboot */
> +    spapr_dt_stb(spapr, fdt);
> +
>      /* Build memory reserve map */
>      if (reset) {
>          if (spapr->kernel_size) {
> @@ -3298,6 +3315,20 @@ static void spapr_set_host_serial(Object *obj, const char *value, Error **errp)
>      spapr->host_serial = g_strdup(value);
>  }
>  
> +static bool spapr_get_secure_boot(Object *obj, Error **errp)
> +{
> +    SpaprMachineState *spapr = SPAPR_MACHINE(obj);
> +
> +    return spapr->secure_boot;
> +}
> +
> +static void spapr_set_secure_boot(Object *obj, bool value, Error **errp)
> +{
> +    SpaprMachineState *spapr = SPAPR_MACHINE(obj);
> +
> +    spapr->secure_boot = value;
> +}
> +
>  static void spapr_instance_init(Object *obj)
>  {
>      SpaprMachineState *spapr = SPAPR_MACHINE(obj);
> @@ -3353,6 +3384,17 @@ static void spapr_instance_init(Object *obj)
>          spapr_get_host_serial, spapr_set_host_serial);
>      object_property_set_description(obj, "host-serial",
>          "Host serial number to advertise in guest device tree");
> +
> +    /* If we have secure boot, the default level is 2: enable and enforce */
> +    spapr->secure_boot_level = 2;
> +    object_property_add_bool(obj, "secure-boot",
> +        spapr_get_secure_boot, spapr_set_secure_boot);
> +    object_property_set_description(obj, "secure-boot",
> +        "Advertise secure boot in the guest device tree");
> +    object_property_add_uint8_ptr(obj, "secure-boot-level",
> +        &spapr->secure_boot_level, OBJ_PROP_FLAG_READWRITE);
> +    object_property_set_description(obj, "secure-boot-level",
> +        "Level of secure boot advertised in the guest device tree");
>  }
>  
>  static void spapr_machine_finalizefn(Object *obj)
> diff --git a/include/hw/ppc/spapr.h b/include/hw/ppc/spapr.h
> index c421410e3fb8..d829d0c27011 100644
> --- a/include/hw/ppc/spapr.h
> +++ b/include/hw/ppc/spapr.h
> @@ -210,6 +210,10 @@ struct SpaprMachineState {
>      int fwnmi_machine_check_interlock;
>      QemuCond fwnmi_machine_check_interlock_cond;
>  
> +    /* Secure Boot */
> +    bool secure_boot;
> +    uint8_t secure_boot_level;
> +
>      /*< public >*/
>      char *kvm_type;
>      char *host_model;

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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