On Mon, Sep 14, 2020 at 04:05:22PM +0800, Chester Lin wrote:
> Hi Ard,
>
> On Fri, Sep 11, 2020 at 06:01:09PM +0300, Ard Biesheuvel wrote:
> > On Fri, 4 Sep 2020 at 10:29, Chester Lin <clin@xxxxxxxx> wrote:
> > >
> > > Add a new UEFI parameter: "linux,uefi-secure-boot" in fdt boot params
> > > as other architectures have done in their own boot data. For example,
> > > the boot_params->secure_boot in x86.
> > >
> > > Signed-off-by: Chester Lin <clin@xxxxxxxx>
> >
> > Why do we need this flag? Can't the OS simply check the variable directly?
> >
>
> In fact, there's a difficulty to achieve this.
>
> When linux kernel is booting on ARM, the runtime services are enabled later on.
> It's done by arm_enable_runtime_services(), which is registered as an early_initcall.
> Before it calls efi_native_runtime_setup(), all EFI runtime callbacks are still
> NULL so calling efi.get_variable() will cause NULL pointer dereference.
>
> There's a case that arch_ima_get_secureboot() can be called in early boot stage.
> For example, when you try to set "ima_appraise=off" in kernel command line, it's
> actually handled early:
>
> [ 0.000000] Kernel command line: BOOT_IMAGE=/boot/Image-5.9.0-rc3-9.gdd61cda-
> vanilla root=UUID=a88bfb80-8abb-425c-a0f3-ad317465c28b splash=silent mitigations
> =auto ignore_loglevel earlycon=pl011,mmio,0x9000000 console=ttyAMA0 ima_appraise=off
> [ 0.000000] ima: Secure boot enabled: ignoring ima_appraise=off boot parameter option
> [ 0.000000] Dentry cache hash table entries: 1048576 (order: 11, 8388608 bytes, linear)
>
> However EFI services are remapped and enabled afterwards.
>
> [ 0.082286] rcu: Hierarchical SRCU implementation.
> [ 0.089592] Remapping and enabling EFI services.
> [ 0.097509] smp: Bringing up secondary CPUs ...
>
> Another problem is that efi_rts_wq is created in subsys_initcall so we have to
> wait for both EFI services mapping and the workqueue get initiated before calling
> efi.get_variable() on ARM.
>
> The only way I can think of is to put a flag via fdt params. May I have your
> suggestions? I will appreciate if there's any better approach.
>
> Thanks,
> Chester
Ping. May I have some suggestions here?
Thanks,
Chester
>
> > > ---
> > > drivers/firmware/efi/libstub/fdt.c | 39 +++++++++++++++++++++++++++++-
> > > 1 file changed, 38 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/firmware/efi/libstub/fdt.c b/drivers/firmware/efi/libstub/fdt.c
> > > index 11ecf3c4640e..c9a341e4715f 100644
> > > --- a/drivers/firmware/efi/libstub/fdt.c
> > > +++ b/drivers/firmware/efi/libstub/fdt.c
> > > @@ -136,6 +136,10 @@ static efi_status_t update_fdt(void *orig_fdt, unsigned long orig_fdt_size,
> > > if (status)
> > > goto fdt_set_fail;
> > >
> > > + status = fdt_setprop_var(fdt, node, "linux,uefi-secure-boot", fdt_val32);
> > > + if (status)
> > > + goto fdt_set_fail;
> > > +
> > > if (IS_ENABLED(CONFIG_RANDOMIZE_BASE)) {
> > > efi_status_t efi_status;
> > >
> > > @@ -199,6 +203,24 @@ static efi_status_t update_fdt_memmap(void *fdt, struct efi_boot_memmap *map)
> > > return EFI_SUCCESS;
> > > }
> > >
> > > +static efi_status_t update_fdt_secboot(void *fdt, u32 secboot)
> > > +{
> > > + int node = fdt_path_offset(fdt, "/chosen");
> > > + u32 fdt_val32;
> > > + int err;
> > > +
> > > + if (node < 0)
> > > + return EFI_LOAD_ERROR;
> > > +
> > > + fdt_val32 = cpu_to_fdt32(secboot);
> > > +
> > > + err = fdt_setprop_inplace_var(fdt, node, "linux,uefi-secure-boot", fdt_val32);
> > > + if (err)
> > > + return EFI_LOAD_ERROR;
> > > +
> > > + return EFI_SUCCESS;
> > > +}
> > > +
> > > struct exit_boot_struct {
> > > efi_memory_desc_t *runtime_map;
> > > int *runtime_entry_count;
> > > @@ -208,6 +230,9 @@ struct exit_boot_struct {
> > > static efi_status_t exit_boot_func(struct efi_boot_memmap *map,
> > > void *priv)
> > > {
> > > + efi_status_t status;
> > > + enum efi_secureboot_mode secboot_status;
> > > + u32 secboot_var = 0;
> > > struct exit_boot_struct *p = priv;
> > > /*
> > > * Update the memory map with virtual addresses. The function will also
> > > @@ -217,7 +242,19 @@ static efi_status_t exit_boot_func(struct efi_boot_memmap *map,
> > > efi_get_virtmap(*map->map, *map->map_size, *map->desc_size,
> > > p->runtime_map, p->runtime_entry_count);
> > >
> > > - return update_fdt_memmap(p->new_fdt_addr, map);
> > > + status = update_fdt_memmap(p->new_fdt_addr, map);
> > > +
> > > + if (status != EFI_SUCCESS)
> > > + return status;
> > > +
> > > + secboot_status = efi_get_secureboot();
> > > +
> > > + if (secboot_status == efi_secureboot_mode_enabled)
> > > + secboot_var = 1;
> > > +
> > > + status = update_fdt_secboot(p->new_fdt_addr, secboot_var);
> > > +
> > > + return status;
> > > }
> > >
> > > #ifndef MAX_FDT_SIZE
> > > --
> > > 2.26.1
> > >
> >
