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:

quoted

On Fri, 4 Sep 2020 at 10:29, Chester Lin [off-list ref] wrote:

quoted

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 <redacted>

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

quoted

quoted

---
 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